Aesthetics

Aesthetic phenomena can be explained by universal biases in animal brains and sensory systems, rather than improbable coevolutionary connections to differential survival.

© 2025 Andrew Hodgson

Some kind of aesthetic activity is apparently a feature of all the 3,000 or so distinguishable cultures that are to be found on the earth’s surface. This suggests strongly that art grows out of some fundamental characteristics of the human nervous system.

—D. E. Berlyne, Aesthetics and Psychobiology (1971)

Aesthetics receives strangely little attention in scientific and philosophical circles, given the evidence of a sense of beauty in thousands of species and the ubiquity of aesthetic phenomena in biology and human culture. Examples include music and song, dance, flowers and fruits, poetry and lyrics, stories, characters, plays, paintings, decoration of all kinds, games and sports, toys, clothing, architecture, gods, myths, heroes, rituals, temples, films, bodies and gestures, cosmetics, clothing, hairstyles, celebrations and holidays, gardens and parks, parties, festivals, products, logos, names, bright solids like gold, silver, diamonds, jewelry, ivory, teeth, pearls and coins, soft body parts like breasts, lips and tongues, surprising things such as jokes, gambling, plot twists and presents, and figurative language including idioms, metaphors, oxymorons, hyperbole, irony, paradox, proverbs, understatements, euphemisms and alliteration.

Not every aesthetic thing is accounted for, of course, and attractive natural features of the world like streams, waterfalls, beaches, sunsets, eclipses, starry night skies, mountains, falling snow and rainbows aren’t included, although they’re aesthetic, and of special interest because they show it’s not unusual for animals to be amused by phenomena that weren’t created or didn’t evolve to amuse us. Our sense of beauty is broad enough to incorporate stimuli we have no reason to be concerned with, a subtle suggestion that its origin is disconnected from whatever purposes we imagine it to serve, and that preferences in general predate the evolution of beautiful things.

The existence of beauty itself doesn’t need an explanation. It exists because we select for it while ignoring or rejecting what we judge to be relatively unexceptional or displeasing. The mystery is why we find some experiences more desirable, or at least more tolerable, than others, why we so often agree about what they are, with each other and other animals, and what it is about the structure of aesthetic things that makes us like them. Aesthetics is primarily concerned with the source and persistence of psychological biases such as those for music over noise, dance over normal movement, flowers over leaves, colorful patterns over colorless invariance and generally with the existence of a common set of biases for attractive things, rather than the things themselves.

Even though the primary functions of the brain must be survival and reproduction, it’s also responsible for a wide variety of phenomena that can’t be understand as functional in these ways. Brains have to mix the physical characteristics of solids and fluids in order to maintain their structure, capture and transport energy, transport particles, support electrical impulses and perform any other essential physiological function. At the same time, somehow, it embodies animal preferences. It might not even be possible to put together a brain that functions well physiologically without introducing some amount of non-functional noise, or psychological by-products, such as aesthetic preferences for auditory and visual mixtures of regularity and variation. Certain types of preferences (and behaviors) are probably selected for indirectly through the apparent physical prerequisite that solidness and fluidity must be combined in the construction of a brain. Preferences and behaviors that don’t contribute in any obvious way to survival, or which greatly exceed in their magnitude that which would serve any apparent fitness-related purpose, might be explained as such by-products.

Darwin didn’t suggest that ornaments, songs and dances evolve because they indicate obscure, beneficial hereditary advantages, or that they come about through random, incomprehensible genetic feedback loops. He said they evolve in response to widespread preferences for similar stimuli in many different kinds of animals, through an aesthetic system of bias and effect (1871):

On the other hand, I willingly admit that a great number of male animals, as all our most gorgeous birds, some fishes, reptiles, and mammals, and a host of magnificently coloured butterflies, have been rendered beautiful for beauty’s sake. But this has been effected through sexual selection, that is, by the more beautiful males having been continually preferred by the females, and not for the delight of man. So it is with the music of birds. We may infer from all this that a nearly similar taste for beautiful colours and for musical sounds runs through a large part of the animal kingdom.

In Darwin’s view, something about the “common constitution” of the nervous system must be responsible for the evolution of beauty in animals (1888):

How the sense of beauty in its simplest form — that is, the reception of a peculiar kind of pleasure from certain colours, forms and sounds — was first developed in the mind of man and of the lower animals, is a very obscure subject. The same sort of difficulty is presented if we enquire how it is that certain flavours and odours give pleasure, and others displeasure. Habit in all these cases appears to have come to a certain extent into play; but there must be some fundamental cause in the constitution of the nervous system in each species.

What’s needed in order to account for similar preferences in so many species, from the “lower” animals to “man,” is something that’s the same about the brains of insects, fishes, reptiles, birds and mammals, ruling out factors like brain size, body size, intelligence, encephalization quotient, ecology or recent evolutionary history, leaving few potential common factors to consider, one of them being the physical complexity of plasma membranes in neurons, that which makes a brain thoroughly soft by comparison to other body parts and nonliving matter. Like beauty, complexity of this kind in the brain hasn’t received much attention, perhaps because it’s assumed to be an unimportant side effect of other properties. Instead, it appears to be essential to sensation, consciousness and preferences, so that a brain works more like a highly sensitive thermometer than a computer, with more exciting perceptual qualities corresponding to a greater increase in brain temperature than less exciting qualities.

In ancient Greece the word “aesthetic” meant the experience of a perception or feeling. Now, of course, it means beautiful or the study of beauty. The transition, connecting the senses with attractiveness, is comparable to the contemporary situation of “sensation” and “sensational,” or the word “like,” meaning both “similar to” and “attracted to,” or the meanings of “taste,” and the concept that art imitates life and vice versa. Empedocles’ claim that we see “fondness by fondness,” almost 2,500 years ago, also fits the idea that there’s a correspondence between beauty and the structure of the mind. If the correspondence is real, in some way, it would be as though we already knew it, collectively, and inadvertently constructed language to reflect the fact.

The present, thermoaesthetic perspective is a departure from mainstream views in that the unconscious biases responsible for beauty are assumed to have come into existence during the process of sensory system evolution, always in advance of their effects, as opposed to arising repeatedly in unlikely coevolutionary interactions between the sexes with unrealistic connections to survival. For instance, an appreciation for patterns of brightness mixed with darkness arose with sensitivity to light and dark and remained in place throughout the evolution of animals. That for contrasting colors and rainbows arose with color sensitivity and persisted despite the diversity that makes animal species different otherwise. Those for complex alternating patterns of sound with silence and dynamism with stasis go back to the ability to hear and detect motion, and so on.

Notes

Or shall we seek our answer, rather, in some psychological theory, like many of the most distinguished nineteenth-century ethnologists—Bastian, for instance, Tylor, and Frazer—attributing such cross-cultural accords to “the effect,” as Frazer put it, “of similar causes acting alike on the similar constitution of the human mind in different countries and under different skies”? Do such images, that is to say, take form naturally in the psyche? Can they be assumed and even expected to appear spontaneously, in dreams, in visions, in mythological figurations, any place on earth, wherever man has made his home?

— Campbell, The Flight of the Wild Gander (1987)

Universality

On the whole, birds appear to be the most aesthetic of all animals, excepting of course man, and they have nearly the same taste for the beautiful as we have.

— Charles Darwin (see Prum 2017)

To say tastes are unique, that they can’t be accounted for, or that beauty is “only in the eye of the beholder,” is a way of saying beauty and taste are random and dismissing the massive overlap of agreement about what’s likable and what isn’t. An extreme version of this view depicts a scenario in which one person has no idea what any other person will like or dislike, so that every time somebody happens to come up with and create something others find beautiful it’s a fortunate accident.

In reality, on the contrary, we know almost exactly what kinds of things we can say or do in any situation to be charming, repulsive, or something in between, and this wouldn’t be possible without a shared set of inclinations, or “common sense.” Similarly, artists can make art using their own sense of beauty because of how closely it tends to correspond with that of their audience. To some extent, our feelings about stimuli must be the same due to common elements of sensory systems, as Edmund Burke (2005) pointed out in A Philosophical Inquiry Into the Origin of Our Ideas of the Sublime and Beautiful, 1757:

We do and we must suppose, that as the conformation of their organs are nearly or altogether the same in all men, so the manner of perceiving external objects is in all men the same, or with little difference. We are satisfied that what appears to be light to one eye, appears light to another; that what seems sweet to one palate, is sweet to another; that what is dark and bitter to this man, is likewise dark and bitter to that; and we conclude in the same manner of great and little, hard and soft, hot and cold, rough and smooth; and indeed of all the natural qualities and affections of bodies. If we suffer ourselves to imagine, that their senses present to different men different images of things, this sceptical proceeding will make every sort of reasoning on every subject vain and frivolous, even that sceptical reasoning itself which had persuaded us to entertain a doubt concerning the agreement of our perceptions. But as there will be little doubt that bodies present similar images to the whole species, it must necessarily be allowed, that the pleasures and the pains which every object excites in one man, it must raise in all mankind, whilst it operates naturally, simply, and by its proper powers only: for if we deny this, we must imagine that the same cause, operating in the same manner, and on subjects of the same kind, will produce different effects; which would be highly absurd.

In the current context a single bias is taken to be responsible for all the independent instances of a given aesthetic effect, regardless of whether it was created culturally or evolved by mate choice. This has the advantage of agreeing with conventional thinking and the terminology already in place due to our collective understanding of aesthetic things. For instance, we think of birds as singing real songs and dancing real dances, conventionally calling their behavior by the same name as our own versions of the same conduct. The differences are not enough, apparently, to cause us to think of them in different terms.

To some extent, we know we’re hearing a song because sound, loudness, high notes and surprising variation are punctuated over short periods by silence, quietness, lower-pitched notes and predictable repetition. Relative simplicity regarding these qualities tends to characterize less amusing, less intricate, nonmusical communication. All of what we refer to as dancing in birds, fish, spiders and others, which can be as simple as expressing a little extra motion or asymmetry in the central, lower or posterior areas of the body, is understood as dancing just as real as our own, and in all cases there must be something about the brain that allows an animal to distinguish it from other types of motion.

Flowers must differ visually from leaves in some essential way that allows them to be recognized as such and admired by people and pollinators, and the brains of all species that admire flowers must have features that facilitate the admiration. The areas of the brain responsible for flower evolution are biased to select for complexity to the extent that the flowering part of a plant is complicated, visually, relative to its leaves and stems. The name “flower” itself, alluding to flow, is a clue to how we recognize them and how they seduce us.

The rule of discernibility applies to all conventionally aesthetic things. Jokes are somehow distinct from serious statements. Poetry sounds different than prose. Playing feels different from working. Myths and fantastical stories differ from everyday life. In each case, some process occurring in the part of the brain responsible for judging its appeal tells us whether we like it or not, and it’s predictable that the process is somehow the same every time from the fact that we put the things we like together in a group, calling them all “aesthetic,” for instance. There must be specific, determinable features that differentiate what we like from comparable but less interesting experiences.

Sensory Bias

What an odd thing it is to see an entire species — billions of people — playing with, listening to, meaningless tonal patterns, occupied and preoccupied for much of their time by what they call ‘music.’

— Oliver Sacks, Musicophilia (2008)

For beneath the first depth, namely that of the earliest civilizations — which are but the foreground of the long backward reach of the prehistory of our race — there rest the centuries, millenniums, indeed the centuries of millenniums of primitive man, the mighty hunter, the more primitive root-and-bug collector, back for more than half a million years. And there is a third depth, even deeper, and darker, below that, below the ultimate horizon of humanity. For we shall find the ritual dance among the birds, the fish, the apes and the bees.

— Joseph Campbell, The Masks of God: Primitive Mythology (2020)

Currently popular scientific approaches to beauty don’t address its structure, and they ignore the problem of its persistence and consistency across widely unrelated species. The most prevalent perspective regarding music, dance and elaborate shapes and coloration maintains that they evolve to demonstrate a good body or good genes, somehow more reliably than other attributes, indirectly benefiting a mate with a coevolving preference for the trait by allowing them to capture and pass on the genetic goodness to their own offspring. Such approaches don’t explain the complexity of sexually selected traits, or why, of all the things animals could do to prove themselves, and the vast number of more direct vitality-determining biases that could evolve, countless numbers of varied species have relentlessly converged on the particular scenario of preferring a complicated song, dance, shape or pattern.

We shouldn’t think of this convergence as somehow inevitable, that songs for instance represent such a large subset of the possible vocalizations an animal can make that the event of evolving to sing is hard to avoid statistically, any more than we think it’s inevitable a large proportion of human cultures would resort to singing instead of talking as a means of relaying relevant information simply because we’ve run out of more direct alternatives. The same argument applies to other aesthetic phenomena. They come about entirely because we select for them over less desirable stimuli, not because they’re inevitable or likely as members of a limited set of possibilities.

The second most popular scientific explanation for beauty and preferences, also a coevolutionary approach that doesn’t address the consistency, complexity or persistence of aesthetic traits is Fisherian runaway sexual selection (Fisher 1930, O’Donald 1967, Lande 1981, Kirkpatrick 1982), in which preference/trait pairs result from mathematically conceivable genetic feedback loops for no particular reason, or “beauty happens,” as Prum puts it in The Evolution of Beauty (2018), which otherwise argues against good genes as a realistic mechanism. Fisher’s model assumes an initial period in which a trait favored slightly by natural selection also randomly happens to be favored by certain mates, causing genes for the trait and those for the preference to increasingly occur together in succeeding generations. The preference and trait reinforce each other in a positive feedback loop, and the process continues until sexual selection for the trait and natural selection against it are in balance. The sequence of steps involved and the number of times they would need to play out independently but somehow lead to similar results across species makes this an extremely unlikely scheme compared to good genes, and especially compared to the idea that preferences simply exist by default.

The sensory bias model of sexual selection is a recently developed (West-Eberhard 1979, 1984; Ryan 1990, Ryan and Keddy-Hector 1992, Basolo 1996), relatively simple and intuitive alternative to good genes and Fisherian runaway. It predicts that side effects arise in the process of sensory system and brain evolution, causing preferences that generate selection for matching traits despite potentially reducing survival, arguably circling back, after more than 100 years of science, to Darwin’s original thinking (1896):

When male animals utter sounds in order to please the females, they would naturally employ those which are sweet to the ears of the species; and it appears that the same sounds are often pleasing to widely different animals, owing to the similarity of their nervous systems, as we ourselves perceive in the singing of birds and even in the chirping of certain tree-frogs giving us pleasure.

Sensory bias can be distinguished from other models in that the preference for a trait evolves prior to and in a different context than the trait preferred, non-coevolutionarily. Such biases could be originally adaptive, evolving through direct selection, by improving prey detection ability for instance, or they could be “hidden,” in that they’re an incidental by-product with no original, subsequent or current fitness-related function (see Ryan 1990, Enquist and Arak 1993, Endler and Basolo 1998, Arnqvist 2006).

Sensory bias appears to have played a role in the evolution of “courtship trembling” behavior in Neumania papillator water mites (Proctor 1991, 1992), complex mating calls in the Tungara frog Physalaemus pustulosus (Ryan and Rand 1990), complex swords in swordtail fishes (Basolo 1990, 1995, 1996), long, flowing tails in widowbirds (Pryke and Andersson 2002), orange spots in the guppy Poecilia reticulata (Rodd et al. 2002), song structure in Costa’s hummingbird Calypte costae (Clark and Feo 2009), song repertoires in birds (Collins 1999), nuptial food gifts in insects (Sakaluk 2000), egg-spots in Cichlids (Egger et al. 2011), mud pillar (Christy 1995) and sand hood (Christy 2003) building in the fiddler crabs Uca beebei and Uca musica, red pelage and skin colors in primates (Fernandez and Morris 2007), pollinator attraction in orchids (Schiestl and Cozzolino 2008), Anoline lizard head bobbing patterns (Fleishman 1992) and mate color preferences in birds (Møller and Erritzøe 2010). Preferences for entirely novel signals, like red leg bands in zebra finches Taeniopygia guttata (Burley et al. 1982), white crests in finches (Burley and Symanski 1998) and gene transfer-induced red color in zebrafish (Owen et al. 2012) indicate that preferences can exist independently of favored traits.

That organisms so widely separated taxonomically, ecologically and neurologically as humans, in every culture, whales (Payne and McVay 1971), bats (Behr and Helversen 2004), mice (Holy and Guo 2005), frogs (Searcy and Andersson 1986), about 5,000 species of birds (Hartshorne 1973), numerous different types of insects and other animals have an apparent preference for complex, song-like auditory stimuli strongly suggests the involvement of common elements in sensory systems, and it’s difficult to imagine so many different populations and species being subject to a common ecological factor that could possibly drive direct, adaptive selection leading all of them to a desire for song.

There’s no reason to believe other animals have strange, unidentifiable but somehow functional reasons for performing and enjoying songs and dances, particularly when we know that for us the reason is only the pleasure we take in experiencing the patterns that make them up. The problem with assuming independent origins of preferences for song in many different singing animals might be illustrated by the absurdity of the idea that unique preferences for the behavior had to evolve separately in every human culture rather than being in place to begin with, especially given the lack of a function for human song (Darwin 1871):

As neither the enjoyment nor the capacity of producing musical notes are faculties of the least use to man in reference to his daily habits of life, they must be ranked amongst the most mysterious with which he is endowed.

The 300 distinct notes and 66 types of songs of the winter wren Troglodytes troglodytes (Kroodsma 1980), or the 58 elements, 15 separate behaviors and 10 plumate ornaments distinguished by Scholes (2006) in the dance of Carola’s parotia (Parotia carolae) represent behaviors that are undeniably more complicated than what would suffice for the purpose of conveying a signal of condition. Unless we assume the songs of wrens came into existence fully formed, without increasing in complexity over time, these birds have been amused by every shorter, simpler evolutionary version of the song in addition to the current one. Parotias must have been impressed by every historical parotia dance, and by every new element as it was added, at the same time consistently rejecting potential mates who didn’t perform movements approaching the extremely complicated sequence currently in use. The existence of such traits is much easier to understand with a general preference for complexity in place prior to and throughout their evolution.

Humans have no adaptive business being so affectionate about flowers, given that we don’t get food from or pollinate any of them naturally. One common theoretical approach in such cases is to trace the origin of a currently inexplicable trait, an attraction to flowers in this case, back to a common ancestor with a species that does have a reason to express it. For humans, an attraction to flowers would seem to go back at least beyond our most recent common ancestor with the many species of nectar-feeding, flower-pollinating birds, or prior to the split between mammals and reptiles, around 300 million years, probably before the first flowers existed. Notably, human interaction with flowers isn’t restricted to those produced by plants. We paint abstract versions of them on objects and canvases, carve or mold them into architecture, stitch them into clothing and tattoo them on our bodies, an indication that animals enjoy the shape in general, not only in the practical, ecological context of foraging.

To explain why insects and birds share a preference for flowers one would predict it was present in the brains of the ancestors of both groups, going back over 500 million years, to a time long before flowers, which, according to Sauquet et al. (2017), appeared somewhere between 140 and 250 million years ago. Preferences for song and dance, judging by their effects, in the courtship of both insects and birds, for instance, probably go back to the same early times, persisting with no regard for the taxonomic distance between species, across massive discrepancies in body size, brain size and ecology, suggesting that every animal has some capacity to understand and admire them by default, as a consequence of universal, inevitable aspects of sensory system structure.

The proposition that every singing species of bird evolved an inclination for musical sounds independently is hardly different from proposing that every species of bird separately evolved the ability to fly, except that in the first case there’s no practical reason for them to do so, and therefore even less reason to believe it happened more than once. There are obvious benefits to flying. It seems very likely that doing so has allowed birds to be, according to Darwin, the second most aesthetic type of animal, and it’s very unlikely to be a coincidence that birds and humans also have in common such an unusual degree of freedom from ecological limitations related to resource availability, predation and unsuitable environmental conditions. This isn’t to say animals don’t evolve the tendency to be attracted to a specific flowering plant, or to enjoy the particular type of singing or dancing of their own species more than others; it’s that they do so in the context of preexisting, ever-present biases for these types of stimuli.

Even if we did historically pollinate a particular flower, for some hardly imaginable, naturally selected purpose, this would only explain our attraction to that kind of flower, not most or all of them. This problem applies in general because so many particular flowers are pollinated by multiple animal species, which themselves pollinate multiple kinds of flowers. Assuming animals like flowers to begin with helps explain the success angiosperms have had in using floral shapes to exploit us. If humans had a history, evolutionarily, of performing a song or dance in a courtship display to compete for mates, traditional thinking would only explain the enticement of whatever particular song we were singing or dance we were doing, not the massive variety of those we’ve created, and no obvious advantage would accrue to a population expanding the use of song or dance outside the context of sex into that of religion, patriotism, ceremony, celebration and general entertainment.

Musical patterns apparently flow through the animal brain from the auditory cortex to the motor areas, translating outwardly into alternating body shapes and actions with the same, semi-predictable, simultaneously regular and random (disorder~order) structure as the music, as though the substance of the brain is offering little resistance. That humans relate dance to music and integrate the two phenomena in practice shows we have an automatic, unconscious way of recognizing some degree of aesthetic overlap or equivalence between them, probably because they have similar effects on the brain.

There’s a growing list of animals that dance to human music, meaning the equivalence is likely recognized universally. Cotton-top tamarin monkeys respond emotionally to human music rendered in a tamarin style (Snowdon and Teie 2010), and research shows that harbor seals (Verga et al. 2022), cockatoos (Patel et al. 2009), rats (Ito et al. 2022) and chimpanzees (Hattori and Tomonaga 2020) enjoy dancing to human music. In these cases, animals that shouldn’t understand and care about music, or dance, or know that the two are related, unconsciously understand all three things, undermining coevolutionary arguments and supporting a universal sensory bias perspective.

Animals will also dance spontaneously, without a musical cue, in response to the sight of another dancing animal. Campbell (2020) gives an account of chimpanzees playing and joining a group dance featuring spinning in place, forming flowing chains of spinning individuals and trotting with synchronized, asymmetric steps in circles around a pole:

Tschengo and another chimpanzee named Grande invented a game of spinning round and round like dervishes, which was then taken up by all the rest. “Any game of two together,” Dr. Köhler writes, ‘was apt to turn into his “spinning-top” play, which appeared to express a climax of friendly and amicable joie de vivre. The resemblance to a human dance became truly striking when the rotations were rapid, or when Tschengo, for instance, stretched her arms out horizontally as she spun round. Tschengo and Chica — whose favorite fashion during 1916 was this “spinning” — sometimes combined a forward movement with the rotations, and so they revolved slowly round their own axes and along the playground. The whole group of chimpanzees sometimes combined in more elaborate motion patterns. For instance, two would wrestle and tumble near post; soon their movements would become more regular and tend to describe a circle round the post as a center. One after another, the rest of the group approach, join the two, and finally march in an orderly fashion round and round the post. The character of their movements changes; they no longer walk, they trot, and as a rule with special emphasis on one foot, while the other steps lightly, thus a rough approximate rhythm develops, and they tend to “keep time” with one another….’ “It seems to me extraordinary,” Köhler concludes, “that there should arise quite spontaneously, among chimpanzees, anything that so strongly suggests the dancing of some primitive tribes.

Like us, although they have no reason to do so, or to find it amusing, chimps are equipped psychologically with both the desire to dance and the knowledge of how it’s done. Due to the existence of music and dance throughout the animal world, it’s predictable that sensory systems and brains embody an understanding of the qualities and dualities involved automatically, perceive them as opposites and find the idea of mixing them together in intricate patterns intriguing.

Mythology has the same problem with aesthetic themes recurring in widely unrelated cultures and stories that evolutionary biology has with certain themes (song, dance, contrasting colors, ornamental ocelli, long flowing tails, Thayer’s law) turning up in widely unrelated species, and, probably, the same kind of solution in the form of universal preexisting biases in sensory systems. As a potential way to understand common features of human psychology and resulting patterns in mythology, Campbell brought up the subject of sensory bias long before it was popular, in Primitive Mythology (1959), the first volume of The Masks of God series, citing an experiment by Adolf Portmann (1953) with the grayling butterfly, Eumenis semele, which showed that males pursue artificially darkened females “in preference even to the darkest female of the species,” early empirical evidence that animals have preferences for versions of each other that don’t exist in nature:

A new and very promising approach is opened, however, when it [mythology] is viewed in the light of biological psychology as a function of the human nervous system, precisely homologous to the innate and learned sign stimuli that release and direct the energies of nature — of which our brain itself is but the most amazing flower.

Wallin (1991) proposes a kind of sensory bias as the mechanism responsible for the evolution of singing behavior, pointing out the “dynamic dichotomy in music is similar to that which characterizes organismal systems,” and a “morphodynamic isomorphism” between the form of music and that of the brain, music’s physiological substrate.

Sensory bias is usually thought of as a proximal explanation, for instance with the bias ultimately having arisen in an ecological context such as predation and later being exploited by traits that it favors happening to evolve in members of the opposite sex. However, the ecological origin step is an unnecessary complication. Especially when the same bias must have originated repeatedly, and it can’t convincingly be connected to anything of value survival-wise, it’s more reasonable to assume the bias is ultimately an incidental result of the basic structure of the brain to begin with, that it transcends and predates any particular ecological adaptation. Thermoaesthetics hypothetically extends Wallin’s isomorphism beyond music and song to other amusing things such as dance, color patterns and language, by way of a more general isomorphism between the dichotomies of liquid crystalline matter in the brain and aesthetic material.

Perplexity AI

Prompt: “How many species sing songs.”

The number of species that sing songs is far greater than commonly perceived, with conservative estimates suggesting over 200,000 species globally. This includes approximately 4,000 songbird species, at least 200,000 insect species producing vibrational songs, numerous marine mammals, various amphibians, select terrestrial mammals, and an increasing number of documented fish species. The true number continues to grow as researchers discover previously unknown vocal behaviors in species once thought to be silent, revealing that song is a fundamental form of communication across the animal kingdom.

Prompt: “How many species perform courtship dances?”

Conservative estimates suggest that several thousand species across the animal kingdom perform some form of courtship dance. Birds alone contribute hundreds of dancing species across multiple families. When combined with the diverse arthropod dancers, marine species, and representatives from other animal groups, the total likely reaches into the thousands.

Aesthetic Complexity

Primitive perceptual opposites interact in complex ways throughout the history of metaphysical thought.

The unlike is joined together, and from differences results the most beautiful harmony, and all things take place by strife.

— Heraclitus (see Campbell 2008)

Aesthetic phenomena are among the most complex phenomena within the domain of psychology, and this is often used as an excuse by psychologists for being able to say so little about them.

— Daniel Berlyne, Aesthetics and Psychobiology (1971)

Dualities between primitive opposites appear in a suspiciously wide variety of contexts, frequently with qualities from one end of each duality, such as brightness, disorder and fluidity, or those at the other such as darkness, order and solidness, being grouped together as if they’re connected in the mind by default. Cultural, social, philosophical, mythological and religious dualities from around the world, such as those listed below, have almost the same structure as those that delineate primitive sensory systems, particularly with respect to dualities that are also physical opposites in nature.

Cultural dualities: Yin versus Yang in China, Marduk (order) versus Tiamat (chaos) in Mesopotamia, Maat (order) versus Isfet (chaos) in Egypt, Ahura Mazda versus Angra Mainyu or asha (truth and order) versus druj (deceit and chaos) in Iran, Indra (order) versus Vritra (chaos) and Vishnu (order) versus Shiva (chaos) in India, Buddha (calm) versus Mara (chaos), the middle way between dualistic extremes in India, the angel of righteousness versus the angel of evil in the Shepherd of Hermas, Heraclitus’ unity of opposites, the cosmic cycle between order and chaos of Empedocles in Greek philosophy, Aroe (form, stasis, order) versus Bope (flux, dynamism, disorder) in the social structure of the Bororo of Brazil (Maybury-Lewis 1889), the “cyclical oscillation of polar yet complementary opposites” (Maffie 2024) of teotl in Aztec philosophy, Claude Lévi-Strauss’ theory of binary contrast or binary opposition.

In mythology it often happens that primitive opposites weren’t always separate. They split from each other during creation. Bright and dark, order and chaos, and fluid and solid are initially indistinct, cosmologically, just as they actually would have been to animals prior to the evolution of the senses that allow us to tell them apart. Mythological elements split into dualities through the efforts of an original deity, demiurge or some other cosmic force. While cosmological opposite separation might seem like a natural thing to believe in, it isn’t actually that easy to imagine the observations people could have made to give them the impression that some of the opposites most commonly involved in such schemes wouldn’t have always been distinct, as they are now in our nonliving surroundings.

Interactive opposition also appears, arguably, in the ideas of “everything in moderation” and “nothing in excess” (said to be inscribed on the Temple of Apollo), the Buddhist “middle way,” the separation of opposites from Apeiron in the cosmogony of Anaximander, the balance of “love” and “strife” in the cosmic cycle of Empedocles, and the balance between Dionysus, god of wine, pleasure, irrationality and chaos versus Apollo, god of purity, reason and order described in Nietzsche’s The Birth of Tragedy Out of the Spirit of Music (1995).

The Indian concept of Yoga proposes that what we perceive generates a reproduction of itself in the matter of the brain, made possible by the fact that its substance can easily be altered with respect to certain physical qualities. In The Masks of God, Volume 2: Oriental Mythology, Joseph Campbell (2014) translates the definition of the art of Yoga from Patañjali’s Yoga Sūtra, line 1.2, as “the (intentional) stopping of the spontaneous activity of the mind stuff,” implying the brain is in constant motion. Bongiovanni (2018), with “Union” being the meaning of the word “Yoga,” translates the same line a little differently: “Union is restraining the thought-streams of the mind,” as if the motion in the brain is like a fluid. Campbell adds volatility, ripples, brokenness, speed and outwardness to the dynamism and fluidity used to describe the unstoppable motion of the mind:

The archaic psychological theory implied in the definition holds that within the gross matter of the brain and body there is an extremely volatile subtle substance, continually active, which assumes the forms of everything presented to it by the senses, and that by virtue of the transformations of this subtle matter we become aware of the forms, sounds, tastes, odors, and pressures of the outer world. Furthermore, the mind is in a continuous ripple of transformation — and with such force that if one should try without yogic training to hold it to a single image or idea for as long, say, as a minute, almost immediately it would be seen to have already broken from the point and run off into associated, even remote, streams of thought and feeling. The first aim of yoga, therefore, is to gain control of this spontaneous flow, slow it down, and bring it to a stop.

That there’s something subtle and volatile about the brain is undeniable, with this usually being thought to emerge from its complex chemistry, electricity, and/or its numbers of cells and connections, but the contents of language and the analogies we use to describe our minds are usually physical, involving fluidity, motion, disorder, solidness, stillness and geometric shapes, as in the following mind analogy used to explain Yoga, from Campbell (2014):

The analogy is given of the surface of a pond blown by a wind. The images reflected on such a surface are broken, fragmentary, and continually flickering. But if the wind should cease and the surface become still — nirvāṇa: “beyond or without (nir

To the extent that something fleeting, disordered, fragmented or flickering is more exciting than something steady, clear, perfectly formed and quiet, the analogy is a mixture of more and less exciting things. Campbell suggests the qualities of the excited pond are more fun than those of the still pond, and adds that the ability to experience both is ideal.

The Pythagoreans and Alcmaeon

Aristotle says in Metaphysics (1908) that a certain school of “the so-called Pythagoreans” believed the world was composed of ten pairs of opposites, strangely similar to those that differentiate Yin from Yang:

Other members of this same school say there are ten principles, which they arrange in two columns of cognates — limit and unlimited, odd and even, one and plurality, right and left, male and female, resting and moving, straight and curved, light and darkness, good and bad, square and oblong. In this way Alcmaeon of Croton seems also to have conceived the matter, and either he got this view from them or they got it from him; for he expressed himself similarly to them. For he says most human affairs go in pairs, meaning not definite contrarieties such as the Pythagoreans speak of, but any chance contrarieties, e.g. white and black, sweet and bitter, good and bad, great and small. He threw out indefinite suggestions about the other contrarieties, but the Pythagoreans declared both how many and which their contrarieties are.

Alcmaeon is credited with the discovery that the mind resides in the brain, rather than the heart or somewhere else, and the partially true observation that our eyes are filled with fire and water (Huffman 2021). He proposed that “the majority of human things come in pairs” and created an early version of humorism theory: “the equality (isonomia) of the powers (wet, dry, cold, hot, bitter, sweet, etc.) maintains health” while “monarchy among them produces disease.”

The idea isn’t just that too much heat, coldness, wetness or dryness is unhealthy. It’s also that they need to be present in moderate amounts and intricately mixed together to sustain life. Much of what Alcmaeon said happens to be true as a statement about the special physical situation of life, or how we survive by avoiding both freezing into a solid and melting into a fluid.

In the Pythagorean duality system, pairs of opposites are said to be arranged with qualities in the same group being associated psychologically, all of those on one side being “good,” for instance, compared to those on the other, all of which are relatively “bad.” The Pythagorean categories in Greek philosophy are notable because, like Yin versus Yang, they include the duality disorder~order (Huffman 2019):

Opposites played a large role in most Presocratic philosophical systems. The Pythagoreans who posited the table of opposites differed from other early Greek philosophers not only in the normative view of the opposites but also by including strikingly abstract pairs such as straight and crooked and odd and even, in contrast to the more concrete opposites such as hot and cold, which are typical elsewhere in early Greek philosophy.

Straightness, squareness, limitation, stillness, lack of change, singularity, light and right are aligned on the good side for the Pythagoreans, while crookedness, length, freedom, motion, multiplicity, dark and left are supposedly bad. In the practical world, bad things are almost always unwelcome, and we favor the good. Aesthetically, though, bad things are accepted and indispensable; they happen all the time in the interest of providing a contrast to the occurrence of good things. Eliminating them would leave us with a lack of interesting narratives for stories, myths, folklore, literature, plays, movies and so on. Without evil character’s, heroes would have no one to kill. Without an element of disorder art and decoration would be boring, jokes wouldn’t be funny, and music and dance would be almost impossible. In an aesthetic context, neither quality in a pair of opposites is dominant, or necessarily superior. Both are valuable, and almost equally so. One of them, however, in this case evil, disorder, chaos or badness, by whatever name, is fundamentally more exciting than the other, what we might call goodness, order, rightness or peace.

Many other things we normally try to avoid nevertheless play an essential role in aesthetic phenomena. Death and confinement, for example, appear in popular stories at high rates even though in reality we prefer almost exclusively to be alive and free. In these cases we favor qualities on the more exciting side, in contrast to our negative feelings about chaos and evil. Thus, aesthetically, neither higher nor lower excitement is universally “better.” In traditional psychological terms, having a positive valence, or degree of attractiveness, is not consistently the same as being arousing or unarousing, and negative valence isn’t equivalent to high or low arousal either.

The mind being in the brain raises the question of what makes a brain such a suitable substrate for consciousness. Most likely, its condition of extreme physical softness in comparison to other organs and tissues, and other matter, has something to do with how it works. If the complexity of a material is measured by how intimately it mixes fluidity with solidness, the brain is the most complex organ in the body and object in the known universe.

There are probably direct connections between this softness and a brain’s ability to sense stimuli, process information and make decisions. It matters a lot for other body parts to be in a particular physical phase. Blood, bones and teeth didn’t evolve to be liquid and crystalline for no reason. Hearts and other muscles wouldn’t be capable of alternating between relatively relaxed and tense conditions if not for their intermediate and adjustable consistency. Why, then, would we expect that the physical state of the brain is an inconsequential side effect that plays no role in its functionality?

It would be more reasonable to imagine brain softness itself having side effects, perhaps in the form of certain otherwise inexplicable, widespread predilections. The argument also applies to life as a whole. It’s liquid crystalline, rather than liquid or crystalline, and accordingly complicated, with a wide range of both adaptive and nonadaptive consequences, probably including thermoregulation, the need for liquid water and death.

While everything else in the local universe can only change physically in one direction or the other, either into a fluid or a solid, depending on its temperature, life can do both. Robert Frost highlights this in his poem “Fire and Ice,” where he also connects fire to hate and desire, as though it obviously represents these emotions, and the coldness of ice their opposites. He calls death by ice “destruction,” even though burning would be a more destructive way to die than freezing, resulting in an interesting contradiction, an aesthetic effect with the specific structure destruction~ice and the general structure disorder~cold/solid. Overall, the poem expresses in aesthetic form the same idea that Alcmaeon was saying we should consider philosophically, that we can either freeze or melt:

Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To know that for destruction ice
Is also great
And would suffice.

Teotl and Partially Broken Dualities

In the Americas, despite being separated from Greek and Eastern philosophy by thousands of years and living on the far side of the planet, the Aztecs (Mexica) also saw the world in terms of fundamental, interactive opposites. They believed in what James Maffie (2023) describes as a “single, dynamic, vivifying, eternally self-generating and self-regenerating sacred power, energy or force,” which they called “teotl”:

Teotl’s process presents itself in multiple aspects, preeminent among which is duality. This duality takes the form of the endless opposition of contrary yet mutually interdependent and mutually complementary polarities which divide, alternately dominate, and explain the diversity, movement, and momentary arrangement of the universe. These include: being and not-being, order and disorder, life and death, light and darkness, masculine and feminine, dry and wet, hot and cold, and active and passive. Life and death, for example, are mutually arising, interdependent, and complementary aspects of one and the same process. Life contains the seed of death; death, the fertile, energizing seed of life. The artists of Tlatilco and Oaxaca, for example, presented this duality artistically by fashioning a split-faced mask, one-half alive, one-half skull-like (see Markman and Markman 1989:90). The masks are intentionally ambiguous. Skulls simultaneously symbolize death and life, since life springs from the bones of the dead. Flesh simultaneously symbolizes life and death, since death arises from the flesh of the living. The faces are thus neither-alive-nor-dead-yet-both-alive-and-dead all at once.

Life versus the nonliving, in contrast to the ambiguity in teotl, and regardless of a human desire to think otherwise, doesn’t particularly defy metaphysical classification. Being alive is pretty clearly delineated from being dead. The former doesn’t, very much, “spring from the bones” of the later, and live flesh isn’t exactly an unquestionable symbol of death. In other cases, it’s best to accept that there’s a complex middle ground between being only one thing and being two, an indefinite realm where reality almost defies our categories, but they still partially apply, with opposites that are simultaneously conflicting and cooperative.

We don’t have to like that living versus nonliving is a proper duality, or to respect it as such in art and myth. Nothing stops us from creating amusing exceptions like the “neither-alive-nor-dead-yet-both-alive-and-dead all at once” masks of the Aztecs, artificially creating what Maffie calls “dialectical polar monisms.” The similarly ambiguous arrangement between Yin and Yang qualities has been called “dualistic monism.” Here, the phenomenon is simply called a “mixture,” assuming, of course, that one of the participating opposites is, on average, more exciting to the brain and mind than the other.

Ghosts, zombies, vampires, and the rest of the undead are further examples of how the duality of living versus nonliving can be partially broken so that dualistic monism applies. So are immortal beings who die, or have a small, mortalizing defect like the heal of Achilles, or Baldr only being susceptible to a sprig of mistletoe, and the countless gods and characters who die and then come back to life, including Innana in her trip to the ancient Mesopotamian underworld, Odin when he sacrifices himself in the world tree Yggdrasil, and Christ in the crucifixion and resurrection.

Hel, ruler of Hel and daughter of Loki in Norse mythology, is said to be half flesh-colored and half blue, and therefore was probably thought of as both dead and alive at the same time (Crawford 2015, 2018), just like the Aztec masks. It’s a simple detail that makes her more complicated and interesting than she would be otherwise. Dante’s Satan, like Hel, is only half alive in that his lower body is frozen. The circles of hell in Dante’s Inferno overall are reminiscent of Frost’s poem “Fire and Ice,” with punishments ranging from burning in the fiery molten river Phlegethon to being forever trapped in ice. Either way, a person needs to remain alive in some sense, although they’ve supposedly died, in order to experience any kind of hell or other afterlife.

Thermal Dualities in Culture

The idea of a partially broken duality is perhaps most evident in the physics of life, where thermal opposites are caught up in the ultimate dualistic monism, dialectical polar monality, unity of opposites, liquid crystal or mixture of more and less exciting things. In answering the question of whether life is fluid or solid, for instance, it’s not that we’re failing to recognize bodies are actually one or the other, or that life is definitely neither and beyond such metaphysical classification. Life is best described as fluid, solid, both and neither all at once, and this is true of other thermal dualities as well: hot~cold, dynamic~static, disorder~order, all of which are also surprisingly prevalent in philosophical lists of opposites, and unexpectedly likely to be juxtaposed in aesthetic phenomena.

While an appreciation for mixtures of thermal opposites is reflected in the structure of any society, these are particularly clear in what Maybury-Lewis (1989) says about the Bororo of Brazil:

The Bororo… have an all-pervasive dual organization that is at once cosmic, symbolic, and social (see Crocker 1985). It is expressed through the two major classes of spirits that exist in Bororo cosmology: the Aroe and Bope. The Aroe are associated with essence and pure form, as opposed to the Bope who are associated with process and flux. The Aroe are thus static, where the Bope are dynamic. The Aroe are associated with order, the Bope with disorder. The Aroe are comparatively sterile, as compared to the Bope who are associated with both creativity and destruction. The Aroe are rather distant, whereas the Bope are immediate and their influence is both sought and felt.

Fluid qualities (flux, dynamism, disorder) are associated with each other in a mental category, those of the Bope spirits, and solid qualities (form, stasis, order) are grouped together in the concept of the Aroe. The creation of such categories implies associations between those qualities, and consequently a degree of opposition between qualities we don’t normally think of as being opposed, such as destruction versus stasis or motion versus form.

Scientists would have to agree the spirit classes are a suspiciously good description of a liquid crystal, despite having been created by people with no direct knowledge of mesophases or small-scale physics. The same opposites are involved, and arranged appropriately with respect to how they vary thermally. To the extent that flux, dynamism and disorder are perceptually more exciting than form, stasis and order, the Bororo system is a mixture of more and less exciting things. It’s difficult to imagine such a system evolving in the absence of a universal reflex-like preference for a balance between the opposites they apply to the spirits.

Physically, fluid~solid is usually a definitive duality. Few opposites are as clearly demarcated in nature as fluidity versus solidness, or liquid versus crystalline, with the process by which something in one of these states changes into the other normally happening suddenly, at a very specific temperature, assuming invariable pressure. It follows, because matter in a fluid state is disordered and dynamic while that in a solid state is ordered and static, that disorder~order, dynamic~static and other thermal opposites are also definitively dualistic in nonliving matter.

At the same time, however, within living things, especially for brains, these are partly distinct and partly indistinguishable, making bodies and brains impossible to categorize in a dualistic or monistic framework. A brain has the same metaphysical ambiguity as the Aztec masks, being neither-fluid-nor-solid-yet-both-fluid-and-solid all at once, and the same structure as Bororo society, mixing the same qualities into monistic dualities that the Aroe and Bope spirits do.

Aesthetic complexity has thus been recognized and valued for a long time from various otherwise diverse perspectives, by cultures all over the world, since the origins of philosophy, mythology and social structure, continuously so throughout history to the present day, likely because we find it intuitive and amusing, but also because it describes a basic biological reality.

Complexity Theory

Parallels can be drawn between the present thesis and contemporary ideas in complexity theory used to model living systems like the “edge of chaos” (see Lewin 1999) and class four cellular automata. Wolfram (2002) categorizes one-dimensional cellular automata into four distinct classes. Class one, the simplest, tend to collapse rapidly into an infinite fixed state, or an orderly, repetitious pattern. Class two are less regular, developing a slightly more intricate pattern than class one and then repeating the pattern forever. Class three are very random, sometimes running more than a million time steps with no detectable structure, analogous to chaotic systems. The fourth class is special. They were described last, hence the name, but behaviorally they belong between classes two and three.

Class four automata show a mixture of order and randomness that often leads to great complexity, corresponding to the edge of chaos in dynamical systems. Christopher Langton has pointed out that class one and two automata can be taken to correspond to the physical solid state, class three to the fluid state and class four to a phase transition between them (Waldrop 1992).

Under certain sets of rules they yield attractive, complex patterns of order and chaos that resemble those on the surfaces of animals (Wolfram 2002). Recent research (Manukyan et al. 2017) on the “quasi-hexagonal lattice,” “green and black labyrinthine pattern of skin colour” in occelated lizards has shown that “cellular automata are not merely abstract computational systems, but can directly correspond to processes generated by biological evolution.”

Mixtures

Aesthetic phenomena tend to be made up of mixtures of qualities from the more and less exciting ends of primitive perceptual dimensions.

Well did Aristotle say that virtues in contrast to vices are judicious means between contrary extremes. But the principle holds much more generally than even Aristotle saw. It applies, for example, in aesthetic matters. Beauty, too, is a mean. It is not the opposite to ugliness. Ugliness is an incongruity, a disorder, a jolt; but the sheer absence of incongruity and disorder is not beauty. Rather, beauty and all aesthetic value is what, in the words of Kurt Sachs the musicologist, ‘lies between the fatal extremes of mechanism and chaos.’ By ‘mechanism’, understand a too strict and unrelenting orderliness, and by ‘chaos’, a sheer lack of order. In the first case there is too little surprise, sense of tension, or interest in how things may come out; in the second case there are no definite expectations to be met with pleased surprise or to awaken any desire to experience the outcome. With mechanism we are merely bored, with chaos merely confused. In neither way does the sense of beauty arise.

— Charles Hartshorne, Wisdom as Moderation: A Philosophy of the Middle Way (1987)

List 3 below shows the primitive perceptual opposites from lists 1 and 2 as dualities, separated by tildes (~), with the more exciting quality on the left and the less exciting quality on the right. This is meant to emphasize the idea of perceptual opposites occurring in juxtaposition, as what could be called aesthetic mixtures: heat mixed with coldness (hot~cold), fluidity with solidness (fluid~solid), dynamism with stasis (dynamic~static) and so on.

Primitive aesthetic mixtures (list 3): hot~cold, fluid~solid, dynamic~static, fast~slow, disorder~order, bright~dark, warm color (red, orange, yellow)~cool color (green, blue, purple), sound~silence, loud~quiet, high pitch~low pitch, up~down, out~in, left~right, long~round, long~short, spiky~round, big~small, more~less, novel~familiar.

The term “mixture” is borrowed from Galen’s De Temperamentis, “On Mixtures.” His title is a form of the Latin word temperamentum, meaning to be mixed properly, or in due proportion. In Galen’s treatise the physical qualities hot, cold, wet and dry vary in the body and interact to influence a person’s health and disposition, most ideally into an optimal condition of moderation between extremes.

Language-based aesthetic mixtures are essential to the structure of idioms, poetry, lyrics, scripture, slang, clichés, fables, nursery rhymes, chants, prayers, euphemisms, greetings, riddles, jokes, mottos, epitaphs, epithets, kennings, koans, slogans, the names of songs, albums, bands, books, companies and products, and they seem to exist throughout every type of aesthetic material in which linguistic references to phenomena exhibiting animal sensory opposites can appear in pairs or sequences. Nonlinguistic cultural instances of mixtures occur at high rates in music, dance, mythology, fictional stories, art, decoration, games, architecture and elsewhere.

Mixtures also describe traits used to attract mates in animals, which indicates the biases favoring them are universal, and that they originate with sensory systems and persist despite the diversification of other traits, rather than evolving independently or in conjunction with the traits they favor. Thus, mixtures appear in every aesthetic realm, and any particular mixture appears often enough across the realms that if it proves to be common in one of them there’s a good chance it will also be found in others, assuming the respective medium allows it to be conveyed.

Mixtures of up and down can be understood perceptually and expressed visually by almost any animal. Based on its popularity elsewhere, for instance in language, poetry and myth, it’s predictable such motion tends to evolve through mate choice as a feature of courtship rituals. There are conspicuous examples of the mixture up~down in the dances of hummingbirds, bald eagles, red-tailed hawks, nighthawks, skylarks, tropicbirds, American woodcocks, bowerbirds, manakins, cranes, ducks, grebes, grouse, penguins, finches, Anolis lizards, geckos, bearded dragons, Indian dancing frogs, turtles, tortoises, fiddler crabs, mudskippers, stickleback, seahorses, sea dragons, scorpions, fruit flies, mayflies, damselflies, grasshoppers, jumping spiders, peacock spiders and others.

Every aesthetic instance of up~down can be thought of as the effect of a single, universal bias that supports both its origin and persistence, and by the same approach it’s possible to use the popularity of the mixtures out~in, motion~stasis, disorder~order, bright~dark or other mixtures in one type of aesthetic material to predict it’s occurrence in others.

There’s nothing inevitable, based on current evolutionary theory, about the inclusion of mixtures in aesthetic things, which could have any structure, no consistent structure at all, or be avoided altogether with no negative consequences regarding survival. There’s no need for animals to sing songs, let alone songs in which the auditory qualities in list 3 are intricately juxtaposed, or to dance, especially in ways that mix the given dualities of motion and direction, or to be colored in elaborate ways that contrast bright with dark and warm colors with cool colors. Lack of an obvious adaptive purpose is a feature that ties aesthetic things together, which could be taken to suggest the possibility of a single, ultimate explanation for their existence.

Because they were established as opposites early in animal evolution, the qualities in lists 1, 2 and 3 predate other concepts and can be used metaphorically or figuratively in all languages and in the communication of any species that’s capable of making reference to them. All animals understand them by default, and in a similar way, so they make convenient signals.

As a result of the ability to tell the difference between up and down, species have evolved to communicate by moving their bodies, limbs or other features in these directions. Such movements have probably always had meaning to an observer, at least in the sense that upwardness has conveyed a somewhat greater degree of arousal, and downwardness has done the opposite.

At the same time, mixtures of upward and downward orientations and motions have always been intriguing, so that individuals born with genes that compel them to integrate them into their courtship rituals have succeeded disproportionately at reproducing and passed on those genes more effectively than individuals who lack them. This same kind of scenario applies to the other perceptual dimensions of direction, and also to those of motion, color, sound, shape and size.

Mixture frequency, the rate at which mixtures occur per unit of sensory information, with units potentially being words, sounds, colors, shapes, periods of time, movements or other things, is higher in aesthetic material than in non-aesthetic, practical sensory material, such as that used purely to convey important information. Mixture frequencies are higher in a poem, for instance, than a nonfictional report, in a comic routine than a lecture, in a game than a work project, in a mythical or religious text than a science book, or in singing and dancing than speech or the average sequence of motions made in the usual, practical routine of an animal.

Each pair of qualities in list 3 can be thought of in at least three ways: (1) as a primitive duality of differentially exciting opposites in the animal mind, (2) as the structure of a universal psychological bias, and (3) as an essential ingredient in aesthetic phenomena, which evolve to match the structure of the bias. All three perspectives are isomorphic, or structurally similar, in that they incorporate opposites, arguably implying a sequence of causation. Mechanisms of sensation lead to sensory biases, and these biases cause outward aesthetic effects. The mechanism underlying our ability to tell red from blue entails a preference for red~blue mixtures, which is responsible for biological and cultural aesthetic selection favoring their evolution in bodies and artifacts.

Aesthetic isomorphism can be used to predict the contents of aesthetic material, or to identify sensory dualities. We know that all sufficiently visual animals have the ability to distinguish motion from stasis, which allows us to predict that courtship routines and play behavior will alternate between those qualities perceptually. In reverse, we know that fluidity is mixed with solidness aesthetically in creation stories, mythology, poetry and language, and therefore that the duality fluid~solid should be thought of as a primitive perceptual dimension, alongside those we recognize more traditionally as such bright~dark, high pitch~low pitch, up~down and so on. This is also true for disorder~order. Although it’s not normally thought of as a basic sensory dimension, its importance in the structure of aesthetic material tells us that it should be.

Physical qualities in list 3 include Galen’s hot~cold and fluid~solid (wet~dry), as well as dynamic~static and disorder~order. These are of special interest because they represent aesthetic biases that closely resemble the physical dualities that heat, fluidity, dynamism and disorder form with coldness, solidness, stasis and order (see Leslie 2016). The correspondence in this case could be called physical isomorphism, because it extends beyond the realm of biology into state of matter physics. It wouldn’t necessarily be improbable for a physical duality to be isomorphic with an aesthetic one, but there are at least four such corresponding dualities. Others like expand~contract and free~confined could be added to the list, and at some point it becomes difficult to believe the correspondence is coincidental.

The closest psychological idea to that proposed here concerning preferences and excitement might be Daniel Berlyne’s aesthetic model of an inverted-U relationship between pleasantness and arousal. Berlyne demonstrated that both low and high arousal stimuli and mental states are unlikable compared to moderate levels, which are the most pleasing. Likability, or “hedonic tone,” increases from a low point to a maximum for an observer as stimuli become more arousing, before decreasing again as they gradually exceed the observer’s tolerance.

Perceptual variables shown by Berlyne to increase animal arousal levels and vary on a graph of hedonic tone in the shape of an inverted-U include novelty, complexity and surprisingness. In Berlyne’s model complexity as a variable increases with perceptual multiplicity, disorganization, irregularity, incongruity and asymmetry, qualities that might be more accurately described as disorderly than complicated.

Thermoaesthetics hypothetically extends Berlyne’s idea to all primitive perceptual opposites, and assumes the relevant biases for moderation and against extremes have exististed since the evolution of sensory systems, although they can presumably be modified by natural or sexual selection. Hedonic tone is predicted to follow an inverted-U as light level varies for an observer from zero (darkness) to half light to extreme brightness, as pitch moves from low to moderate to high or as the texture of an object changes from solid to soft to wet. In contrast to Berlyne’s perspective, complexity is assumed to correspond to moderate rather than high arousal.

Tildes (~) are used throughout the present text to indicate aesthetic mixtures (list 3), or that the qualities involved are differentially exciting opposites, while slashes (/) or equal signs (=) indicate associations or combinations of qualities in the same psychological category of more or less excitement (list 1 or 2).

Fluid~solid, disorder~order, up~down and out~in are mixtures, for example, while fluid/disorder, fluid/up, fluid/out, solid/order, solid/down and solid/in are combinations. More specifically, with regard to popular expressions, “the land of milk and honey” (fluid~solid), “a diamond in the rough” (disorder~order), “bottoms up” (up~down) and “day in and day out” (out~in) are mixtures, while “break into tears” (fluid/disorder), “hell or high water” (fluid/up), “pissed off” (fluid/out), “a clean slate” (solid/order), “rock bottom” (solid/down) and “come on hard” (solid/in) are combinations.

Conceptual Relatives

Each of the qualities given in list 3 has a number of more specific conceptual relatives that behave the same way the quality does in aesthetic material, presumably because we use primitive sensory opposites as categories into which other, more recently derived phenomena are sorted.

Solidness is essentially the same as hardness, and it’s related in the mind to earth, land, rock, stone, metal, wood, teeth and bone. Fluidity relates to flow, flowers, water, rivers, streams, oceans, smoke, air, clouds, spirals, spirits, souls, ghosts, tears, saliva, breath and blood. Heat relates to the sun, spring, summer and fire, dynamism to wakefulness and life, stasis to sleep, calmness and death, brightness to mornings and day, darkness to twilight and night, high pitch to screaming and singing, low pitch to drums and thunder, spikiness to sharpness, horns, claws, fangs and crosses, roundness to eyes, heads, babies and the moon, length to fingers, tails and snakes, upwardness to being high, over or above, the tops of things, ascent, lifting, climbing and heaven, downwardness to lowness, being on the bottom or below, descent, sinking, falling, dropping and hell.

Simple geometric shapes, symmetry, straightness, regularity, form, patterns, rules, laws, rightness and roundness (spheres, circles, points, spots, dots) are related to the idea of order in the mind, while chaos, crookedness, brokenness, cracks, craziness, asymmetry, disarray, irregularity, the unexpected, strangeness, missing, being wrong, spikiness and length are conventionally disorderly.

We think of something far away or leaving us as outward and something close or coming toward us as inward. The central section of a scene or object is related to inwardness in the mind, while peripheral parts are thought of as outward. We assign inwardness to containers and anything with an inward dimension, such as houses, caves, bags, hats and ships. Behaviors in which something from the outside world enters the body, like breathing in or eating, are also inward, while the expulsion of something from the body is understood as outward. Inwardness applies to our hearts, minds and brains, and entrances to the body, and outwardness to bodily extensions or protrusions such as hands, fingers, feet, noses, hair, wings and tails.

Some of the conceptual relatives corresponding to list 1, 2 and 3 qualities are given for reference below. Because they behave aesthetically in the same way as the primitive qualities they relate to, fire and ice can be juxtaposed amusingly just as heat and cold can. The idea of being clean, a relative or order, is amusingly juxtaposed to being broken, a relative of disorder, in an expression such as “clean break.” The idea of “all” is a conceptual relative of larger numbers of things (many), and it behaves similarly as an aesthetic opposite to the idea of singularity (few), a relative of small numbers, in expressions like “once and for all,” “come one come all” and “all for one and for all.” More exciting qualites are marked with asterisks.

Conceptual Relative Lists

Heat* (34): blaze, blistering, boil, boiling, burn, burning, burnt, char, ember, fever, fiery, fire, flame, furnace, fuse, heat, hot, ignite, inferno, molten, scorch, scorching, simmer, simmering, sizzle, smolder, spark, stew, stewing, summer, sun, swelter, torch, warm.

Coldness (34): arctic, biting, bitter, blizzard, chill, chilled, chilling, chilly, cold, coldness, cool, cooling, crisp, freeze, freezing, frigid, frost, frostbite, frosty, frozen, gelid, glacial, glacier, hail, ice, iceberg, icy, numb, shiver, sleet, snow, snowy, thaw, winter, wintry.

Dynamism* (130): accelerate, action, active, activity, agile, agitate, alter, alteration, altered, animate, animated, awake, awakening, blur, bolt, bounce, bound, burst, bustle, buzz, careen, cascade, change, changing, charge, chase, churn, commotion, current, dance, dart, dash, dynamic, dynamism, electric, energetic, energy, erupt, fast, flail, flap, flicker, flit, flow, fluctuate, flurry, flutter, flux, fly, frantic, frenetic, frenzy, gallop, galvanize, go, gush, haste, hasty, hectic, hop, hurry, hurtle, jerk, jolt, jump, kinetic, launch, leap, life, live, lively, living, momentum, motion, move, nimble, oscillate, play, pulse, quake, quaking, quick, quicken, quiver, race, racing, ran, rapid, restless, rocking, rouse, run, rush, scamper, scramble, scurry, shake, shaky, shift, shock, shudder, skip, speed, speedy, spin, spring, sprint, spun, spurt, stir, streak, stream, surge, sway, swift, swing, swirl, throb, torrent, tremble, tumult, turmoil, twirl, twitch, velocity, vibrate, wake, waking, whirl, whirlwind, whiz, wriggle, zip, zoom.

Stasis (143): anchor, anchored, arrest, asleep, becalmed, buried, bury, calm, chain, check, clamp, coagulate, coma, comatose, constant, corpse, crawl, creep, curb, dawdle, dead, deaden, deadly, death, deathly, die, doldrums, dormant, doze, drowsy, dying, entrenched, equilibrium, fixed, fossil, fossilized, frozen, grave, halt, harden, hibernate, hibernation, hold, hush, idle, immobile, immobility, immovable, immutable, inanimate, indolent, inert, inertia, lag, languid, languor, lazy, lethargic, lifeless, linger, listless, lock, locked, loiter, lull, marble, moor, mortal, motionless, mute, pacify, paralysis, paralyze, pause, peace, peaceful, perish, permanent, perpetual, persist, petrified, pin, pinned, placid, plod, poise, quiescent, quiet, remain, repose, rest, restful, restrain, restrained, rigid, rooted, sedate, sedentary, serene, settle, settled, silence, sleep, sleeping, slack, slow, slumber, sluggish, snooze, solid, somnolent, soporific, stable, stagnant, stagnation, stale, stand, standing, standstill, stasis, static, stationary, statue, stay, steady, stiff, stiffen, still, stillness, stone, stony, stop, stuck, tether, torpid, torpor, tranquil, transfix, trap, unchanging, unconscious, unmoved, unmoving.

Fluidity* (148): air, amorphous, aqueous, bathe, billow, blood, blow, blowing, breath, breathe, breeze, brine, cascade, condense, current, damp, deluge, dew, dissolve, douse, downpour, drain, drench, drift, drip, drizzle, drool, drop, ebb, eddy, ethereal, evaporate, exhale, float, flood, flow, flowing, fluid, fluidity, flush, foam, fog, formless, froth, gale, gas, ghost, glide, gossamer, gush, gust, haze, humid, humidity, immerse, inhale, juice, kiss, kissing, lake, leak, liquefy, liquid, lubricate, melt, melted, melting, milk, mist, moist, moisture, nebulous, ocean, oil, oily, ooze, permeable, permeate, plume, porous, pour, puddle, puff, rain, ripple, runny, saliva, saturate, sea, seep, shower, sigh, sinuous, slick, slide, slime, slip, slippery, slither, smoke, soak, sodden, soggy, soul, spill, spiral, spirit, spit, splash, spout, spray, sprinkle, spurt, steam, stream, submerge, supple, surge, swamp, sweat, swell, swim, tears, thaw, tide, torrent, trickle, undulate, vapor, venom, waft, wash, water, watery, wave, wet, whirlpool, wind, wispy.

Solidness (145): adamant, alloy, anvil, armor, armored, bark, barrier, bastion, bedrock, block, board, bone, boulder, brass, brick, brittle, bronze, buttress, calcify, calcified, carapace, cement, compact, compress, concrete, copper, cornerstone, crystal, crystallize, dense, density, diamond, durable, earth, firm, firmness, fist, flint, fortify, fortress, foundation, frame, frozen, girder, glass, granite, granular, gravel, grit, gritty, ground, hard, harden, hardness, hardy, heavy, hoof, horn, impenetrable, impermeable, inflexible, iron, ironclad, ivory, jaw, keystone, knuckle, land, lead, marble, matter, metal, mettle, mortar, mountain, muscle, nail, oak, obdurate, obsidian, obstinate, ossify, pebble, petrified, petrify, pillar, plank, plate, quartz, rampart, rib, ridge, rigid, robust, rock, root, rugged, scale, shell, shield, skeleton, skull, slab, soil, solid, solidify, solidity, spine, stalwart, staunch, steel, steely, stiff, stolid, stone, stout, strength, strong, stubborn, sturdy, substance, teeth, thick, timber, tooth, tough, toughen, tree, tusk, unbending, unyielding, wall, weight, weighty, wood.

Disorder* (141): anarchy, askew, asymmetric, awry, bedlam, bizarre, blemish, blur, break, broken, cacophony, chaos, chaotic, clash, clutter, confusion, contaminate, corrosion, corrupt, corruption, crack, cracked, cracking, crazy, craziness, crooked, crumble, crumbling, crush, debris, decay, decompose, defect, deform, deformed, demolish, deranged, destroy, destruction, disarray, discord, discordant, disjointed, disorder, disordered, disorderly, disorganized, disrupt, dissonance, dissonant, distort, distorted, entropy, erode, erosion, erratic, error, fault, faulty, flaw, flawed, fracture, fragment, fragmented, fray, frayed, garbled, glitch, gnarled, grotesque, haphazard, havoc, impure, incorrect, irregular, jagged, jarring, jumble, jumbled, lopsided, lunacy, madness, mayhem, mess, messy, mishmash, miss, misshap, mistake, muddle, noise, pandemonium, pollute, ragged, random, randomness, riot, rip, rot, rotten, rough, rubble, ruin, rupture, rust, rusty, scatter, scattered, shatter, shattered, shred, skew, slant, smash, smear, smudge, spatter, splatter, splinter, split, stain, strange, strewn, taint, tangle, tangled, tattered, tear, tilted, torn, twist, twisted, unbalanced, uneven, unhinged, upheaval, uproar, warp, weird, wreck, wreckage, wrong.

Order (120): accord, accuracy, accurate, align, aligned, alignment, arrange, arranged, array, axis, balance, balanced, cadence, calibrate, calibrated, clarity, clean, clear, code, coherence, coherent, concentric, concord, congruent, consistency, consistent, consonance, consonant, correct, discipline, disciplined, equal, even, exact, figure, flat, flawless, form, formula, frame, framework, geometric, grid, harmonic, harmonious, harmony, immaculate, intact, lattice, law, level, line, logic, logical, matrix, measure, measured, method, methodical, neat, norm, normal, order, ordered, orderly, organization, organize, organized, parallel, pattern, patterned, perfect, periodic, perpendicular, polished, precise, precision, principle, pristine, proportion, proportional, pure, purity, ratio, rational, refined, regular, regulate, regulation, repetition, rhythm, right, rule, seamless, sequence, series, settle, settled, shape, smooth, sort, sorted, spotless, square, stable, standard, steady, straight, straighten, structure, structured, symmetric, symmetrical, symmetry, system, systematic, tempo, tidy, true, uniform.

Brightness/Warm Colors* (95): aura, beacon, beam, blaze, blazing, blinding, bright, brighter, brightness, brilliance, brilliant, burnished, candle, color, coruscate, dawn, daybreak, daylight, dazzle, dazzling, effulgent, fire, fireworks, flame, flare, flash, flashes, flashing, garish, glare, glaring, glaze, gleam, gleaming, glimmer, glint, glisten, glister, glitter, glittering, gloss, glow, glowing, gold, halo, illuminate, illumination, incandescent, iridescent, lamp, lantern, light, lighthouse, limelight, lit, lucent, lucid, luminosity, luminous, luster, moonlight, neon, noon, opalescent, pearly, polished, radiance, radiant, ray, reflected, resplendent, scintillate, sheen, shimmer, shimmering, shine, shining, shiny, silver, sparkle, sparkling, splendor, spotlight, star, sun, sunbeam, sunlight, sunny, sunrise, sunshine, torch, twinkle, twinkling, vivid, white.

Darkness/Cool Colors (91): aqua, azure, black, blackened, blackness, bleak, blind, blot, blue, cave, cavern, cerulean, cloak, cobalt, crepuscular, curtain, cyan, dark, darken, darkened, darkening, darkness, dim, dingy, drab, dull, dungeon, dusk, dusky, ebony, eclipse, evening, glaucous, gloaming, gloom, gloomy, gray, green, indigo, inky, jade, jet, lavender, leaden, lightless, mask, matte, midnight, moonless, murky, navy, night, nightfall, obscure, opaque, overcast, penumbra, periwinkle, pitch, purple, sable, sapphire, shade, shaded, shadow, shadowy, shady, shroud, silhouette, slate, smog, somber, starless, stygian, subterranean, sundown, sunless, sunset, swarthy, teal, tenebrous, tomb, turquoise, twilight, ultramarine, umbra, unlit, veil, veiled, verdant, violet.

Loudness/High Pitch* (46): alarm, bang, blare, blast, boom, chirp, clang, clatter, crash, cry, deafening, din, high, high-pitched, howl, loud, loudness, noise, piercing, pitched, resonant, reverberate, ring, roar, rumble, scream, screech, sharp, shout, shriek, shrill, singing, siren, squeal, thunder, treble, twitter, uproar, wail, warble, whine, whistle, yell, yelling.

Quietness/Low Pitch (42): bass, croak, deep, drone, drum, drums, drumming, dull, faint, foghorn, gravelly, groan, growl, grunt, guttural, hoot, hum, hush, low, low-pitched, lull, mellow, moan, muffled, mumble, murmur, mute, muted, purr, quiet, quietness, resonance, rumble, silence, silent, soft, softness, sonorous, subdued, throaty, thunder, whisper.

Upwardness* (53): above, acme, altitude, apex, apogee, arise, ascend, ascendant, buoyant, ceiling, celestial, climb, crest, crown, elated, elation, elevate, elevation, elevated, empyrean, exalted, float, fly, heaven, height, heights, high, higher, hoist, lift, lofty, mount, over, overhead, peak, pinnacle, rapture, rise, rooftop, sky, soar, summit, superior, top, tower, uplift, uplifted, up, upright, upward, upwardness, zenith.

Downwardness (50): abyss, base, beneath, below, bottom, bow, bowed, chasm, collapse, crouch, deep, depth, depths, descend, descent, dip, dive, down, droop, drop, fall, floor, gravity, gulf, hades, hang, heavy, hell, humble, inferior, kneel, low, lower, nadir, netherworld, pit, plummet, plunge, prostrate, sag, sink, slide, slump, stoop, submerge, tartarus, topple, tumble, underneath, underworld.

Outwardness* (69): away, beyond, bloom, blossom, branch, broadcast, burst, cast, dilate, disclose, dispense, disperse, display, disseminate, distend, distribute, effusive, eject, emanate, emit, exhibit, expand, expansive, expel, expose, exposed, express, extend, exterior, external, extrude, exude, exuberant, far, flourish, gape, give, giving, grow, jut, leave, manifest, mushroom, open, opening, out, outer, outside, outward, outwardness, project, projection, protrude, radiate, reach, reveal, shed, show, splay, sprawl, spread, sprout, stretch, swell, tendril, throw, unfold, unfurl, unveil, wing.

Inwardness (53): absorb, brain, burrow, cave, collect, come, conceal, confined, contain, contained, contract, core, cover, curl, deep, depth, door, draw, embrace, enclose, enter, entrance, envelop, fold, gather, get, heart, hidden, hide, hole, hollow, in, ingest, inside, interior, inward, mind, mouth, near, nest, nucleus, pit, pull, receive, root, secret, shrink, sink, swallow, trap, trapped, withdraw, womb.

Long/Spiky* (60): antler, arrow, band, barb, beak, blade, bristle, claw, cord, dagger, elongated, fang, feather, finger, hair, jab, jagged, knife, lance, line, long, needle, pierce, pike, pin, point, pointed, pointy, prick, prickly, prong, quill, ray, ribbon, rod, saber, serrated, sharp, spear, spike, spikiness, spiky, spur, staff, stalk, stem, stick, sting, string, sword, tail, talon, thorn, thorny, thread, tine, tip, tusk, whisker, wire.

Short/Round (57): arc, arch, around, ball, bead, blob, brevity, brief, bubble, bud, bulbous, bulge, cheek, chubby, circle, circular, coil, coin, compact, convex, curve, curved, curvy, curt, disc, dome, dot, dots, drop, dwarf, egg, encircle, eye, globe, head, hemisphere, orb, oval, pearl, pebble, plump, pupil, ring, round, rounded, roundness, seed, short, snub, socket, sphere, spherical, squat, stubby, terse, tiny, truncated.

Large Size* (56): ample, awesome, behemoth, big, breadth, broad, bulky, colossal, colossus, considerable, elephant, enormous, expand, expanse, expansive, gargantuan, giant, gigantic, grand, grandeur, greatness, grow, growing, hefty, huge, hulking, immense, immensity, infinite, large, largeness, leviathan, loom, magnificent, magnitude, mammoth, massive, mighty, monolith, monumental, prodigious, scale, size, sizable, spacious, staggering, stupendous, substantial, super, titan, titanic, tremendous, vast, vastness, voluminous, whale.

Small Size (44): atom, baby, compact, crumb, dainty, diminish, diminutive, dust, elfin, fine, fleck, grain, iota, less, little, meager, microscopic, mini, miniature, minor, minuscule, minute, mite, morsel, mouse, narrow, particle, petite, pinch, scrap, shrinking, slender, slight, sliver, small, smallness, smidgen, snippet, speck, teeny, thin, tiny, trace, wee.

Many* (68): a lot, abundance, abundant, aplenty, army, assorted, bountiful, brimming, bunch, cluster, congested, copious, countless, cram, crammed, crowd, crowded, diverse, endless, flock, full, glut, heap, herd, hoard, horde, host, innumerable, laden, legion, loaded, majority, manifold, many, manyness, mass, mob, more, mound, multiple, multiplicity, multiply, multitude, myriad, numerous, opulent, overflow, packed, pile, plenitude, plentiful, plenty, plethora, plural, profuse, proliferate, replete, rich, richness, several, stack, sumptuous, surplus, swarm, teem, teeming, throng, too much, various.

Few (42): alone, austere, bare, bereft, dearth, deplete, dwindle, empty, few, fewness, gone, handful, isolated, lack, less, lone, minimal, none, one, only, paucity, poverty, rare, rarity, remnant, scanty, scarce, seldom, simple, single, sole, solitary, spare, sparse, spartan, stark, uncommon, vacant, vanish, vestige, void, zero.

Novelty* (45): alien, anomaly, avant-garde, brand-new, curious, cutting-edge, debut, different, enigmatic, exotic, extraordinary, first, foreign, fresh, freshness, ingenious, innovative, invention, latest, mysterious, mystery, new, newness, novel, novelty, odd, original, peculiar, quirky, radical, recent, revolutionary, strange, surprise, uncanny, unexpected, unfamiliar, unheard-of, unique, unknown, unprecedented, unusual, weird, young, youth.

Familiarity (43): again, ancient, antique, archetypal, banal, canonical, classic, cliché, comfortable, common, conventional, cozy, customary, established, everyday, expected, familiar, familiarity, fixed, habit, hackneyed, hoary, home, homely, known, mundane, normal, old, ordinary, recognizable, recognized, remembered, repeated, ritual, routine, same, stale, standard, traditional, typical, unremarkable, usual, worn.

Aesthetic Indifference

Neither the sun nor death can be looked at with a steady eye.

— François Duc de La Rochefoucauld, 1613-1680 (Bartlett 2022)

Nay, I'll come: if I lose a scruple of this sport,
let me be boiled to death with melancholy.

— Shakespeare, Twelfth Night (2022)

Activity conquers cold,
but stillness conquers heat.

— Lao Tzu, Tao Te Ching

Strangely, any mixture of perceptual qualities (list 3) from opposite psychological excitement categories (lists 1 and 2) results in a duality with a structure descriptive of aesthetic phenomena, not only those involving direct opposites.

This works for Somov's painting, contrasting death with the humor of a harlequin, rather than contrasting the direct opposites life and death or humor and seriousness. It also works for the quote from Rochefoucauld, opposing death to the sun instead of life and the sun to death instead of darkness. The quote is amusing because it’s true, in a way, and because of the extreme contrast and differential excitement between the phenomena it refers to. There’s also the suggestion of dynamic stasis, a direct mixture, and of dynamic roundness, another indirect mixture, in an unsteady eye. In Shakespeare’s quote the contrasts are between heat and its indirect opposites sadness and death (hot~sad/static), instead of the direct opposites hot and cold, life and death or happiness and sadness.

One can randomly choose any quality on the more exciting side, from list 1 for instance (or any of its conceptual relatives), juxtapose it with anything on the less exciting side, such as a quality from list 2 (or its conceptual relatives), observe aesthetic material in which the mixture might be conveyed and find that it occurs at an unexpectedly high rate.

Mixing the seven qualities hot, fluid, disorder, bright, dynamic, upward and outward in all possible ways with their opposites results in the set of 49 mixtures given below in list 5. Seven of these are direct opposites, and therefore possible to learn from the outside world, while 42, the majority (~86%), are indirect, and therefore unlearnable, and yet they happen to be almost as important aesthetically as direct opposites, as anyone who looks for them will find.

For simplicity, the “warmer” colors red, orange and yellow could be thought of as types of brightness, and the “cooler” colors purple, blue and green as types of darkness, so that, for instance, anything black and white, red and blue or yellow and green exemplifies the mixture bright~dark (the contrast effect). Also, roundness can be thought of as a type of order, and spikiness and length as types of disorder, justified based on the symmetry versus relative asymmetry of the former compared to the latter. Directly opposite qualities are marked with asterisks.

Direct and indirect aesthetic mixtures (list 4): hot~cold*, hot~solid, hot~order, hot~dark, hot~static, hot~down, hot~in, fluid~cold, fluid~solid*, fluid~order, fluid~dark, fluid~static, fluid~down, fluid~in, dynamic~cold, dynamic~solid, dynamic~static*, dynamic~order, dynamic~dark, dynamic~down, dynamic~in, disorder~cold, disorder~solid, disorder~order*, disorder~dark, disorder~static, disorder~down, disorder~in, bright~cold, bright~solid, bright~order, bright~dark*, bright~static, bright~down, bright~in, up~cold, up~solid, up~order, up~dark, up~static, up~down*, up~in, out~cold, out~solid, out~order, out~dark, out~static, out~down, out~in.*

List 4 doesn’t include mixtures of sound (pitch and volume), left and right, size (big and small), multiplicity (many or few) or novelty. Including these qualities, and treating color as a separate variable from brightness and round~long/spiky as a separate dimension from order~disorder generates a long list of mixtures (324, see Appendix 1), more than it’s convenient to consider at one time, although almost all of them probably correspond to biases and therefore predict the structure of aesthetic phenomena. Examples of mixtures of shape, sound, size and multiplicity are given throughout the text and in Monoaesthetic Mixtures.

Due to aesthetic indifference, the term “mixture” as it’s used here means a juxtaposition between any of the qualities or concepts on the left side of the listed dualities with any of those on the right side. Heat is an opposite of coldness, as usual, but also of solidness, stasis, order and so on. Upward is the opposite of downward, but also of the other less exciting qualities in dimensions of direction: inward, backward, central, the right side, and of every less exciting quality in lists 2 and 3.

Biases for indirect mixtures of up with less exciting directions are largely responsible for the structure of words and expressions such as “up and coming” (generally up~in), “coming right up” (in/right~up), “back up,” “upright,” “freeze up” (cold~up), “hard up” (solid~up), “shape up” (order~up), “stay up” (static~up) and “over night” (up~dark). Upwardness is not present in the literal referents of these expressions. We attach it to them for aesthetic reasons, because it contributes a degree of excitement and satisfying contradiction to an otherwise less exciting quality.

Aesthetic indifference and differential excitement explain the structure of expressions that don’t make sense otherwise. Consider, for example, the idiom “in the cold light of day.” The meaning of the phrase, to consider something carefully, without the interference of strong emotions, has nothing whatsoever to do with temperature or brightness, at least outside the human mind, raising the question of why these qualities are part of the expression. Referencing coldness makes sense because it’s associated with reality, more so than heat. Referencing light and day also makes sense, but for a different reason. They add contradiction and complexity to the expression, making it a mixture, more so than “in the cold dark of night.” With the word “in” at the beginning the phrase has a one to one ratio of more and less exciting things, assuming its specific aesthetic structure is in/cold~light/day (-1-1+1+1=0), and that “day” is a conceptual relative of brightness. If “day” is also treated as a relative of heat, the phrase is slightly more exciting, with the general structure in/cold~light/bright/hot (-1-1+1+1+1=1).

Thermal Indifference

Since all energy used for brain metabolism is finally transformed into heat, intense heat production appears to be an essential feature of brain metabolic activity. 

—Kiyatkin (2019)

As temperature changes in matter, especially within the uniquely narrow thermal window of an animal brain, qualities related physically to fluidity increase or decrease together, and solid qualities do the same in the opposite direction. Within a cell, neuron or brain, every possible pair of fluid versus solid qualities constitutes a pair of opposites, a phenomenon that could be termed thermal indifference.

In a brain, fluidity is as opposite to stasis and order as it is to solidness. Dynamism is as opposite to solidness and order as it is to stasis. Disorder opposes solidness and stasis in addition to order, and this goes for any other fluid and solid attributes, such as freedom versus contraction, or expansion versus confinement. Thermal indifference can be depicted by a set of dualities between direct and indirect opposites related to temperature variation, such as the following, in which direct opposites are marked with asterisks.

Thermal indifference: fluid~solid*, fluid~static, fluid~order, dynamic~static*, dynamic~solid, dynamic~order, disorder~order*, disorder~solid, disorder~static.

Direct opposites might be observed as such in the outside world, and could therefore be learned through experience, although it appears animals understand them as fundamentally different at birth, or soon thereafter. The other dualities listed are indirect, and can’t be as easily learned from the environment because the qualities making them up don’t consistently appear to us as opposites in nature.

That we appreciate these and other unobservable dualities despite a lack of environmental cues from which to conceive of them almost certainly means the mechanism of consciousness is partially thermal and related to liquid crystallinity. The qualities that participate in aesthetic mixtures exhibit the same kind of indifference, and all of the given thermal dualities happen to describe the structure of aesthetic phenomena, an extremely unlikely coincidence that implies a connection between physical conditions in the brain and our sense of beauty, as Leslie (2016) has proposed.

Hue Heat

The Hue Heat Hypothesis (HHH) is based on the idea that light and colours of the environment can affect thermal perception and influence thermal comfort. Specifically, it states that, when spectral power distribution of light reaching an observer’s eye is characterized by long wavelengths in the visible spectrum, the space is perceived as warmer; conversely, when small wavelengths are predominant, the space is perceived as cooler.

— Bellia et al. (2019)

The sensation of heat is unconsciously opposite not only to coldness, but also to the sensation of the color blue, while red feels like an opposite to both blueness and coldness. This is well-established by studies with temperature and color as variables, known as hue heat experiments. Hue heat is one of several results in psychology that demonstrate how we recognize imperceivable dualities, or consider certain qualities to be opposites even though we shouldn’t think of them as such based on experience. It also demonstrates that such dualities can be unconscious.

People will hold a hot blue vessel longer than a hot red one and a cold red vessel longer than a cold blue one (Ziat et al. 2016). Blue coloration counteracts or moderates heat, and red counteracts coldness, meaning hot and blue are indirect opposites in the mind even though we wouldn’t learn this from normal experience, where it’s not true in any obvious perceivable way apart from cultural signals that exploit the associations. It’s only true in the mind and the substance of the brain, and the same goes for cold and red. The fact that people expect a red object to be hotter than an otherwise equivalent blue object, and vice versa, is evidence for mental categories, one of them containing redness and heat and the other blueness and cold, and one could attribute a degree of aesthetic value to the surprise felt by a person discovering the contradiction that red is colder or blue is hotter than they expected.

It’s also been found that red light decreases cold pain thresholds and increases the perceived loudness of louder sounds, or increases sensitivity to higher temperature and sound volume (Landgrebe et al. 2008), and that people feel warmer observing orange than blue (Matsubara 2004, Chinazzo et al. 2017) and in yellow light than blue light (Albers et al. 2015): “Subjects tend to have slightly warmer thermal sensations in yellow light and slightly colder sensations in blue light.” Such studies show we associate the warmer colors red, orange and yellow with each other in a category that is, in a thermal sense, opposite to cooler colors like green, blue, purple and black. Based on loudness making people feel hotter, high volume is likely to be in the hotter mental category, along with brightness and warmer colors, which would explain why we sometimes refer to them as “loud,” and why higher temperature, light and volume are described as upward, which is also on the more exciting side, and their opposites are called downward.

Adding blue to heat or heat to blue creates a perceptual mixture with a sort of moderation, familiarity and interesting complexity that red heat and blue coldness don’t convey. More generally, with cooler colors and black grouped together under the term “dark” and warmer colors and white under “bright,” we favor the mixtures hot~dark and bright~cold over the perceptual, psychological combinations hot/bright and cold/dark. This isn’t just true in an experimental, contact time or latency-based context, but also in poetry, language, fictional stories and mythology, and Gloger’s rule can be interpreted to demonstrate that animals in colder environments prefer more brightly-colored mates while hotter species prefer darker mates.

A simple reason for the hue heat effect is that red, orange and yellow light excite and therefore heat the visual sensory system and brain slightly more than blue light. Assuming that this heat corresponds to some extent with psychological excitement in animals can explain the widespread use of warm colors for warning purposes, and why they so often evolve to characterize courtship signals and sex organs.

There’s plenty of empirical evidence that darker colors like blue are universally related to sadness and redder colors are happier and more provocative, as Clarke and Costall confirmed (2008):

Consistent with the claim by Levy (1984) that cool colors sedate and warm colors provoke active feelings; the present study also found that ‘warm’ colors such as red, orange, and yellow did evoke the more active emotions (by ‘active emotions’ I refer to Levy’s (1984) use of this term when speaking of emotions or feelings that involve physical arousal, and by the use of ‘passive’ those that sedate).

Sounds might feel louder when a person is perceiving red because both redness and loudness increase brain temperature, reinforcing each other to produce an overall less pleasant experience than coldness mixed with loudness or quietness mixed with heat would produce. Most likely, switching one or more quality in the combination hot/loud/bright to its opposite in a perceptual field decreases brain temperature and the overall excitement felt by an observer, while inverting qualities in the combination cold/quiet/dark would increase excitement from a lower point.

It’s predictable that animals have a preference for darker and bluer motion, chaos and fluidity and an aversion for brighter and redder versions of exciting qualities, and that there are corresponding unconscious associations: hot/red/motion/disorder/fluid and cold/blue/stasis/order/solid, with the qualities in each group combining to reinforce each other by way of their common influence on the temperature of the observing animal’s brain. People should be more tolerant or interested in visual brightness and disorder, for instance, when it’s cold or blue than when it’s red or hot, and poetry, myths and dreams, as reflections of the mind, might be expected to incorporate mixtures such as blue~fluid and bright~solid at high rates. Other perceptual dimensions can be added to this scheme, high and low pitch, up and down or out and in, for example, and the same predictions apply, such that high-pitched downwardness and inward brightness are amusing and common in aesthetic phenomena, and so on.

Experiments like those done with temperature, color and sound as variables might be done comparing preferences and aversions for mixtures versus combinations of all primitive perceptual qualities. People should prefer slightly lower pitched sounds, rounder objects and slower movement when it’s hotter and higher pitched sounds, spikier objects and faster movement when it’s colder, for example.

Perplexity AI Research

Perplexity Computer’s response to “Find out if the color red is associated with heat, anger, danger, high arousal and other exciting things.”

Yes — the evidence is extensive and converges from multiple directions. Here’s what the research shows:

Physiological Arousal

Red literally activates the body. Exposure to it increases blood pressure, heart rate, respiration rate, and adrenaline levels, putting the autonomic nervous system into a low-level alert state even when no actual threat is present. Gerard (1958) showed that red light raises blood pressure, respiratory movements, and eye-blink frequency, while blue light decreases all three. A controlled study found that participants rated red-colored images as significantly more arousing than blue ones regardless of whether the content was positive or negative — supporting the “arousal theory of color” that red is arousing per se, not just in context.

Heat

Red is cross-modally linked to warmth. Rooms painted red feel warmer than rooms painted blue at the same actual temperature — a measurable perceptual effect, not just a metaphor. As you’ve already researched with the hue–heat hypothesis, this association is robust enough to influence thermostat behavior and clothing choices.

Anger

The link is both metaphorical and perceptual. A study by Fetterman et al. found that inducing anger makes people more likely to categorize ambiguous color stimuli as red, confirming that “seeing red” is not just an expression but a genuine top-down perceptual bias. Red also primes faster recognition of angry faces compared to gray or blue primes. Cross-linguistically, the ANGER IS HEAT metaphor — which maps onto red — appears in dozens of unrelated languages.

Danger

Red is used for stop signs, fire engines, sirens, and warning flags because its long wavelength makes it one of the most visible colors in the spectrum, and its evolutionary salience (blood, fire, poisonous animals) triggers automatic vigilance. Infants prefer red when primed with a safe (smiling) face but avoid it when primed with a threatening (angry) face, suggesting the danger association is present very early.

Dominance, Aggression, and Competition

At the 2004 Athens Olympics, competitors randomly assigned red uniforms in boxing, wrestling, and taekwondo won significantly more often than those in blue, an effect attributed to red signaling dominance and triggering testosterone boosts in the wearer and intimidation in the opponent. Red also increases impulsiveness, risk-taking, and confrontational behavior.

Sexual Attraction

People wearing red are consistently rated as more attractive by the opposite sex. One hypothesis is that arousal-related blood flow reddens the skin, making the color a signal of sexual receptivity and vitality (Verywell Mind, NC Museum of Art).

Summary

Red is associated with heat, anger, danger, high arousal, dominance, passion, urgency, and sexual attraction — and these are not independent associations. They appear to be bound together by a common thread: red functions as a general intensifier of arousal, and the specific valence (love vs. rage, excitement vs. threat) is determined by context. This is exactly what the color-in-context theory (Elliot & Maier, 2012) proposes and what your “primitive aesthetic mixtures” framework would predict for the hotcold, redblue axis.

Aesthetic Reflex

Leslie (2016) describes the resemblance between physical complexity in the brain and mixtures of fluid qualities with those of solidness in culture. She says something strangely close to what Empedocles said 2,500 years ago, that we somehow understand perceptual fluidity (water, aether), solidness (earth) and beauty (fondness) in terms of similar qualities internally. She proposes a kind of aesthetic reflex between opposites, so that experiencing too much fluidity makes us crave solidness and vice versa:

What if a mode of thought were in intimate connection with phases of matter,… What if the hard form that is crystal, in periods of its prevalence, produced thought that is crystalline? What if an abundance of liquid made thought fluid, or if its absence made thinking desirous of fluidity to combat its parchedness?

This is based on the effectiveness of comparisons between liquid crystal properties and the structure of language, aesthetic material and large-scale social patterns:

Does anything connect the world of liquid crystals’ discovery to the stop-starting rhythm of animation, invented in the same moment, or to the jerkiness of proletarian revolution, which comes only haltingly, … What are the connections between liquid crystals, those in the laboratory and in our devices, and in us, in our bodies and in our thoughts?

It’s not only that fluid thoughts cause solid thoughts and vice versa. It’s also that fluid qualities such as dynamism and chaos cause a desire for stasis and order, and stasis and order for dynamism and chaos. This could be taken to suggest the action of a reflexive, elastic-like mechanism in the structure of the brain, likely a physical one given that the qualities involved are those related to thermophysical variation in matter, especially matter in a liquid crystalline condition. Extremes of other perceptual dualities have the same reflexive tendency. Too much heat makes us desire cold and vice versa. Too much brightness causes a desire for darkness, darkness for light, loudness for quiet and silence for sound, high and low pitch for each other, redder and bluer colors for each other, and more and less exciting things for their opposites in general.

Other Mixtures

While the dualities in list 3 are of interest because they happen to be fundamental and common, there are many more, mostly relatively derived dualities that have similar aesthetic value, and which also seem to be made up of components we think of as opposites with respect to excitement, such as those listed below.

Other aesthetic mixtures (list 5): evil~good, forward~backward, front~back, divine~mortal, life~death, soul~body, happy~sad, angry~content, accidental~deliberate, expansion~contraction, passionate~indifferent, fantasy~reality, dominant~submissive, formless~form, free~confined, loose~tight, open~closed, light~heavy, thin~thick, rough~smooth, future~past, lies~truth, question~answer, rare~common, unknown~known, beginning~ending, everywhere~nowhere, first~last, win~lose, yes~no, affirmation~negation, joy~suffering, you~me, enemy~friend, accusation~apology.

Some of these could be seen as derivatives of more basic dualities. Evil~good might sometimes be interpreted as a specific relative of disorder~order, life~death of dynamic~static and form~formless of solid~fluid. Some could probably be included in list 3 as primitive opposites. Our understanding of light versus heavy and rough versus smooth, for example, might go back as far as or beyond that of spiky versus round. Others, like lies versus the truth and winning versus losing, are clearly more recent conceptions.

These opposites behave the same way as those in list 3, so that anything on the exciting side (written first in each duality) can be coupled with anything on the less exciting side to generate the structure of a common aesthetic theme. Evil versus good and life versus death are derived dualities that have always been popular as juxtapositions in myths and stories, evil and life being more exciting than goodness and death. Ideas of the “good life” and the “evil dead,” therefore, have aesthetic appeal through contradiction that “good dead” and “evil life” do not. We counter the unpleasantness of death by mixing it with life, but also with brightness, redness, fluidity, upwardness, outwardness, evil and divinity, and the unpleasantness of evil with goodness, but also death, darkness, solidness, downwardness and inwardness.

Mixture Direction

(1) Colorless green ideas sleep furiously,
(2) Furiously sleep ideas green colorless.

— Noam Chomsky, Syntactic Structures (1957)

What is ice which gives you fire, and which your fire freezes still more?

— Giacomo Puccini, Turandot

The structure of a mixture can be written with either the more or less exciting quality first, as in hot~cold versus cold~hot or long~short versus short~long. Here they’re mostly written with the supposedly more exciting quality first, although some match the order of occurrence in the aesthetic phenomena they describe.

It’s possible that reversing a mixture will alter its likability and excitingness. Fire~ice might be more intuitive, or congruent with our expectations, and more exciting than ice~fire, for instance, while ice~fire is more surprising, contradictory and moderately exciting, because the initial elements of a sequence automatically come off as more exciting than subsequent elements.

Mixtures in general might show a slight bias on average to fit a preference for excitement going up or down in an experience over time. People might prefer the most surprising or uplifting part of a story, the high-pitched part of a word or the punchline of a joke to happen at its end rather than its beginning, for example.

Inverse Mixtures

Any mixture can be inverted by changing each of its constituent qualities to its opposite. Due to aesthetic indifference, this always results in another mixture, although the inverse of a pair of direct opposites is almost identical to the original, aside from a change in mixture direction. The inverse of dynamic~static is its reverse mixture static~dynamic, which is essentially the same, but the inverse of dynamic~down is static~up, which is very different. The inverse of evil~good is good~evil, almost the same, except that people might like the phrase “good and evil” a little more than “evil and good” or vice versa. Inverting up~good, which would describe God in comparison to the Devil, gives evil~down, a description of the Devil in comparison to God.

It’s typical for both a mixture and its inverse to describe aesthetic phenomena (and corresponding biases), although there’s no traditional theoretical reason to expect this. For instance, biases corresponding to the structures up~dark and bright~down apparently add together in generating selection for vertical color differentiation in visual animals, causing the evolution of darker hues in the upper part of the body and brighter hues below (Thayer’s Law), with the pressure in favor of the overall pattern being stronger than what either bias would contribute by itself. In fact, it’s probably more accurate to say there are four forces at work in this case: the favorable biases up~dark and bright~down, along with those of aversion for the combinations up/bright and dark/down.

The mixture bright~round (with brightness including warmer colors) also describes the structure of ornamental coloration in animals, and so does its inverse long~dark (dark including cooler colors). Here again there are most likely four forces: attraction in mate choice for both of the given mixtures, and aversions for both the combinations bright/long and dark/round.

Biases for mixtures of color and shape have lead, apparently, to brighter and warmer coloration of the head, thorax or abdomen and darker and cooler coloration of the legs and antennae in many insects, and to a prominent pattern observable in birds in which the central, rounder body is brighter and/or warmer in color than the longer, thinner wings. The appeal of the mixtures dynamic~dark and bright~static, along with relative displeasure at the sight of the combinations static/dark and dynamic/bright, are additional biases that likely contribute to the given coloration patterns in birds.

Mixtures of direction and shape, for instance up~round and its inverse long~down, are also typical in animals, across many taxa, and they include extreme cases of sexual traits, where biases are clearly responsible, such as the elevated, rounded train of a dancing peacock or the long, downward tail of a dancing male widowbird.

The mixtures bright~round, long~dark, bright~static, dynamic~dark, up~round and long~down describe aesthetic material in human culture almost as consistently as they do sexually selected traits, indicating both that the preferences are a default condition of the animal mind and that in general they arise in an aesthetic rather than ecological context.

In almost all cases, the inverse of a particular mixture matches an aesthetic pattern that’s nearly as common as the pattern matching the original, including all possible pairs of the given physical opposites: fluid~solid, dynamic~static and disorder~order. This provides evidence in favor of a causal relationship between aesthetic and thermal indifference, and between brain temperature and aesthetic preferences (thermoaesthetics).

Degrees of Relative Excitement

One could assign a positive or negative value, most simply either 1 or -1, to each quality in a perceptual pattern and add them together to estimate the degree to which the pattern should, hypothetically, excite an observer or influence temperature in the brain. Such values and their sum could be called “degrees” (deg) with positive values corresponding to more excitement, negative values to less and intermediate amounts to mixtures, perceptual complexity and aesthetic (hedonic) value.

This system isn’t meant to imply that brain temperature is altered by 1 degree in response to list 1 qualities or by -1 in response to list 2 qualities. Seeing red probably results in a greater increase in brain temperature than seeing blue, for instance, but not, of course, in an increase of exactly two degrees or any amount corresponding to a particular integer, and the perception of cool colors might increase brain temperature, but slightly less so than warm colors. Biological and cultural patterns can be used to predict relative changes in brain temperature in response to various perceptions, not the absolute quantity of degrees of change, although these can presumably be measured in practice, compared and discovered to either support or oppose the present thesis.

If a quality can be shown to be more exciting than what we would typically think of as its opposite, it has positive degrees of excitement regardless of how we feel about it otherwise. Units of degrees reflect excitement levels, not our opinions about whether something is good or bad. Both gods and devils, being divine, would be assigned a positive degree even though most people would normally call the latter negative. Anger, also, which we would normally call a negative emotion, has a positive degree of excitement because it’s an exciting experience, regardless of how much we like it.

Any mixture (defined as a juxtaposition of differentially exciting perceptual qualities) involving only two qualities would have zero total degrees of excitement (deg=0). Any combination of two qualities from the exciting side, both with 1 degree, will have 1+1=2 degrees overall. Combinations of two less exciting things would be doubly unexciting, deg=-2.

Many phenomena exhibit more than one quality simultaneously. A rock is both solid and static (-2 deg). The sun is hot, bright, yellow, upward and round (1+1+1+1–1=3 deg), making it more exciting than a rock by about 5 degrees. The rising sun (up/bright=2) is exiting compared to the setting sun (down/bright=0). The moon is upward, solid, sometimes bright, other times dark, sometimes spiky and other times round (1–1+1–1+1–1=0), or complicated and moderately exciting by comparison to the sun or a rock. A waterfall (fluid/dynamic~down=1) is slightly exciting, but balanced by downwardness relative to a geyser (fluid/dynamic/up=3), or a volcanic eruption (up/hot/bright/dynamic=4). An animal is both static and dynamic, fast and slow, noisy and quiet, long and round, inward and outward, and so on, making it an unusually complex mixture, and one can imagine some of this complexity having evolved to fit that of sensory systems.

This system is an oversimplification in that the actual amount of excitement felt by an observer varies between qualities. The color yellow, although it’s assigned a value of 1, the same as red, should in reality be somewhat less exciting, green more so than blue, and so on with other colors, green actually being close to neutrality. The excitement attached to qualities perceived with different sensory systems or subsystems in the same modality can’t actually be equivalent. Outwardness might be more exciting than upwardness, downward less so than inward or vice versa. In fact, there’s linguistic evidence to conclude visual qualities are generally more exciting than auditory ones, which themselves are more exciting than olfactory ones.

Various species appear to have evolved to exploit the fact that brains combine the effects of more exciting qualities, using bright and redder coloration, length, spikiness, high pitch, large numbers and other list 1 qualities to discourage predators, the frightening experience of a swarm of bees (many/bright/high pitch=3) or a long, hissing, spitting snake (long/high pitch/fluid/out= 4) being examples. Employing these combinations would be a convenient evolutionary strategy because it should work to some extent on any adversary.

Humans tend to make references to the same frightening qualities when we’re angry. As phrases about anger from “sources across the web,” Google lists the top five as “fuming” (hot/fluid=2), “ballistic” (dynamic/up/out=3), “red” (redness=1), “drive someone crazy” (dynamic/disorder=2) and “blow a fuse” (disorder/hot=2). “Blow your top,” “fly off the handle” and “pissed off” are also in the list, with the respective structures disorder/up=2, up/out=2 and fluid/bright/out=3.

Notably, multiplication of less exciting things increases their perceptual excitingness. This would explain why, in animals with sexually selected spots, the spots are typically dark, and why the cultural, fictional multiplication of eyes and heads (many~round) is so common, as well as traditional religious expressions that repeatedly mention inwardness like “Holy of Holies,” “Holiest of Holies” or the chant of the four beasts that go around with God in the Bible (Coogan et al. 2018):

And the four living creatures, each of them with six wings, are full of eyes all around and inside. Day and night without ceasing they sing, “Holy, holy, holy, the Lord God the Almighty, who was and is and is to come.”

A red (deg=1) and blue (deg=-1) phenomenon (1–1=0) is intermediate, neutral and complicated excitement-wise relative to a red and yellow (deg=1+1=2) or blue and purple (deg=-1–1=-2) object. A black (-1) and white (+1) pattern is more complicated than pure black (-1) or white (1), and it happens to be widely characteristic of both animals and aesthetic artifacts: orcas, pandas, penguins, zebras (and numerous animals with “zebra” in their name), tuxedos, soccer balls, piano keys, chess boards, chess pieces, the Yin Yang symbol and so on. The black~white pattern in animals is often emphasized and displayed to mates in courtship routines, in which cases it evolved to explicitly satisfy a bias. In octopuses it can be a dynamic pattern in which a male turns pale and flashes black stripes across its body to impress a female.

A song-like sequence of sound mixing high pitch with low pitch (1–1=0) and/or sound with silence (1–1=0) is intermediate and complex relative to uninterrupted high-pitched noise (+2), uninterrupted low-pitched noise (-1) or silence (-1), and language is the same way, with extremely complicated variation in pitch and loudness, particularly so in poetry.

Distortion (+1) of a perfect geometric grid (-1) results in a pattern with an intermediate degree of excitement, 1–1=0. Reshaping a perfectly round or spherical shape to be somewhat elongated or spiky results in a more moderate and complex experience for the observer, which is almost certainly why eggs, flower petals and ornamental ocelli are this way (see Disruptions of Roundness). Reshaping it further, into an extremely long or spiky form, makes it exciting beyond what animals prefer.

Due to aesthetic indifference, any higher degree quality or concept can interact aesthetically with any lower degree quality or concept, not only its direct opposite. The mixtures long~round and red~round both have 0 degree structures, and so does long~dark, while long redness is more exciting (2 deg) and dark roundness is less so (-2 deg). As a result, sexually selected patterns throughout the animal kingdom tend to be characterized by the former structures. Up~dark and down~bright are zero degree structures while down/dark and up/bright are offset from zero by 1 degree, thus animals are likely to be darker dorsally and brighter ventrally (see Painted by Nature).

It’s common for a single, given aesthetic pattern, such as a poem, to incorporate alternating references to more and less exciting phenomena, creating an amusing rhythm that adds up to 0 or nearly 0 total degrees. Consider the famous quote from Shakespeare’s Romeo and Juliet (2022):

Why, then, O brawling love! O loving hate!
O any thing, of nothing first create! [anything~nothing (many~few, deg=1–1=0)]
O heavy lightness! serious vanity! [light~heavy (deg=1–1=0)]
Mis-shapen chaos of well-seeming forms! [disorder/disorder~good/order, deg=1+1–1–1=0]
Feather of lead, bright smoke, cold fire, [hot/bright/fluid/light~cold/heavy (deg=1+1+1–1–1=1)]
sick health!
Still-waking sleep, that is not what it is! [dynamic~static/static (deg=1–1–1=-1)]
This love feel I, that feel no love in this.
Dost thou not laugh?

Three of the nine lines have 0 degrees of excitement, one line has 1 degree and one has -1, resulting in deg=0 overall. These aren’t necessarily all the mixtures present. Hate could be more exciting than love, health more than sickness (or vice versa), vanity more than seriousness, brawling, hate and love more than “O” and laughter and love more than negation in “not laugh” and “no love.” Adding these mixtures still results in 0 total degrees for the lines. Shakespeare is listing contradictory opposites here, and many of the opposites he chose are those from list 3.

General Scraps