On Sense Perception (Theophrastus)

PART I. THE SENSORY PROCESS
The various opinions concerning sense perception, when regarded broadly, fall into two groups. By some investigators it is ascribed to similarity, while by others it is ascribed to contrast: Parmenides, Empedocles, and Plato attribute it to similarity; Anaxagoras and Heraclitus attribute it to contrast.

The one party is persuaded by the thought that other things are, for the most part, best interpreted in the light of what is like them; that it is a native endowment of all creatures to know their kin; and furthermore, that sense perception takes place by means of an effluence, and like is borne toward like.

The rival party assumes that perception comes to pass by an alteration; that the like is unaffected by the like, whereas opposites are affected by each other. So they give their verdict for this [idea of opposition]. And to their mind further evidence is given by what occurs in connection with touch, since a degree of heat or cold the same as that of our flesh arouses no sensation. Such then are the teachings handed down to us with regard to the general character of sense perception. As for the various senses severally, they are almost wholly neglected by these authors —save Empedocles, who tries to refer also the particular senses to similarity. Parmenides gives no definition whatsoever, saying merely that there are two elements, and that our know ledge depends upon the excess of one or the other. For according as the hot or the cold predominates does the understanding vary, there being a better and purer understanding derived from the hot; yet even such knowledge requires a certain proportion. "For ever as it finds the blend in their far wandering members," he says, "so does mind come to men; for that which has intelligence in men each and all is the same,—the substance of their members; since what is there in greater measure is their thought."

For to perceive by the senses and to have intelligence are treated by him as identical; consequently both remembering and forgetting arise, by the mixture [of the elements mentioned]. But if there should occur an exact equality in the mixture, he does not make it clear whether there would or would not be thought, nor what would be the general state [resulting]. But that he also attributes perception to the opposite [element] in its own right is evident from the passage where he says that a dead man—since now the fire has left him—does not perceive light and warmth and sound, but does perceive cold and silence and the other contrasting qualities; and that absolutely all being possesses some power of knowing. Accordingly by this thesis he seems arbitrarily to preclude discussion of the difficulties attending his position. Plato " gives greater heed to the senses severally, yet he actually does not speak of them all, but only of hearing and sight.

[The organ of] vision he makes to consist of fire; (and this is why he regards colour also as a flame given off from bodies, having particles commensurate with the organ of vision); h assuming then that there is this effluence and that [effluence and organ] must unite, he holds that the [visual stream] issues forth for some distance and coalesces with the effluence, and thus it is we see.js His view, consequently, may be said to lie midway between the theories of those who say that vision falls upon [its object]l and of those who hold that something is borne from visible objects to the [organ of sight].

Hearing he defines in terms of sound: for sound is a blow given by the air to the brain and blood, through the ears, and transmitted to the soul; the motion caused by this blow and extending from the head to the liver is hearing.

Of smell, taste, and touch he tells us nothing whatever, nor does he say whether there are any other senses than these [five]. He undertakes a more accurate account, however, of the objects of these senses.

Empedocles has a common method of treating all the senses: he says that perception occurs because some thing fits into the passages of the particular [sense organ]. For this reason the senses cannot discern one another's objects, he holds, because the passages of some [of the sense-organs] are too wide for the object, and those of others are too narrow. And consequently some [of these objects] hold their course through without contact, while others are quite unable to enter. Then he attempts to tell us the character of the organ of vision. Its interior, he says, is of fire; while round about this [internal fire] are earth and air, s through which the fire, by reason of its subtilty, passes like the light in lanterns. The passages [of the eye] are arranged alternately of fire and of water: by the passages of fire we perceive white objects; by those of water, things black; for in each of these cases [the objects] fit into the given [passages]. Colours are brought to our sight by an effluence. Yet [eyes, he holds,] are not all of like construction from these opposing elements: in some [eyes] the fire is at the centre, in others it lies more external. Because of this, certain animals see better by day, others by night: by day those whose eyes contain less of fire [have an ad vantage]; for with them the light within is made equal [to the water within the eye] by the [light] without. But those whose eyes have less of the opposite [element I—their vision excels] by night; for with them, also, their lack is supplied [from without]. But reverse the conditions, and the opposite is true: for now even the animals that have fire in excess are dim of sight [by day], since the fire within—increased still further by the daylight — covers and occupies the passages of water. And the same thing happens by night to those with water [in excess], because the fire is now overtaken by the water. This goes on until for the one group the [excessive] water is cut off by the outer light; and for the other, the [excessive] fire is cut off by the air. Thus each finds its remedy in its opposite. But that [eye] is of happiest blend and is best which is composed of both [these constituents] in equal measure. This represents fairly well what he says of vision. He says that hearing results from sounds within [the head], whenever the air, set in motion by a voice, re sounds within. For the organ of hearing, which he calls a " fleshy off-shoot ", acts as the ' bell ' of a trumpet, ringing with sounds like [those it receives]. When set in motion [this organ] drives the air against the solid parts and produces there a sound.

Smell, according to Empedocles, is due to the act of breathing. As a consequence, those have keenest smell in whom the movement of the breath is most vigorous. The intensest odour emanates from bodies that are subtile and light. Of taste and touch severally he offers no precise account, telling us neither the manner nor the means of their operation,—save the [assertion he makes with regard to all the senses in] common, that perception arises because emanations fit into the passages of sense. Pleasure is excited by things that are similar [to our organs], both in their constituent parts and in the manner of their composition; pain, by things opposed.

In a like strain he speaks also of understanding and of ignorance. The one is due to what is like; the other to what is unlike; since in his view thought is either identical with sense perception or very similar to it. For after enumerating the ways in which we recognize each element by its like, he finally adds: " For from these have all things been fittingly conjoined, and by their means do creatures think and have delight and suffer grief." Accordingly, we think chiefly with the blood; for here the elements are more fully mingled than in any other of our members.

Those in whom these mingled elements are of the same or nearly the same [amount], being neither widely separated nor too small nor of excessive size,—such persons are most intelligent and keen of sense; and others are intelligent and keen of sense according as they approach to such a mixture; but those whose condition is the very reverse are the least intelligent. Again, persons in whom the elements lie loose and rare are slow and laborious; while such as have them compact and divided fine are impulsively carried away; they throw themselves into many a project, and yet accomplish little, because of the impetuous coursing of their blood. But when the composition in some single member lies in the mean, the person is accomplished in that part. For this reason some are clever orators, others artisans; for in the one case the happy mixture is in the tongue, in the other it is in the hands. And the like holds true for all the other forms of ability.

Such is Empedocles' theory of the process both of sense perception and of thought. Yet from his account we might well be at a loss to know, first, wherein animate beings differ from other kinds of being so far as sense perception is concerned; since particles fit into the minute passages in lifeless objects also. For universally he regards mixture as due to a correspondence with these passages. This explains why oil and water will not mix,— in contrast to other fluids and to certain farther substances of which he recounts the peculiar combinations. Wherefore all things would perceive; and mixture, sense perception, and growth would be identical (for he ascribes them one and all to a correspondence with the passages), unless he add some farther difference.

In the second place, with regard even to animate things, why should the fire within the living creature perceive, rather than the fire without, if each really fits into the other? for [on both sides] there is proportion and likeness. And further there must be some difference between the two if the [fire within] is unable to fill up the passages, while the [fire] entering from without [has this power]. Consequently if [this internal fire] were absolutely and in every respect the same [as the fire without], there would be no perception. Furthermore, are these passages empty or full? If empty, Empedocles is inconsistent; for he says that there is absolutely no void. But if full, creatures would perceive perpetually; for it is evident that a [substance] similar [to another]—to use his own expression—fits [into that other].

And yet doubt might be felt upon the very point,— whether it were possible for diverse elements to be of precisely a size to fit each other; especially if it be true, as he says, that eyes with some disproportion in their mixture become dim of sight by a clogging of their passages, now with fire and now with air. Granting, however, that there is even here a nice adjustment, and that the passages are filled by what is alien, yet how and where are these [occluding particles] to be expelled when perception occurs? Some change must be assigned. Thus there is a difficulty in any case: for it is necessary to assume either the existence of a void, or that creatures are uninterruptedly perceiving things; or else that an alien substance can fit into [the sensory passages] without causing perception and without involving the change peculiar to the substances that do cause perceptions.

But, further, were we to suppose that what is like does not fit [the passages] but merely touches [there], perception might reasonably arise from any source whatever. For he attributes our recognition of things to two factors—namely, to likeness and to contact; and so he uses the expression " to fit ". Accordingly if the smaller [particle] touched the larger ones, there would be perception. And likeness also, speaking generally, is out of the question, at least according to him, and commensurateness alone suffices. For he says that substances fail to perceive one another because their passages are not commensurate. But whether the emanation is like or unlike [the sensory organ] he leaves quite undetermined. Consequently either perception is not dependent on similarity; or else the failure to detect an object cannot be attributed to want of spatial correspondence, and the senses without exception and all the objects they perceive must have one and the same essential nature.

Moreover, his explanation of pleasure and pain is inconsistent for he ascribes pleasure to the action of similars, while pain he derives from opposites. For these, he says, are " hostile ", since " most distant they stand from one another . . . in source and composition and in their moulded forms." s

Pleasure and pain thus are regarded by them as sense perceptions or as accompaniments of sense perception; consequently [the perceptive process] does not in every case arise from similarity. Again, if kindred things especially cause pleasure by their contact, as he says, things which coalesce in their growth should have the keenest pleasure,—and, in general, the keenest perception [of one another], for he assigns the same causes for sense perception as for pleasure. And yet when we are perceiving, we often suffer pain in the very act of perception,—indeed, Anaxagoras declares, we always do. For all perception, he says, is linked with pain. A like difficulty appears in connection with the senses severally; for his position is that cognition is due to likeness. Now since, for him, the eye is composed of fire and of its opposite, it might well recognize white and black by means of what is like them; but how could it become conscious of gray and the other compound colours? For he assigns [their perception neither to the minute passages of fire nor to those of water nor to others composed of both these elements together. Yet we see the compound colours no whit less than we do the simple.

Odd, too, is [his account of] the fact that certain animals see better by day, and others by night. For a weaker fire is extinguished by a stronger; s and for this reason we find it impossible to gaze at the sun or at anything exceedingly bright. Accordingly animals with less of light in their eyes ought to have had poorer vision by day. Or if what is qualitatively similar does in fact supplement, and what is qualitatively different tends to destroy and thwart, as he says, then all creatures—both those that had less light and those that had more—should have seen white things better by day; and black, by night. Yet in fact all but a few animals see every manner of object better by day. And for these exceptional animals], we may reasonably suppose, the fire inherent in their eyes is peculiarly intense; s just as some objects by their own colours glow brighter in the night.

In those cases, moreover, where the blend is in equal measure, each component would of necessity be supplemented in turn. And consequently if an excess of the one element prevented the other from seeing, all creatures would to all intents and purposes be in a like condition.

Although it is a fairly difficult task to explain the facts of vision, yet how could we by likeness discern the objects with which the other senses deal? For the word ' likeness ' is quite vague. [We do] not [discern] sound by sound, nor smell by smell, nor other objects by what is kindred to them; but rather, we may say, by their opposites. To these objects it is necessary to offer the sense organ in a passive state. If we have a ringing in the ears, or a taste on the tongue, or a smell in the nostrils, these organs all become blunted; and the more so, the fuller they are of what is like them,—unless there be a further distinction of these terms.

Next, as to the effluences. While his account, in the case of the other senses, is inadequate, yet it is, in a way, intelligible; but his thought is indeed difficult to follow when it comes to touch and taste. How can we discern their objects by an effluence; or discern the rough and the smooth as fitting into the sensory passages? For it would seem that, of the various elements, there is an effluence only from fire, but not from any of the others. Also if effluence involves a loss of substance—and this he uses as a universal testimony [for his theory] —and if it be true, too, that odours arise through effluence, then those substances with the strongest odour would most rapidly perish. Now the fact is nearly the reverse: the most fragrant plants and other bodies that are most odorous are the most enduring. In all consistency, moreover, at the time of Love, s there should be no sensory perception at all, or at least less than usual; because under such circumstances recomposition and not effluence would be taking place.

Again, with regard to hearing, it is strange of him to imagine that he has really explained how creatures hear, when he has ascribed the process to internal sounds and assumed that the ear produces a sound within, like a bell. By means of this internal sound we might hear sounds without, but how should we hear this internal sound itself? The old problem would still confront us.

Odd, too, is the account he gives of smell. In the first place, he does not assign a cause which applies to all cases, since some animals that have a sense of smell do not breathe at all. Secondly, it is silly to assert that those have the keenest sense of smell who inhale most; for if the organ is not in health or is, for any cause, not unobstructed, mere breathing is of no avail. It often happens that a man has suffered injury [to the organ] and has no sensation at all. Furthermore, persons 'short of breath or at hard labour or asleep —since they inhale most air—should be most sensitive to odours. Yet the reverse is the fact. For in all likelihood respiration is not of itself the cause of smell, but is connected with it incidentally; as is shown in the case of other living creatures as well as by the facts just recounted. But as though setting his hand and seal to the thought that it is the cause, he says again in closing, “In this wise have they all received as their portion both breath and odours."

Nor is it true that light bodies most strongly affect the sense of smell; nay [in addition to the lightness] there must actually be some odour resident [in the bodies]. For air and fire are the very lightest of substances, and yet produce in us no sensation of odour.

One might likewise have serious misgivings over his doctrine of thought, if Empedocles actually regards thought as having the same constitution as sense; for then all [creatures] would share in thought. And how can the notion be entertained that thinking arises in a process of change, and at the same time arises by the agency of the like? since the like produces no change in the like. And it is indeed quite ridiculous to suppose that we think with the blood: for many animals are bloodless; and of those that have blood, the parts about the organs of sense are the most deficient in blood. Furthermore, according to his view, bone and hair ought to perceive, since they too are composed of all the elements. In all consistency, moreover, to think and to perceive and to enjoy would be identical processes; and, on the other hand, to suffer pain and to be ignorant,—for these two he ascribes to unlikeness. Accordingly, pain ought to accompany ignorance; and pleasure, the act of thinking.

Again, his idea is odd that the special abilities of men are due to the composition of the blood in their particular members,—as if the tongue were the cause of eloquence; or the hands, of craftsmanship; and as if these members did not have the rank of mere instruments. Indeed one might better for this reason assign the shape of the organ as the cause [of talent]; rather than ascribe this to the composition of the blood [in the organ],—which really has nothing to do with understanding. For this is the case certainly with animals other [than man]. Empedocles thus seems to have gone astray at many a point. Of those who ascribe perception to something other than similarity, Alcmaeon states, to begin with, the difference between men and animals. For man, he says, differs from other creatures "inasmuch as he alone has the power to understand. Other creatures perceive by sense but do not understand "; since to think and to perceive by sense are different processes and not, as Empedocles held, identical. He next speaks of the senses severally. Hearing is by means of the ears, he says, because within them is an empty space, and this empty space resounds. & A kind of noise is produced by the cavity, and the internal air re-echoes this sound. Smelling is by means of the nostrils in connection with the act of respiration when one draws up the breath to the brain. By the tongue we discern tastes. For since it is warm and soft, the tongue dissolves [substances] with its heat; and because of its loose and yielding texture it readily receives and transmits [the savours].

Eyes see through the water round about. And the eye obviously has fire within, for when one is struck [this fire] flashes out. Vision is due to the gleaming,— that is to say, the transparent—character of that which [in the eye] reflects the object; and sight is the more perfect, the greater the purity of this substance. All the senses are connected in some way with the brain; consequently they are incapable of action if [the brain] is disturbed or shifts its position, for [this organ] stops up the passages through which the senses act. Of touch he tells us neither the manner nor the means of its operation. So far and no farther, then, does Alcmaeon's discussion carry us.

Anaxagoras holds that sense perception comes to pass by means of opposites, for the like is unaffected by the like. He then essays to review each sense separately. Accordingly he maintains that seeing is due to the reflection a in the pupil, but that nothing is reflected in what is of like hue, but only in what is of a different hue. Now with most [creatures] this contrast of hue [with that of the pupil] occurs by day, but with some by night, and this is why the latter are keen of vision by night. But, in general, night the rather is of the eye's own hue. Furthermore, there is reflection by day, he holds, because the light is a contributing cause of reflection, and because the stronger of two colours is regularly reflected better in the weaker. Touch and taste, according to Anaxagoras, perceive their objects after this same manner. For what is of the same degree of warmth or of cold [as another object] does not warm or cool [this other object] upon approaching it; and certainly we do not become aware of the sweet and of the sour by means of these qualities themselves. On the contrary we come to know the cold by the hot, the fresh and fit to drink by the brackish, the sweet by the sour,—according as we are deficient in one or another of these; although, as he says, they are all present in us.

And similarly of smell and hearing: the former accompanies inhalation; the latter depends upon the penetration of sound to the brain, for the enveloping bone which the sound penetrates is hollow. All sense perception, he holds, is fraught with pain, —which would seem in keeping with his general principle, for the unlike when brought in contact [with our organs] always brings distress. This is illustrated by [our experience when an impression] long persists and when the exciting objects are present in excess. For dazzling colours and excessively loud sounds cause pain and we cannot long endure the same objects. The larger animals have more perfect powers of sense, and sense perception varies in general with the size [of the organs of sense]. For animals that have large clear lustrous eyes see large objects and such as are distant; while of animals with small eyes the opposite is true.

And likewise of hearing. For large animals hear loud sounds and sounds far away, and the more minute sounds escape them; while small animals hear sounds that are minute and close at hand. And similarly of smell: for rarefied air has a stronger odour, since it is odorous when heated and rendered less dense. A large animal when breathing, accordingly, inhales the dense along with the subtile, while the small animal inhales merely the subtile; large animals as a consequence have the more perfect sensory power. For an odour near by is more intense than one remote, he holds, because it is denser, and in scattering becomes faint. Roughly, then, his view is, that large animals perceive no ' subtile odour ', and small animals no odour that is dense.

Now there is a certain reasonableness, as I have said, s in explaining sense perception by the interplay of opposites; for alteration is held to be caused, not by similars, but by opposites. And yet even here one might entertain a doubt whether sense perception actually is an alteration, and whether an opposite is cognizant of its opposite. But as for the thesis that sense perception is universally conjoined with pain, this finds no warrant in experience, inasmuch as some objects are actually perceived with pleasure, and most of them at least without pain. Nor is it reasonable. For sense perception is in accord with nature, and no such process does violence and brings pain, but the rather it has pleasure as its accompaniment,—a law whose operation is quite manifest. For as a rule we take pleasure in things, and perception itself is some thing sought by us, apart from any desire we may have for the particular [object perceived].

Moreover since pleasure and pain alike arise from sense perception, and yet all that accords with nature tends to produce good rather that evil —as is the case also with the knowledge process,—[perception] would be linked more intimately with pleasure than with pain. In a word, if understanding is not painful, clearly sense perception is not; for they both stand in the same relation to the same [kind of] need. Nor does the effect of excessively intense stimuli and of stimulation long continued prove that perception is [invariably] conjoined with pain, but rather that sense perception implies a certain correspondence and a composition suited to the object. And this perhaps is why a deficient stimulation passes unperceived, and an excessive one causes pain and is destructive. Now our author, we see, arrives at his interpretation of what is normal and according to nature, from what is exceptional and contrary to nature; for excess is contrary to nature. For it is patent and not to be denied that we receive pain now and then from various sources, even as we do pleasure. Upon this showing, consequently, [perception] is no more invariably connected with pain than with pleasure, but in strict truth is inseparably connected with neither. For, like thought, [perception] could discern nothing, were it unceasingly attended by pleasure or by pain. Nevertheless our author, starting from so slight a warrant, applies his principle to perception universally.

When Anaxagoras says that larger animals have better powers of sense, and that sense perception varies in general with the size of the organs of sense, one of these propositions raises the question whether small animals or large animals have better powers of sense. For it would seem to be essential to keener sense perception that minute objects should not escape it. And we might reasonably suppose, too, that an animal with power to discern smaller objects could also discern the larger. Indeed it is held that, so far as certain of the senses are concerned, small animals are superior to large ones; and, in so far, consequently the perceptive power of the larger animals would be inferior. But on the other hand, if it appear that many objects actually do escape [the senses of] small animals, then the [sense perception of larger animals is superior. At the same time it were reasonable to suppose that what is true of the entire composition of the body will hold also of matters connected with sense perception. We may well doubt, then, as was said, the propriety of any such assertion. For in analogous cases things are not determined by size; but the most important factors seem to be the body's general state and its composition. In making the correspondence between [the senses and] their objects depend on size, Anaxagoras seems to be speaking after the manner of Empedocles, who explains sense perception by the supposition that [emanations] fit into the passages [of sense]. In the case of smell, however, there is a special difficulty: for he asserts that rarefied air is the more odorous; and yet that the animals which inhale the dense air have a keener sense of smell than those inhaling the subtile.

Anaxagoras' doctrine of the visual image is one some- what commonly held; for nearly everyone assumes that seeing is occasioned by the reflection in the eyes. They took no account of the fact, however, that the size of objects seen is incommensurate with the size of their reflection; and that it is impossible to have many contrasting objects reflected at the same time; and, farther, that motion, distance, and size are visual objects and yet produce no image. And with some animals nothing whatever is reflected,—for example, with those that have horny eyes, or that live in the water. More over according to this theory many lifeless things would possess the power of sight; for there is a reflection certainly in water, in bronze, and in many other things. His own statement is that colours are reflected in one another, but particularly the strong in the weak; consequently each of these—but especially black and the weaker colours generally—should possess the power of sight., For the reason just given, he holds that the organ of vision is of the same colour as the night, and that light is the cause of the visual reflection. But in the first place, we see light itself, without any image of it whatsoever; and in the second place, black objects and white objects alike lack light. And furthermore in other cases we are all the while seeing reflection arise in what is more brilliant and pure,—a fact entirely in keeping with his own statement that the membranes of the eyes are fine and lustrous. Now most [scientists] assume that the organ of vision itself is of fire, since colours partake of this element especially. And Anaxagoras himself, as I have said, upholds this rather common and hoary doctrine; IQ save that in the case of each and every sense he offers something original, and particularly of sight when he sets forth the part which size here plays in perception. But of the senses that have a more material character he offers no such clear account.

Clidemus alone spoke with originality in regard to vision; for the perceptive power of our eyes, he says, is due solely to their being transparent. We perceive with our ears because the air bursts in upon them and causes there a motion. With our nostrils we perceive in the act of inhaling the air, for there the air enters into some kind of combination. Savours and heat and cold are perceived by means of the tongue because it is spongy. With the rest of the body we perceive nothing other than the [qualities] named; and even of these qualities, there come to us from the body outside the special sense organs, only] warmth and moisture and their opposites. The ears, he maintains by way of exception, are of themselves incapable of passing judgment, but must ever report to the reason [what they receive]. Yet he does not, like Anaxagoras, regard reason as the source of all.

Diogenes connects the senses with the air, even as he connects with it both life and thought. He would accordingly seem to ascribe [perception] to likeness; for, he holds, there would be neither activity nor passivity unless all things were from a single [source]. Smelling is effected by the air about the brain; since the air is massed there III and is commensurate with odour; while the brain of itself, with its ducts," is already of light consistency. But [the cephalic air]" in some whose condition departs from this proper measure is too attenuated " and does not unite with the odours. Thus it is evident that perception occurs in anyone whose composition has this correspondence. Hearing arises when the air within the ears is set in motion by the external [air] and transmits [this motion] to the brain. Sight arises when objects are reflected in the pupil, but it " occasions perception only when mingled with the internal air. This is capable of proof: for if the ducts become inflamed, there is no union with the internal [air], and sight is impossible although the image is still there as before. Taste arises in the tongue because of its open and soft texture. As for touch, he offers no explanation either of its mode of action or of the objects with which it is concerned.

He then attempts to state upon what depends the greater acuteness of the senses, and in what kinds [of creatures] this is found. Smell, to begin with, is keenest in those who have least air in the head,—for then this air most readily unites [with the odours],—and in those, furthermore, who inhale through an unusually long, narrow [passage], for [odour] is thus more readily detected. Some animals in consequence are keener of smell than are men. Yet man's perceptive power is extremely acute whenever the odour corresponds to the [cephalic] air in point of com position.

Those have sharpest hearing whose ducts " are delicate and in whom the passage to the seat of sensation and of hearing is short, delicate, and straight, and in whom the external ear, furthermore, is erect and large; for the air in [the more external parts of] the ears, when set in motion, moves the air within. But if [the organs of hearing] be too wide and open, there is a ringing in the ears when the air is set in motion, and the sound [which we wish to hear] becomes inarticulate because it does not come upon [the internal air] at rest. Vision is keenest in such animals as have their [internal] air and their ducts refined—as is true of the other [senses],—and have an exceedingly lustrous eye. But since the eye reflects better a colour that stands in contrast with it, black-eyed " persons have a vision superior by day and for brilliant objects, while those with eyes of opposite hue see better by night. That the internal air, however, is the real agent of perception —being a tiny fragment of divinity—is proved by this, that when our minds are engrossed in other things we often neither see nor hear.

Pleasure and pain, he holds, arise in the following way. Whenever the air mingles in large quantities with the blood and sublimates it,—since the air is now in its normal state and pervades the entire body,—there is pleasure. But when [the condition is] abnormal and the air no longer unites with the blood, then the blood settles and becomes too sluggish and thick, and there is pain. In like manner [he explains] daring and health and their opposites. The tongue, he holds, is pre-eminently the judge of pleasure, for it is exceedingly soft and of open texture and all the ducts lead into it. Very many symptoms with the sick are consequently found here in the tongue. And in other animals [the tongue] reveals the colours [of their skin], for the variety and character [of these colours] are [there] reflected. Such is the manner and occasion, then, of perception's rise. Thinking, as was said, is due to pure dry air; for moisture clogs the intellect. Thought is at a low ebb consequently in sleep and in one's cups and in repletion. That moisture robs one of reason is proved by this, that the other living creatures are inferior of understanding, for they breathe air that comes from the earth and they take moister nourishment. It is true that birds breathe air that is pure, while yet their nature remains like that of fish; for the flesh [of birds] is firm and compact, and their breath is not allowed to penetrate the entire [body] but is checked in the region of the belly. As a result, it speedily digests the food, while [the animal] itself remains witless. But the character of their mouth and tongue aids and abets the food [in making them witless], for birds cannot understand one another. Plants are entirely bereft of thought because they are not hollow and consequently do not receive the air.

The same principle explains also why young children lack understanding; for they are excessively moist, and in consequence [the air] cannot make its way through out the body but is set apart in the breast, leaving them sluggish and witless. They are passionate and impetuous in general and flighty because the air in large quantities is excreted from their tiny bodies. This is the cause of forgetfulness also; for since the air does not penetrate the entire body, one cannot under stand. Which is proven by this: that when we try to remember, there is a feeling of oppression in the breast; but when [the missing thoughts is found, [the air] is dispelled ' and the weight of pain is lifted. In his effort to connect everything with the air, Diogenes fails at many points to produce conviction. For he makes neither sense perception nor thought a peculiar mark of things animate. For presumably such air and in such combination and correspondence can exist everywhere and in everything; if not, he ought to make this point explicit. Moreover [this condition might occur] in the different senses themselves, and consequently it would be possible for hearing to detect the objects of sight, and what we arrive at by smell some other creature should reach by some other [sense] because [this other sense] had a composition the same [as that of our sense of smell. And so, according to this theory, it would also be possible for us to detect odours by the breath taken into the chest, for [this air] might sometimes be proportionate to the odours.

His theory of vision, moreover,—that we see by means of the internal air,—is childish indeed. Yet in a measure he refutes those who regard the reflection [as the cause of sight], although he does not assign the [true] cause himself. Furthermore he attributes perception, pleasure, and thought to respiration and to the mingling [of air] with the blood. But many animals are either bloodless or do not breathe at all. And were it necessary for the breath to penetrate the entire body and not merely certain special parts,—for this is introduced merely for the sake of a small part [of the theory]—there would be nothing in this to prevent all [parts of the body]I from remembering and thinking. . . . But even if this were the case, it would offer no difficulty. For reason does not have its seat in all our members—in our legs and feet, for instance—but in determinate parts, even those by whose means, at the proper age, we exercise memory and the power of thought. Childlike, too, is his idea that men differ from animals— not in their essential nature, as animate things differ from inanimate,—but because they breathe purer air. For then one ought to show a difference of intelligence directly upon change of place, and high landers should be more intellectual than other men, and birds should surpass them all. For the character of the [birds'] flesh ' differs [from that of men and the higher animals] by no means so greatly as does the purity of the air [they breathe]. Moreover, [it is childish to hold] that plants lack the power of thought because they are not hollow, and that all those things that actually are hollow possess this power. Thus Diogenes, in his zeal to derive everything from his principle [the air], as we have indicated, strays repeatedly from the path of likelihood.

Democritus in his account of sense perception does not make it entirely clear whether it is due to contrast or to similarity. For in so far as he ascribes the action of the senses to an alteration, it would seem to depend on contrast; for the like is never altered by the like. On the other hand, sense perception would seem to depend on similarity in so far as he ascribes the perceptive process and, in a word, alteration to the fact that something is acted upon. For things that are not the same cannot be acted upon, he says; but even when things that are different do act, [their action is] not due to their difference but to the presence in them of something identical. Upon such matters as these he may consequently be understood either way. He now undertakes to discuss the [senses] each in turn. Vision he explains by the reflection [in the eye], of which he gives a unique account. For the reflection does not arise immediately in the pupil. On the contrary, the air between the eye and the object of sight is compressed by the object and the visual organ, and thus becomes imprinted; since there is always an effluence of some kind arising from everything. There upon this imprinted air, because it is solid and is of a hue contrasting [with the pupil], is reflected in the eyes, which are moist. A dense substance does not receive [this reflections but what is moist gives it admission. Moist eyes accordingly have a better power of vision than have hard eyes; provided their outer tunic be exceedingly fine and close-knit, and the inner [tissues] be to the last degree spongy and free from dense and stubborn flesh, and free too, from thick oily moisture; and provided, also, the ducts connected with the eyes be straight and dry that they may " perfectly conform " to the entering imprints. For each knows best its kindred.

Now in the first place this imprint upon the air is an absurdity. For the substance receiving such an imprint must have a certain consistence and not be ' fragile '; even as Democritus himself, in illustrating the character of the " impression ", says that " it is as if one were to take a mould in wax". In the second place, an object could make a better imprint upon water [than upon air], since water is denser. While the theory would require us to see more distinctly [an object in water], we actually see it less so. In general, why should Democritus assume this imprint, when in his discussion of forms ' he has supposed an emanation that conveys the object's form? For these images [due to emanation] would be reflected. But if such an imprint actually occurs and the air is moulded like wax that is squeezed and pressed, how does the reflection [in the eye] come into existence, and what is its character? For the imprint here as in other cases will evidently face the object seen. But since this is in so, it is impossible for a reflection facing us to arise unless this imprint is turned around. What would cause this reversal, and what the manner of its operation, ought, however, to be shown; for in no other way could vision come to pass. Moreover when several objects are seen in one and the same place, how can so many imprints be made upon the self-same air? And again, how could we possibly see each other? For the imprints would inevitably clash, since each of them would be facing [the person] from whom it sprung. All of which gives us pause.

Furthermore, why does not each person see himself? For the imprints [from ourselves] would be reflected in our own eyes quite as they are in the eyes of our companions, especially if these imprints directly face us and if the effect here is the same as with an echo, —since Democritus says that [in the case of the echo] the vocal sound is reflected back to him who utters it. Indeed the whole idea of imprints made on the air is extravagant. For we should be forced to believe, from what he says, that all bodies are producing imprints [in the air], and that great numbers of them are sending [their impressions] across one another's path,—a state of things at once embarrassing to sight and improbable on other grounds. If the impression moreover endures, we ought to see bodies that are out of sight and remote,—if not by night, at all events by day. And yet it would be but fair to assume that these imprints would persist at night, since then the air is so much cooler.

Possibly, however, the reflection in the eye is caused by the sun, in sending light in upon the visual sense in the form of rays,—as Democritus seems to mean. For the idea that the sun "drives the air from itself and, in thus repelling, condenses it", as he says,—this is in defensible; since the sun by its very nature disperses the air. He is unfortunate, too, in regarding visual perception as a function not only of the eyes but of the rest of the body as well; for he says that the eye must contain emptiness and moisture, in order that it may the more readily receive [impressions] and transmit [them] to the rest of the body. Farther, it is unreason able to declare that what is ' kindred ' to the organ of sight is preeminently the object of vision, and yet to explain the reflection [in the eye] by colour-contrast, on the ground that colours of the eyes' own hue are not reflected in them. And though he tries to explain how magnitudes and distances are reflected, he does not succeed. Thus Democritus in his endeavour to say something unique with regard to vision has bequeathed us the problem even farther from solution.

His explanation of hearing is very much like others'. For the air, he holds, bursts into the [aural] cavity and sets up a commotion. And while it gains entrance to the body in this same manner at every point, yet it enters more fully and freely through the ears because there it traverses the largest empty space, where least it " tarries ". In consequence no part of the body perceives [sounds] save this [sensory region]. But once the commotion has been started within, it is " sent broad cast " by reason of its velocity; for sound, he holds, arises as the air is being condensed and is making forcible entry [into the body]. So he explains sensation within the body, just as he explains perception external to it, by contact.

Hearing is keenest, he maintains, when the outer tunic is tough and the ducts are empty and unusually free from moisture and are well-bored in the rest of the body as well as in the head and ears; when, too, the bones are dense and the brain is well-tempered and that which surrounds it is exceedingly dry. For the sound thus enters compact, since it traverses a cavity large and dry and with good orifices, and swiftly the sound is "sent broadcast" impartially through the body and does not again escape.

Such hazy definition is found in other writers as well. Yet it is absurd, while original, to say that sound permeates the entire body, and that when it has entered by the organ of hearing it is spread to every nook and cranny, as though perception here were due not to the ears but to the body entire. For if [the rest of the body] is somehow affected conjointly with the organ of hearing, it by no means follows that the perception depends upon the [body as a whole]. For the [entire body] acts thus in the case of every sense; and not of the senses only, but of the soul as well.

Thus he accounts for sight and hearing. As for our other senses, his treatment hardly differs from that of the mass of writers.

Concerning thought, Democritus says merely that " it arises when the soul's composition is duly proportioned ". But if one becomes excessively hot or cold, he says, thinking is transformed; and it was for some such reason, the ancients well believed, that the mind became ' deranged '. Thus it is clear that he explains thought by the composition of the body,—a view perhaps not unreasonable in one who regards the soul itself as corporeal.

In sum and substance, then, these are the conclusions with regard to perception and thinking, which have come down to us from the earlier investigators.

[PART II. THE OBJECTS OF SENSE]
What may be the intrinsic character and quality of each of the senses' objects, the writers other [than Democritus and Plato] fail to state. Of the objects perceived by touch, they discuss the heavy and the light, the warm and the cold, saying that the rare and fine is hot; the dense and thick, cold,—which is the distinction Anaxagoras makes between air and aether. And in general [they explain] weight and lightness by the same [causes]—that is to say, by 'tendencies ' respectively upward and downward; and they further agree that sound is a movement of the air, and that odour is an emanation. Empedocles discusses the colours also, and holds that white is composed of fire, and black of water. The other investigators confine themselves to the statement that white and black are the fundamental colours and that the rest are derived from these by mixture. For even Anaxagoras treats of the [colours] in only a loose and general way.

Democritus and Plato, however, are the investigators who go into the question most fully, for they define the object of each sense; although [Plato] never robs these objects of their external reality, whereas Democritus reduces them one and all to effects in our sensuous faculty. Where the truth itself lies, is not the question we are now discussing. Let our aim be rather to report the range of each author's treatment and the precise definitions he gives, stating by way of preface his general method.

Democritus has no uniform account of all [the sensory objects]: some he distinguishes by the size [of their atoms], others by the shape, and a few by the [atomic] order and position. Plato, on the other hand, refers nearly all of them to effects in us, and to our perceptive faculty. Consequently each of these authors would seem to speak directly counter to his own postulate. For the one of them, who would have sensory objects to be but effects in our perceptive faculty, actually describes a reality resident in the objects themselves; while the other, who attributes the objects' character to their own intrinsic being, ends by ascribing it to the passive change of our perceptive faculty.

Heaviness and lightness, to begin with, Democritus distinguishes in terms of size. For if we were to divide each substance into its [atomic] units, then even though these were to differ in shape, he contends, their reality would have as its standard [of weight] their size. In the case of compounds, on the contrary, a substance that contains more of void is lighter; one that contains less is heavier. This at least is what he says in certain passages. In others, he holds that it is simply its fineness that makes a substance light.

And he speaks in almost the same terms of the hard and of the soft. For him anything is hard that is com pact; it is soft if loose; while the different degrees, and so on, [of such qualities are also explained] in accord with this idea. Yet the position and grouping of the void spaces that make substances hard or soft differ in some respects from those that make them heavy or light. Consequently though iron is harder than lead, lead is heavier. For iron is of uneven composition, and its void spaces are many and of large extent, although here and there iron is condensed; but speaking generally it contains more void spaces [than does lead]. But lead, though it has less of the void, is of even and uniform composition throughout; and so, while heavier than iron, lead is softer. Such is his account of the heavy, the light, the hard, and the soft.

As for the other sensory objects, he holds that none has an objective reality, but that one and all are effects in our sensuous faculty as it undergoes alteration,—and that from this faculty arises the inner presentation. For not even of heat or cold is there for him an objective reality; but configuration, in " undergoing a change ", effects a qualitative alteration in us also; since what is massed together in anything prevails in it, and what is widely diffused is imperceptible.

Proof that [these sensory qualities] are not objectively real is found in the fact that they do not appear the same to all creatures: what is sweet to us is bitter to others, and to still others it is sour or pungent or astringent; and similarly of the other [sensory qualities].

Moreover Democritus holds that " men vary in composition " according to their condition and age; whence it is evident that a man's physical state accounts for his inner presentation. So we must in general, according to him, hold this view regarding sensory objects. Nevertheless here too, as elsewhere, he falls back upon [atomic] figures; yet he does not recount the shapes [of the atoms] of all [the sensory objects], but centres his attention upon those of the tastes and of colours; and even of these, he describes with greater precision the [figures] connected with taste, although he refers the presentation itself to [the sentience of] man.

What is 'sour ', he holds, is at once ' angular ' in its [atomic] figure and is ' twisted ', minute, and thin. By its keenness it swiftly slips in and penetrates every where, and by its roughness and 'angularity' it draws the parts together and binds them. It also heats the body, in consequence, since it produces emptiness within; for whatever has most of empty space [amongst its atoms] is most heated.

' Sweet' consists of [atomic] figures that are rounded and not too small; wherefore it quite softens the body by its gentle action, and unhastening makes its way throughout. Yet it disturbs the other [savours], for it slips in among the other [atomic figures] and " leads them from their accustomed ways " and moistens them. And the [atomic figures] thus moistened and disturbed in their arrangement flow into the belly, which is most accessible, since empty space is there in greatest measure.

The 'astringent' taste, according to Democritus, is derived from [atomic] figures that are large and of many angles and are least rounded. For when these enter our bodies, they clog and occlude the ducts and prevent [their contents] from intermingling, and consequently stay the action of the bowels. ' Bitter ' is composed of small, smooth, round [atomic figures] whose surfaces moreover are furnished with hooks; as a consequence bitter is sticky and viscous. The taste derived from large [atoms] that are un rounded,—some of them are 'crooked', yet for the most part they are regular 's —this taste is ' saline '; [its atoms] therefore are not provided with ' many hooks '; (by ' crooked ' [atoms] he means such as overlap and become entangled in one another). [The saline quality is derived] from large [atoms] because salt comes to the surface of bodies; while if [its atoms] were small and were battered against the surrounding [particles], they would mingle with the whole; from unrounded [atoms], because what is saline is rough while the rounded is smooth; from [atoms] that are not ' crooked ', because these do not "stick to one another ", and in consequence they " crumble apart ".

The ' pungent ' savour according to him is small, round, and angular, but not irregular. Having many angles, this taste heats and melts by reason of its roughness, because it is small, round, and angular; for the angular too has this character. In a like manner he accounts for all the other effects of each [savour] by referring them to figures. But no one of all these figures is present, he holds, pure and without admixture of the others; on the contrary, there is a multitude of them in each savour, and the self same taste includes figures that are smooth, rough, round, sharp, and so on. The preponderant figure, however, exerts the most influence upon the faculty of sense and determines the [savour's] effect; and, more over, the condition in which it finds [us influences the result]. For it makes a great difference [what our condition is], inasmuch as the same substance at times causes opposite feeling, and opposite substances cause the same feeling. Such is Democritus's account of tastes.

In the first place, it might seem odd not to assign causes to all [sensory qualities] according to a uniform principle, but to explain heaviness and lightness, softness and hardness, by the fact that [the atoms] are large or small, and rare or dense, while heat and cold and the rest are explained by the figures [of the atoms]. In the second place, [it seems strange] to ascribe a resident and objective reality to the qualities heavy, light, hard, and soft (for the properties large and small, dense and rare are not relative to something other than [the substance itself]), and then to make heat, cold, and the rest entirely relative to sense, and this though he repeatedly says that the figure of heat is spherical. But the one glaring inconsistency running through the whole account is, that he no sooner declares [savours] to be subjective effects in sense than he distinguishes them by their figures; and he points out that the same substance appears bitter to some persons and sweet to others and has still a third quality for some other group. For the figure cannot possibly be a sub jective effect, nor can one- and the same figure be spherical for certain persons and of another shape for others (although such an assumption were perhaps in evitable if what is sweet for some is bitter for others), nor can the shapes [of atoms] change according to differences of state in us. And, in general, the [atomic] figure has an absolute existence, while sweetness and the sensuous object generally, as he says, is relative and existent in something beyond itself.

It is strange, furthermore, to insist that to all those who perceive the same things there comes the same subjective appearance, and to examine the true character of these things, when he has already said that to persons in different conditions there come different subjective appearances, and again that no one attains the truth of things better than does another. For it is probable that [in the attainment of truth] the better surpasses the worse, and the well the sick; since [the better and healthier are more in accord with the reality of things. l

But if there be no objective reality in sensory objects because they do not appear the same to all, there is manifestly none in animals or other bodies; for men disagree about these things, too. And yet even if the cause of sweet and bitter is not the same for us all, at least the bitterness l and sweetness appear the same for all. Democritus himself seems a witness to this; for how could that which is bitter for us be sweet or astringent for others, unless these very qualities had a definite nature? This he makes even more explicit in those passages where he says that the being of anything and the process by which it originated are real; and particularly when he says of bitter, that "[here we] have a portion of understanding." Upon such a showing, consequently, there would seem to be a general contradiction in his refusal to ascribe any objective reality to sensory objects. But there is, besides, the special contradiction indicated above, when he assigns a figure to the bitter, as he does to the other [savours], and yet says that [the bitter] has no objective reality. For either no [sensory object] has external reality, or else these tastes have such reality, since a common cause underlies them.

Moreover both heat and cold, which are supposed to be the primal source of things, probably have some objective reality; but if these, then the others also. He does, however, ascribe a certain substantive being to the qualities hard and soft, and heavy and light;— although in spite of this they seem to be counted [among the qualities] relative to us;—but he does not ascribe such substantive being to heat, and cold, and the rest. And yet, as he distinguishes the heavy and the light by the size [of their atoms], he ought to hold that all simple [bodies] have an impulse to move in the same direction; and consequently they would be of one and the same ' matter ' and would have a common nature. Yet upon such questions he seems to have followed those who make thought entirely a matter of change, a doctrine from hoary antiquity; since all the ancients, whether poets or sages, represented thought as dependent upon [bodily] disposition. But in assigning an [atomic] figure to each of the savours, Democritus has made this figure correspond to the effect which the savour produces in our feelings. The [figure therefore should be deduced], not from the [external savours] merely, but from our sense organs as well; above all, if these savours themselves are but subjective effects in these sense-organs. A spherical figure does not have the same ' power ' in every case, nor does any other figure; [a savour] must consequently be characterized with reference to the substrate affected, by stating whether it is composed of what is like or unlike [the substance of the sense organ], and how the change in the sensuous faculty comes to pass. And furthermore there should be offered an explanation applicable alike to all the sensory qualities that arise by touch, and not merely to those involved in taste., And yet these qualities [arising by touch] either show some difference when compared with savours—a difference which he should make clear—or else he has neglected to tell us what is the common explanation that here is possible.

The simple colours, he says, are four. What is smooth is white; since what neither is rough nor casts shadows nor is hard to penetrate,—all such substances are brilliant. But brilliant substances must also have open passages and be translucent. Now white substances that are hard have the structure just described,—for instance, the inner surface of cockle shells; for the sub stance here would be shadowless, ' gleaming ', and with straight passages. But the white substances that are loose and friable are composed of round particles, yet with these placed oblique to one another and oblique in their conjunction by pairs,' s while the arrangement as a whole is uniform in the extreme. With such a structure these substances are loose because [their particles are] in contact only over a small [portion of their surface]; friable, because their composition is so uniform; shadowless, because they are smooth and flat. But those substances are whiter, compared with one another, in which the figures are more exactly as described above and are freer from admixture with other figures and whose order and position more nearly conform to the given description. From such figures, then, is white derived.

Black is composed of figures the very opposite [to those of white],—figures rough, irregular, and differing from one another. For these cast shadows, and the passages amongst them are not straight nor easy to thread. Their effluences, too, are sluggish and con fused; for the character of the effluence also makes a difference in the inner presentation, as this emanation is changed by its retention of air.

Red is composed of figures such as enter into heat, save that those of red are larger. For if the aggregations be larger although the figures are the same, they produce the quality of redness rather [than of heat].' Evidence that redness is derived from such [figures] is found in the fact that we redden as we become heated, as do other things placed in the fire until they have a fiery colour. Those substances are redder that are composed of large figures—for example, the flame and coals of green wood [are redder] than those of dry. And iron, too, and other things placed in fire [become redder]. Those are most luminous, however, that contain the most fire and the subtilest, while those are redder that have coarser [fire] and less of it. Redder things, accordingly, are not so hot; for what is subtile is hot.

Green is composed of both the solid and the void,— the hue varying with the position and order of these constituents.

Such are the figures which the simple colours possess; and each of these colours is the purer the less the admixture of other figures. The other colours are derived from these by mixture.

Golden and copper-colour and all such tones, for in stance, come from white and red, their brilliance being derived from the white, their ruddiness from the red component; for in combination the red sinks into the empty spaces of the white. Now if green be added to white and red, there results the most beautiful colour; but the green component must be small, for any large admixture would not comport with the union of white with red. The tint will vary according to the amount [of green] that is introduced.

Crimson comes from white, black, and red,—the largest ' portion ' being red, that of black small, and of white midway; for thus it makes an appearance delightful to the sense. That black and red are present in it is patent to the eye: its brilliance and lustre testify to the presence of white; for white pro duces such effects.

Woad hue is composed of deep black and golden green, but with the major 'portion' black. Leek green is of crimson and woad, or of golden green and purplish. . . . For sulphur colour is of this character, with a dash of brilliance. Indigo is a mixture of woad and fiery red, with round figures and figures needle-shaped to give a gleam to the colour's dark ness.

Brown is derived from golden green and deep blue; but if more of the golden green be mixed, flame-colour is the result; for the blackness is expelled because [the golden green] is shadowless. And red, too, when mixed with white, gives almost a ' pure ' golden green, and not a black; which accounts for the fact that plants at first are of such a green before there is a heating and dispersion.

This completes the tale of colours he recounts; although he holds that the colours, like the savours, are endless in number according to their combinations,—according as we remove some and add others and ' combine ' them in varying proportion. For no one of these colours would be the same as another.

But first of all, his increase of the number of primaries presents a difficulty; for the other investigators propose white and black as the only simple colours. And in the second place, there is a difficulty when he fails to assign one and the same shape to all kinds of white, but attributes a different shape to the 'hard' whites from that which he ascribes to the whites of 'loose texture.' For it is improbable that [the whiteness] would have a different cause in substances differing merely in their tactile character. And, too, the cause of the difference [between white and black] would not lie in the figure [of the constituent particles], but in their position. For round figures, and indeed every kind of figure whatever, can cast shadows upon one another. And this is evident, for Democritus himself gives this reason for the smooth things that look black; for they appear thus, he holds, because they have the internal combination and arrangement characteristic of black. And again, [in giving his reason] for the white things that are rough; these are of large particles, he holds, and their junctions are not rounded off but are ' battlemented and the shapes of the figures are broken, like the earthworks in the approach to a city's wall. For such an arrangement, he says, throws no shadow, and brilliance is not hindered.

Moreover, how can he say that the whiteness of certain creatures becomes black if they be so placed that shadows are cast? He seems really to be talking about the nature of transparency and brilliance, rather than of whiteness. For to be easily seen through and to have passages that do not run zig-zag are features of transparency; but how many transparent substances are white? And further, to assume straight passages in substances that are white, and passages zig-zag in those that are black, implies that the very structure of the object enters [our sense organ]. Vision, he says, is due to an emanation and to the reflection in the organ of sight. But if this be so, what difference does it make whether the passages [in the object] lie end to end or zig-zag? Nor is it easy to believe that an emanation can by any possibility arise from the void. The cause of this, therefore, should be stated. For he seems to derive whiteness from light or something else; and accordingly offers the grossness of the air as also a reason why things seem dark.

His explanation of black, farther, is not easy to comprehend; for a shadow is (in his theory) some thing black, and at the same time it is an obscuration of what is white; white is therefore essentially prior [to black], Yet with this, he attributes [black] not only to shading but to the grossness of the air and of the entering emanation, as well as to disturbance of the eye. But whether these arise from mere opacity, or from some other source, and if so, what the character [of this farther source may be], he does not reveal.

It is singular, also, to assign no shape to green but to constitute it merely of the solid and the void. For these are present in all things, of whatsoever figures they are composed. He should have given some distinctive [figure] to green, as he has to the other colours. And if he holds [green] to be the opposite of red, as black is of white, it ought to have an opposite shape; but if in his view it is not the opposite, this itself would surprise us that he does not regard his first principles as opposites, for that is the universally accepted doctrine. Most of all, though, he should have determined with accuracy which colours are simple, and why some colours are compound and others not; for there is the gravest difficulty with regard to the first principles. Yet this would doubtless prove a difficult task. For if one could say, of tastes for example, which of them are simple, there would be more in what one said [than is found in Democritus upon them. As for smell, he says nothing definite except that something subtile emanating from heavy substances is the cause of odour. But what its character is, and by what this process is effected—which is perhaps the most important point of all,—on this we have never a word. There are some things of this kind, then, that Demo critus has neglected.

Plato holds o that a substance is hot which by the sharpness of its angles divides [the body]. But whenever, by reason of their fluidity, the larger particles expel the smaller, and—since they are unable to enter amongst them—yet encompass and compress them, this is cold. 'Shivering ' is our name for the conflict [between these particles]; while the affection is known as 'chill.' Hard is whatever the flesh yields to; soft, whatever yields to the flesh; and [the hard ness and softness of objects] relative to one another are explained in like fashion. Those particles yield that have a small base. Heavy and light should not be defined, he maintains, by resort to the relations ' up ' and 'down '; for these have no objective reality. But anything is light when it is with ease drawn to a place opposed to its own nature; it is heavy when this is done with difficulty. Of rough and smooth he has nothing to say, passing them by as of a character clear enough. With regard to pleasure and pain, he explains pleasure as a sudden and violent experience of return to the natural state; pain, as a sudden experience of forcible disturbance of the natural state; while the intermediate and imperceptible changes are explained in conformity with this. In the case of sight, accordingly, there is no pain or pleasure from the dissolution and recombining.

As for the savours, Plato when treating of water mentions four of its kinds; amongst the saps are wine, verjuice, oil, and honey. But in treating of the feelings produced in us, [he adds] an earthy savour. And as these coagulate and compact the organic juices, the rougher are astringent; the less rough, harsh. Those that rinse and purge the passages [of taste] are saline; such as are excessively detergent, even to the pitch of dissolution, are bitter? Substances that are filled with heat and are borne upward [in the head] and disintegrate [the very tissues] are pungent; those that cause a confusion are sharp; while those are sweet that, in company with the tongue's own moisture, relax or contract [the tissues] back to their natural state.

Odours, according to Plato, admit of no [true] classification, but are distinguished by their painful or pleasant [effect]. Odour is subtiler than water, though less refined than air; the proof is this, that if we inhale through an obstruction, the breath enters without odour. Thus odour is a kind of invisible vapour or mist from bodies; vapour being a transition from water to air, mist the transition from air to water. Sound, he holds, is a shock produced by the air—a shock through the ears to the brain and blood and penetrating to the soul. Tones are high and low, respectively, when swift and slow; they are in concord when the beginning of the slow tone is like the end of the swift.

Colour, for Plato, is a flame from bodies, a flame whose parts correspond to the organ of vision. What disintegrates [the organ] is white; what redintegrates it is black,—a contrast analogous to hot and cold in the case of the flesh, and to astringent and pungent in the case of the tongue. Fiery white is brilliant. . . . The rest of the colours are compounded of these. But as for the precise proportions, he says that one ought not to state them, even if one knew, since we have neither a necessary nor a probable account to give of them; or should one, upon experiment, find the event far otherwise, there need be no surprise; for God alone can bring such things to pass. This gives fairly well his thought and his mode of explanation.

Yet the following might well surprise one. First of all, he gives no uniform account of all [our sensory objects], not even of those that belong to the same class. For he describes heat in terms of figure, but he has not given a like account of cold. Then, if whatever is yielding is soft, evidently water and air and fire are soft. And since he says that any substance is yielding whose elements have a small base, fire would be the softest of all. But none of these statements is widely accepted, nor in general is it held that a thing is soft that moves freely around and behind [the entering body]; but only what yields in 'depth ', without [free] change of place.

Furthermore he does not define heaviness and lightness universally, but [only] in the case of things of earth; for it is held that, of these, a heavy object is one that is borne to an alien place with difficulty; a light one, with ease. But fire and air are held to be, and actually are, light by very tending toward their proper places. Hence it is not true that the body with more of kindred substance is heavy; and the one with less, light. For the more of fire we take, the lighter it is. Of Plato's two statements, then, both hold true if fire be placed on high; but neither holds of fire here on earth. And similarly in the case of earth; for from on high the greater mass would be borne hither more swiftly. Earth and fire therefore [for Plato are not universally heavy or light, but each is either, according to mere position. Nor would earth [have the same character here and there, s but quite the re verse; here the mass with less of kindred matter, there the mass with more, would be the lighter. All of which arises from Plato's defining heaviness and light ness, not as they are universally, but for the special case of things of earth.

Of the sapid substances, he fails to state what severally are their natures, even were we to suppose that their distinct varieties are precisely four; he merely sets forth the affections they occasion. For he says that the astringent or ' puckering ' taste contracts the passages, and that the saline taste cleanses them,—which is but an affection in ourselves. And the rest of the savours are treated after a like manner. But what we seek—since the affections themselves are clear as day—is rather the reality behind them and why they produce their results.

Regarding the objects of smell, too, one could well doubt whether there might not be differences of kind. For they differ in their affections, as well as in the pleasures they give us, quite as do the savours. Indeed [the two groups] would seem to be governed alike in all respects. As for smell itself, it is generally agreed that there is some emanation and that there is an inhalation of air. But it is incorrect to liken odour to vapour and mist, and to say that vapour and mist are identical. Nor does he himself seem actually so to regard them; for vapour is in transition from water to air, he says, while mist is in transition from air to water. And yet in regard to mist the very opposite is generally held to be the fact; for when mist arises water disappears.

Rather unsatisfactory, too, is the definition he gives of sound: for this definition is not applicable to all creatures impartially; and although he tries, he does not state the cause of the sensation. Moreover he seems to be defining, not sound itself, whether inarticulate or vocal, but the sensory process in us. As for the colours, he agrees in general with Empedocles, since his idea that particles are proportioned to the organ of sight " [amounts to the though] that certain elements fit into the passages [of sense]. It is absurd, however, to represent [in such a manner only this single one of our senses; as it is, also, to say without exception that colour is a flame. For while in some respects the colour white resembles flame, black would seem to be flame's opposite. And in depriving [of all rational necessity] the mixture which produces the other [colours], he has on the whole made it impossible to assign them to their causes, and has left [his case] in need of argument and warrant.