De Anima

That there is no other sense distinct from the five, by which I mean sight, hearing, smell, taste, touch, anyone may convince himself on the following grounds. Let us assume that, as a matter of fact, we have sensation of every sensible object for which touch is the appropriate sense, all qualities of the tangible, as such, being perceptible to us through touch. Let us further assume that, when any sense is lacking to us, an organ of sense must also be lacking; and further, that whatever we perceive by actual contact is perceptible by touch, a sense which we do possess, while whatever we perceive mediately and not by actual contact is perceptible by means of the elements, namely, air and water. And here are implied two cases. Suppose, first, we have perception by one and the same medium of two several things, different in kind from one another, then whoever possesses the appropriate sense-organ must be percipient of both: as, for example, if the sense-organ consists of air and air is also the medium of both sound and colour. Next suppose several media to transmit the same object, as both air and water transmit colour, both being transparent, then he who possesses one of these alone will perceive whatever is perceptible through both media. Now, of the elements, air and water are the only two of which sense-organs are composed. For the pupil of the eye is of water, and the ear is of air, and the organ of smell is of one or the other, while fire, if present anywhere, enters into all, since nothing can be sentient without warmth. Earth, again, belongs to none of the sense-organs, or, at most, is a constituent peculiar to touch. It follows, then, that outside water and air there is no sense-organ. Now sense-organs composed of air and water certain animals do, in fact, possess. We may infer, then, that all the senses are possessed by those animals which are fully developed and are not crippled: even the mole is found to have eyes beneath its skin. And thus, unless there exists some unknown body or some property different from any possessed by any of the bodies within our experience, there can be no sixth sense which we lack.

Nor, again, can there be any special sense-organ for the common sensibles, which we perceive incidentally by every sense; for example, motion, rest, figure, magnitude, number, unity. For all of these we perceive by motion. Thus it is by motion that we perceive magnitude, and consequently figure, figure being one variety of magnitude; while that which is at rest we perceive by the fact that it is not moved. Number we perceive by the negation of continuity and by the special sense-organs also: for each sensation has a single object. Clearly, then, it is impossible that there should be a special sense for any one of these; for example, motion: for in that case we should perceive them in the same way as we now perceive sweetness by sight (and this we do because we have a sense which perceives both, and by this we actually apprehend the two simultaneously when they occur in conjunction). Otherwise we should never have more than an incidental perception of them; as of Cleon's son we perceive not that he is Cleon's son, but that he is a white object, and the fact of his being Cleon's son is accessory to the whiteness. But of the common sensibles we have already a common perception, which is direct and not indirect, so that there cannot be a special sense for them. For, if there were, we should never perceive them otherwise than in the way in which we said we saw Cleon's son.

But the various senses incidentally perceive each other's proper objects, not as so many separate senses, but as forming a single sense, when there is concurrent perception relating to the same object; as, for instance, when we perceive that gall is bitter and yellow. For it is certainly not the part of any other sense to declare that both objects are one and the same. Hence you are sometimes deceived and, on observing something yellow, fancy it to be gall.

But, it might be asked, why have we several senses, instead of only one? I answer, it is in order that we may not be so likely to overlook the common attributes, such as motion, magnitude, number, which accompany the special sensibles. For, if sight had been our only sense and whiteness its object, we should have been more apt to overlook the common sensibles and to confuse all sensibles, because colour and magnitude, for instance, must always go together. As it is, the fact that the common attributes are found in the object of another sense also shows that they are severally distinct.

Inasmuch as we perceive that we see and hear, it must either be by sight or by some other sense that the percipient perceives that he sees. But, it may be urged, the same sense which perceives sight will also perceive the colour which is the object of sight. So that either there will be two senses to perceive the same thing or the one sense, sight, will perceive itself. Further, if the sense perceiving sight were really a distinct sense, either the series would go on to infinity or some one of the series of senses would perceive itself. Therefore it will be better to admit this of the first in the series. Here, however, there is a difficulty. Assuming that to perceive by sight is to see and that it is colour or that which possesses colour which is seen, it may be argued that, if you are to see that which sees, that which in the first instance sees, the primary visual organ, will actually have colour. Clearly, then, to perceive by sight does not always mean one and the same thing. For, even when we do not see, it is nevertheless by sight that we discern both darkness and light, though not in the same manner. Further, that which sees is in a manner coloured. For the sense-organ is in every case receptive of the sensible object without its matter. And this is why the sensations and images remain in the sense-organs even when the sensible objects are withdrawn.

Now the actuality of the sensible object is one and the same with that of the sense, though, taken in the abstract, sensible object and sense are not the same. I mean, for example, actual sound and actual hearing are the same: for it is possible to have hearing and yet not hear; again, that which is resonant is not always sounding. But when that which is capable of hearing operantly hears and that which is capable of sounding sounds, the actual hearing and the actual sound occur simultaneously, and we might, if we pleased, call them audition and resonance respectively. If, then, motion, action and passivity reside in that which is acted upon, then of necessity it is in the potentiality of hearing that there is actual sound and there is actual hearing. For the activity of agent and movent comes into play in the patient; and this is why that which causes motion need not itself be moved. The actuality of the resonant, then, is sound or resonance, and the actuality of that which can hear is hearing or audition, hearing and sound both having two meanings. The same account may be given of the other senses and their objects. For, just as acting and being acted upon are in the subject acted upon and not in the agent, so also the actuality of the sensible object and that of the sensitive faculty will be in the percipient subject. But in some cases both activities have a name; for example, resonance and audition: in other cases one or the other has no name. Thus, while the actuality of sight is called seeing, that of colour has no name; and, while the actuality of the taste-faculty is called tasting, that of the flavour has no name. Now, as the actuality of the object and that of the faculty of sense are one and the same, although taken in the abstract they are different, hearing and sound thus understood as operant must simultaneously cease to be or simultaneously continue in being, and so also with flavour and taste, and similarly with the other senses and their objects: but when they are understood as potentialities, there is no such necessity. On this point the earlier natural philosophers were in error, when they supposed that without seeing there was neither white nor black, and without tasting no flavour. Their statement is in one sense true, in another false. For the terms sensation and sensible thing are ambiguous. When they mean the actual sensation and the actual sensible thing, the statement holds good: when they mean potential sensation and potential sensible, this is not the case. But our predecessors used terms without distinguishing their various meanings.

If, then, concord consists in a species of vocal sound, and if vocal sound and hearing are in one aspect one and the same, [though in another aspect not the same], and if concord is a proportion, it follows that hearing must also be a species of proportion. And this is the reason why hearing is destroyed by either excess, whether of high pitch or of low. And similarly, in the case of flavours, excess destroys the taste, and in colours excessive brightness or darkness destroys the sight, and so with smell, whether the excessive odour be agreeable or pungent. All this implies that the sense is a proportion. Hence sensibles are, it is true, pleasurable when they are brought into the range of this proportion pure and unmixed; for example, the shrill, the sweet, the salt: in that case, I say, they are pleasurable. But, speaking generally, that in which ingredients are blended is pleasurable in a higher degree, accord more pleasurable to the ear than high pitch or low pitch alone¹, and to touch that which admits of being still further heated or cooled. The due proportion constitutes the sense, while objects in excess give pain or cause destruction.

Now each sense is concerned with its own sensible object, being resident in the organ, qua sense-organ, and judges the specific differences of its own sensible object. Thus sight pronounces upon white and black, taste upon sweet and bitter, and so with the rest. But, since we compare white and sweet and each of the sensibles with each, what in fact is it by means of which we perceive the difference between them? It must be by sense, for they are sensibles. And thus it is clear that the flesh is not the ultimate organ of sense; for, if it were, it would be necessary that that which judges should judge by contact with the sensible object. Nor indeed can we with separate organs judge that sweet is different from white, but both objects must be clearly presented to some single faculty. For, if we could, then the mere fact of my perceiving one thing and your perceiving another would make it clear that the two things were different. But the single faculty is required to pronounce them different, for sweet and white are pronounced to be different. It is one and the same faculty, then, which so pronounces. Hence, as it pronounces, so it also thinks and perceives. Clearly, then, it is not possible with separate organs to pronounce judgment upon things which are separate: nor yet at separate times, as the following considerations show. For, as it is one single faculty which pronounces that good and bad are different, so when it judges "A is different from B" it also judges "B is different from A" (and in this case the "when" is not accidental; I mean, accidental in the sense in which I may now say "Such and such things are different" without saying that they are different now. On the contrary, it pronounces now and pronounces that A and B are different now). That which judges judges, then, instantaneously and hence as an inseparable unit in an inseparable time. But, again, it is impossible for the same thing, in so far as indivisible and affected in indivisible time, to be moved at the same instant with contrary motions. For, if the object be sweet, it moves sense or thought in such and such a way, but what is bitter moves it in a contrary way, and what is white in a different way.

Is, then, that which judges instantaneous in its judgment and numerically undivided and inseparable, although separated logically? Then it is in a certain sense that which is divided which perceives divided objects; in another sense it is qua indivisible that the divided perceives them: that is to say, logically it is divisible, locally and numerically it is indivisible. Or is this impossible? For the same indivisible unity, though in potentiality each of two opposites, in the order of thought and being is not so, but in actual operation is divided: it is impossible that it should be at the same time both white and black, and hence impossible that it should receive at the same time the forms of white and black, if reception of the forms constitutes sensation and thought. Rather is the case parallel to that of the point, as some describe it, which is divisible in so far as it is regarded as one or two. Well then, in so far as the faculty which judges is indivisible, it is one and judges instantaneously; but, in so far as it is divisible, it is not one, for it uses the same point at the same time twice. So far as it treats the boundary-point as two, it passes judgment on two separate things with a faculty which in a manner is separated into two; so far as it treats the point as one, it passes judgment on one thing, and that instantaneously. So much, then, for the principle in virtue of which we call the animal capable of sensation.

There are two different characteristics by which the soul is principally defined; firstly, motion from place to place and, secondly, thinking and judging and perceiving. Both thought and intelligence are commonly regarded as a kind of perception, since the soul in both of these judges and recognises something existent. The ancients, at any rate, identify intelligence and perception: thus, in the words of Empedocles: "Wisdom of old for mankind is increased according to that which is present to them": and again "Whence they have also continually a shifting succession of thoughts." Homer's meaning, too, is the same when he says: "Such is the mind of men." In fact, all of them conceive thought to be corporeal like sensation and hold that we understand, as well as perceive, like by like: as we explained at the outset of the discussion. They ought, however, at the same time to have discussed error, a state which is peculiarly characteristic of animal life and in which the soul continues the greater part of its time. It follows from their premisses that either all presentations of the senses must be true, as some affirm, or contact with what is unlike must constitute error; this being the converse of the position that like is known by like. But, as the knowledge of contraries is one and the same, so, too, it would seem, is error with respect to contraries one and the same.

Now it is clear that perception and intelligence are not the same thing. For all animals share in the one, but only a few in the other. And when we come to thinking, which includes right thinking and wrong thinking, right thinking being intelligence, knowledge and true opinion, and wrong thinking the opposites of these, neither is this identical with perception. For perception of the objects of the special senses is always true and is found in all animals, while thinking may be false as well as true and is found in none which have not reason also. Imagination, in fact, is something different both from perception and from thought, and is never found by itself apart from perception, any more than is belief apart from imagination. Clearly thinking is not the same thing as believing. For the former is in our own power, whenever we please: for we can represent an object before our eyes, as do those who range things under mnemonic headings and picture them to themselves. But opining is not in our power, for the opinion that we hold must be either false or true. Moreover, when we are of opinion that something is terrible or alarming, we at once feel the corresponding emotion, and so, too, with what is reassuring. But when we are under the influence of imagination we are no more affected than if we saw in a picture the objects which inspire terror or confidence. There are also different forms even of belief; knowledge, opinion, intelligence and their opposites. But the difference between these species must be reserved for another discussion.

To turn to thought: since it is different from sense-perception and seems to include imagination on the one hand and conception on the other, we must determine the nature of imagination before we proceed to discuss conception. If, then, imagination is the faculty in virtue of which we say that an image presents itself to us, and if we exclude the metaphorical use of the term, it is some one of the faculties or habits in virtue of which we judge, and judge truly or falsely. Such faculties or habits are sensation, opinion, knowledge, intellect. It is clearly not sensation, for the following reasons. Sensation is either a faculty like sight or an activity like seeing. But we may have an image even when neither the one nor the other is present: for example, the images in dreams. Again, sensation is always present, but not so imagination. Besides, the identity of the two in actuality would involve the possibility that all the brutes have imagination. But this apparently is not the case; for example, the ant, the bee and the grub do not possess it. Moreover, sensations are always true, but imaginings prove for the most part false. Further, it is not when we direct our energies closely to the sensible object, that we say that this object appears to us to be a man, but rather when we do not distinctly perceive it [then the term true or false is applied]. And, as we said before, visions present themselves even if we have our eyes closed.

Neither, again, can imagination be ranked with the faculties, nor like knowledge or intellect, which always judge truly: it may also be false. It remains, then, to consider whether it be opinion, as opinion may be true or false. But opinion is attended by conviction, for it is impossible to hold opinions without being convinced of them: but no brute is ever convinced, though many have imagination. Further, every opinion implies conviction, conviction implies that we have been persuaded, and persuasion implies reason. Among brutes, however, though some have imagination, none have reason. It is evident, then, that imagination is neither opinion joined with sensation nor opinion through sensation, nor yet a complex of opinion and sensation, both on these grounds and because nothing else is the object of opinion but that which is the object of sensation: I mean, it is the complex of the opinion of white and the sensation of white, not surely of the opinion of good with the sensation of white, which alone could constitute imagination. To imagine, then, will be on this supposition to opine directly, not indirectly, that which we perceive. But there are false imaginings concerning things of which we hold at the same time a true conception. For example, the sun appears only a foot in diameter, but we are convinced that it is larger than the inhabited world: in this case, therefore, either, without any alteration in the thing and without any lapse of memory on our part or conversion by argument, we have abandoned the true opinion which we had about it; or else, if we still retain it, the same opinion must be both true and false. It could have proved false only in the event of the object having changed without our observing it. It is not, then, either one of the two, opinion and sensation, singly, or a combination of the two, which constitutes imagination.

Now when one thing is moved, something else can be moved by it. And imagination is thought to be a species of motion and not to arise apart from sensation, but only in sentient beings and with the objects of sense for its objects. Motion, again, may be produced by actual sensation, and such motion must resemble the sensation which caused it. From all this it follows that this particular motion cannot arise apart from sensation nor be found anywhere except in sentient beings: and in virtue of this motion it is possible for its possessor to do and experience many things: imagination, too, may be both true and false. The reasons for the last conclusion are as follows. Perception of the objects of the special senses is true, or subject to the minimum of error. Next comes the perception that they are attributes: and at this point error may come in. As to the whiteness of an object sense is never mistaken, but it may be mistaken as to whether the white object is this thing or something else. Thirdly, there is perception of the common attributes, that is, the concomitants of the things to which the special attributes belong: I mean, for example, motion and magnitude, which are attributes of sensibles. And it is concerning them that sense is most apt to be deceived. But the motion which is the result of actual sensation will be different according as it arises from one or other of these three kinds of perception. The first kind, so long as the sensation is present, is true: the other kinds may be false, whether the sensation is present or absent, and especially when the object perceived is a long way off. If then, imagination possesses no other characteristics than the aforesaid, and if it is what it has been described to be, imagination will be a motion generated by actual perception. And, since sight is the principal sense, imagination has derived even its name (φαντασία) from light (φάος), because without light one cannot see. Again, because imaginations remain in us and resemble the corresponding sensations, animals perform many actions under their influence; some, that is, the brutes, through not having intellect, and others, that is, men, because intellect is sometimes obscured by passion or disease or sleep. Let this account of the nature and cause of imagination suffice.

As to the part of the soul with which it knows and understands, whether such part be separable spatially, or not separable spatially, but only in thought, we have to consider what is its distinctive character and how thinking comes about. Now, if thinking is analogous to perceiving, it will consist in a being acted upon by the object of thought or in something else of this kind. This part of the soul, then, must be impassive, but receptive of the form and potentially like this form, though not identical with it: and, as the faculty of sense is to sensible objects, so must intellect be related to intelligible objects. The mind, then, since it thinks all things, must needs, in the words of Anaxagoras, be unmixed with any, if it is to rule, that is, to know. For by intruding its own form it hinders and obstructs that which is alien to it; hence it has no other nature than this, that it is a capacity. Thus, then, the part of the soul which we call intellect (and by intellect I mean that whereby the soul thinks and conceives) is nothing at all actually before it thinks. Hence, too, we cannot reasonably conceive it to be mixed with the body: for in that case it would acquire some particular quality, cold or heat, or would even have some organ, as the perceptive faculty has. But as a matter of fact it has none. Therefore it has been well said that the soul is a place of forms or ideas: except that this is not true of the whole soul, but only of the soul which can think, and again that the forms are there not in actuality, but potentially. But that the impassivity of sense is different from that of intellect is clear if we look at the sense-organs and at sense. The sense loses its power to perceive, if the sensible object has been too intense: thus it cannot hear sound after very loud noises, and after too powerful colours and odours it can neither see nor smell. But the intellect, when it has been thinking on an object of intense thought, is not less, but even more, able to think of inferior objects. For the perceptive faculty is not independent of body, whereas intellect is separable. But when the intellect has thus become everything in the sense in which one who actually is a scholar is said to be so (which happens so soon as he can exercise his power of himself), even then it is still in one sense but a capacity: not, however, a capacity in the same sense as before it learned or discovered. And, moreover, at this stage intellect is capable of thinking itself.

Now, since magnitude is not the same as the quiddity of magnitude, nor water the same as the quiddity of water (and so also of many other things, though not of all, the thing and its quiddity being in some cases the same), we judge the quiddity of flesh and flesh itself either with different instruments or with the same instrument in different relations. For flesh is never found apart from matter, but, like "snub-nosed," it is a particular form in a particular matter. It is, then, with the faculty of sense that we discriminate heat and cold and all those qualities of which flesh is a certain proportion. But it is with another faculty, either separate from sense, or related to it as the bent line when it is straightened out is related to its former self, that we discriminate the quiddity of flesh. Again, when we come to the abstractions of mathematics, the straight answers to the quality "snub-nosed," being never found apart from extension. But the straightness of that which is straight, always supposing that the straight is not the same as straightness, is something distinct: we may, for instance, assume the definition of straightness to be duality. It is, then, with another instrument or with the same instrument in another relation that we judge it. In general, therefore, to the separation of the things from their matter corresponds a difference in the operations of the intellect.

The question might arise: assuming that the mind is something simple and impassive and, in the words of Anaxagoras, has nothing in common with anything else, how will it think, if to think is to be acted upon? For it is in so far as two things have something in common that the one of them is supposed to act and the other to be acted upon. Again, can mind itself be its own object? For then either its other objects will have mind in them, if it is not through something else, but in itself, that mind is capable of being thought, and if to be so capable is everywhere specifically one and the same; or else the mind will have some ingredient in its composition which makes it, like the rest, an object of thought. Or shall we recall our old distinction between two meanings of the phrase "to be acted upon in virtue of a" "common element," and say that the mind is in a manner potentially all objects of thought, but is actually none of them until it thinks: potentially in the same sense as in a tablet which has nothing actually written upon it the writing exists potentially? This is exactly the case with the mind. Moreover, the mind itself is included among the objects which can be thought. For where the objects are immaterial that which thinks and that which is thought are identical. Speculative knowledge and its object are identical. (We must, however, enquire why we do not think always.) On the other hand, in things containing matter each of the objects of thought is present potentially. Consequently material objects will not have mind in them, for the mind is the power of becoming such objects without their matter; whereas the mind will have the attribute of being its own object.

But since, as in the whole of nature, to something which serves as matter for each kind (and this is potentially all the passive members of the kind) there corresponds something else which is the cause or agent because it makes them all, the two being related to one another as art to its material, of necessity these differences must be found also in the soul. And to the one intellect, which answers to this description because it becomes all things, corresponds the other because it makes all things, like a sort of definite quality such as light. For in a manner light, too, converts colours which are potential into actual colours. And it is this intellect which is separable and impassive and unmixed, being in its essential nature an activity. For that which acts is always superior to that which is acted upon, the cause or principle to the matter. Now actual knowledge is identical with the thing known, but potential knowledge is prior in time in the individual; and yet not universally prior in time. But this intellect has no intermittence in its thought. It is, however, only when separated that it is its true self, and this, its essential nature, alone is immortal and eternal. But we do not remember because this is impassive, while the intellect which can be affected is perishable and without this does not think at all.

The process of thinking indivisible wholes belongs to a sphere from which falsehood is excluded. But where both truth and falsehood are possible there is already some combining of notions into one. As, in the words of Empedocles, "where sprang into being the neckless heads of many creatures," then afterwards Love put them together, so these notions, first separate, are combined; as, for instance, the notions incommensurable and diagonal. And, if the thinking refers to the past or to the future, the notion of time is included in the combination. Falsehood, in fact, never arises except when notions are combined. For, even if white be asserted to be not-white, not-white is brought into a combination. We may equally well call every statement a disjunction. But at any rate under truth and falsehood we include not only the assertion that Cleon is white, but also the assertion that he was or will be. And the unifying principle is in every case the mind.

Since, however, the term indivisible has two meanings, according as a whole is not potentially divisible or is actually undivided, there is nothing to hinder us from thinking an indivisible whole, when we think of a length (that being actually undivided), or from thinking it in an indivisible time. For the time is a divisible or indivisible unit in the same way as the length thought of. We cannot therefore state what the mind thinks in each half of the time. For, if the whole be undivided, the half has only potential existence. But, if the mind thinks each half separately, it simultaneously divides the time also. And in that case it is as if the parts were separate lengths. If, however, the mind conceives the length as made up of the two halves, then the time may be regarded as made up of corresponding halves.

Again, that which is not quantitatively but specifically an indivisible whole the mind thinks in an indivisible unit of time and by an indivisible mental act. Per accidens, however, such specific unity is divisible, though not in the same way as they, the act of thought and the time required for the act, are divisible, but in the same way as they are whole and indivisible. For in these specific unities also there is present a something indivisible, though certainly not separately existent, the same as that which constitutes the unity of both the time and the length. And, as with time and length, so in like manner with whatever is continuous. But the point and every division and whatever is an undivided whole in the same sense as the point is clearly explained by the analogy of privation. And the same explanation holds in all other cases. How, for instance, is evil apprehended, or black? In some fashion by its contrary. But that which apprehends must potentially be, and must contain within itself, the contrary which it apprehends. If, however, there be something which has no contrary [some one of the causes], then it is itself the content of its own knowledge, is in actuality and is separately existent.

Now every proposition, like an affirmative proposition, predicating something of something, is true or false. But with thought this is not always so. When its object is the What in the sense of the quiddity and there is no predication, thought is in every case true. But, as the perception by sight of the proper object of sight is infallibly true, whereas in the question whether the white object is a man or not, perception by sight is not always true, so is it with immaterial objects.

Now actual knowledge is identical with the thing known. But potential knowledge is prior in time in the individual, and yet not universally prior even in time. For it is from something actually existent that all which comes into being is derived. And manifestly the sensible object simply brings the faculty of sense which was potential into active exercise: in this transition, in fact, the sense is not acted upon or qualitatively changed. Consequently this must be a different species of motion. For motion is, as we saw, an activity of that which is imperfect; but activity in the absolute sense, that is, activity of that which has reached perfection, is quite distinct.

Sensation, then, is analogous to simple assertion or simple apprehension by thought and, when the sensible thing is pleasant or painful, the pursuit or avoidance of it by the soul is a sort of affirmation or negation. In fact, to feel pleasure or pain is precisely to function with the sensitive mean, acting upon good or evil as such. It is in this that actual avoidance and actual appetition consist: nor is the appetitive faculty distinct from the faculty of avoidance, nor either from the sensitive faculty; though logically they are different.

But to the thinking soul images serve as present sensations: and when it affirms or denies good or evil, it avoids or pursues (this is why the soul never thinks without an image). To give an illustration: the air impresses a certain quality on the pupil of the eye, and this in turn upon something else, and so also with the organ of hearing, while the last thing to be impressed is one and is a single mean, though with a plurality of distinct aspects.

What that is by which the soul judges that sweet is different from warm has been explained above, but must be restated here. It is a unity, but one in the same sense as a boundary point, and its object, the unity by analogy of these two sensibles or their numerical unity, is related to each of the two in turn as they, taken separately, are to each other. For what difference does it make whether we ask how we judge the sensibles that do not fall under the same genus, or the contraries which do, like white and black? Suppose, then, that as A, the white, is to B, the black, so C is to D [that is, as those sensibles are to one another]. It follows, convertendo, that A is to C as B to D. If, then, C and D are attributes of a single subject, the relation between them, like that between A and B, will be that they are one and the same, though the aspects they present are distinct: and so, too, of their single subject. The same would hold, supposing A were the sweet and B the white.

Thus it is the forms which the faculty of thought thinks in mental images. And, as in the region of sense the objects of pursuit and avoidance have been defined for it, so also outside sensation, when engaged with images, it is moved to action: as, for instance, you perceive a beacon and say "That is fire"; and then [by the central sense], seeing it in motion, you recognise that it signals the approach of an enemy. But at other times under the influence of the images or thoughts in the soul you calculate as though you had the objects before your eyes and deliberate about the future in the light of the present. And when you pronounce, just as there in sensation you affirm the pleasant or the painful, here in thought you pursue or avoid: and so in action generally. And, further, what is unrelated to action, as truth and falsehood, is in the same class with the good and the evil. Yet in this, at any rate, they differ, that the former are absolute, the latter relative to some one concerned.

But the abstractions of mathematics, as they are called, the mind thinks as it might conceive the snub-nosed; qua snub-nosed, it would not be conceived apart from flesh, whereas qua hollow, if anyone ever had actually so conceived it, he would have conceived it without the flesh in which the hollowness resides. So, too, when we think of mathematical objects, we conceive them, though not in fact separate from matter, as though they were separate. And, speaking generally, mind in active operation is its objects [when it thinks them]. The question, whether it is possible for the mind to think anything which is unextended without being itself unextended, must for the present be postponed.

And now let us sum up what has been said concerning the soul by repeating that in a manner the soul is all existent things. For they are all either objects of sensation or objects of thought; and knowledge and sensation are in a manner identical with their respective objects. How this is so requires to be explained. Knowledge and sensation, then, are subdivided to correspond to the things. Potential knowledge and sensation answer to things which are potential, actual knowledge and sensation to things which are actual, while the sensitive and the cognitive faculties in the soul are potentially these objects; I mean, object of sensation and object of cognition respectively. It follows that the faculties must be identical, if not with the things themselves, then with their forms. The things themselves they are not, for it is not the stone which is in the soul, but the form of the stone. So that there is an analogy between the soul and the hand; for, as the hand is the instrument of instruments, so the intellect is the form of forms and sensation the form of sensibles. But, since, apart from sensible magnitudes there is nothing, as it would seem, independently existent, it is in the sensible forms that the intelligible forms exist, both the abstractions of mathematics, as they are called, and all the qualities and attributes of sensible things. And for this reason, as without sensation a man would not learn or understand anything, so at the very time when he is actually thinking he must have an image before him¹. For mental images are like present sensations, except that they are immaterial. Imagination, however, is distinct from affirmation and negation, for it needs a combination of notions to constitute truth or falsehood. But, it may be asked, how will the simplest notions differ in character from mental images? I reply that neither these nor the rest of our notions are images, but that they cannot dispense with images.

The soul in animals has been defined in virtue of two faculties, not only by its capacity to judge, which is the function of thought and perception, but also by the local movement which it imparts to the animal. Assuming the nature of sensation and intellect to have been so far determined, we have now to consider what it is in the soul which initiates motion: whether it is some one part of the soul, which is either locally separable or logically distinct, or whether it is the whole soul: and again, if a separate part, whether it is a special part distinct from those usually recognised and from those enumerated above, or whether it coincides with some one of these.

A question at once arises in what sense it is proper to speak of parts of the soul and how many there are. For in one sense there appear to be an infinite number of parts and not merely those which some distinguish, the reasoning, passionate and concupiscent parts, for which others substitute the rational and the irrational. For, if we examine the differences on which they base their divisions, we shall find that there are other parts separated by a greater distance than these; namely, the parts which we have just discussed, the nutritive, which belongs to plants as well as to all animals, and the sensitive, which cannot easily be classed either as rational or irrational. Imagination, again, is logically distinct from them all, while it is very difficult to say with which of the parts it is in fact identical or not identical, if we are to assume separate parts in the soul. Then besides these there is appetency, which would seem to be distinct both in concept and in capacity from all the foregoing. And surely it is absurd to split this up. For wish in the rational part corresponds to concupiscence and passion in the irrational. And, if we make a triple division of soul, there will be appetency in all three parts.

To come now to the question at present before us, what is it that imparts to the animal local movement? For as for the motion of growth and decay, which is found in all animals, it would seem that this must be originated by that part of soul which is found in all of them, the generative and nutritive part. Inspiration and expiration of breath, sleep and waking, subjects full of difficulty, call for subsequent enquiry. But to return to locomotion, we must enquire what it is that imparts to the animal progressive motion. That it is not the nutritive faculty is clear. For this motion is always directed to an end and is attended either by imagination or by appetency. No animal, which is not either seeking or avoiding something, moves except under compulsion. Moreover, if it were the nutritive faculty, plants also would be capable of locomotion and thus would have some part instrumental in producing this form of motion. Similarly it is not the sensitive faculty, since there are many animals which have sensation and yet are throughout their lives stationary and motionless. If, then, nature does nothing in vain and, except in mutilated and imperfect specimens, omits nothing that is indispensable, while the animals we are considering are fully developed and not mutilated—as is shown by the fact that they propagate their kind and have a period of maturity and a period of decline,—it follows that, if locomotion was implied in sensation, they would have had the parts instrumental to progression. Nor, again, is it the reasoning faculty or what is called intellect that is the cause of motion. For the speculative intellect thinks nothing that is practical and makes no assertion about what is to be avoided or pursued, whereas motion always implies that we are avoiding or pursuing something. But, even if the mind has something of the kind before it, it does not forthwith prompt avoidance or pursuit. For example, it often thinks of something alarming or pleasant without prompting to fear; the only effect is a beating of the heart or, when the thought is pleasant, some other bodily movement. Besides, even if the intellect issues the order and the understanding bids us avoid or pursue something, still we are not thereby moved to act: on the contrary, action is determined by desire; in the case, for instance, of the incontinent man. And generally we see that, although a man possesses a knowledge of medicine, it does not follow that he practises; and this implies that there is something else apart from the knowledge which determines action in accordance with the knowledge. Nor, again, is it solely appetency on which this motion depends. The continent, though they feel desire, that is appetite, do not act as their desires prompt, but on the contrary obey reason.

The motive causes are apparently, at any rate, these two, either appetency or intelligence, if we regard imagination as one species of thinking. For men often act contrary to knowledge in obedience to their imaginings, while in the other animals there is no process of thinking or reasoning, but solely imagination. Both these, then, are causes of locomotion, intelligence and appetency. By intelligence we mean that which calculates the means to an end, that is, the practical intellect, which differs from the speculative intellect by the end at which it aims. Appetency, too, is directed to some end in every case: for that which is the end of desire is the starting point of the practical intellect, and the last stage in this process of thought is the starting point of action. Hence there is good reason for the view that these two are the causes of motion, appetency and practical thought. For it is the object of appetency which causes motion; and the reason why thought causes motion is that the object of appetency is the starting point of thought. Again, when imagination moves to action, it does not move to action apart from appetency. Thus there is one single moving cause, the appetitive faculty. For, had there been two, intelligence and appetency, which moved to action, still they would have done so in virtue of some character common to both. But, as a matter of fact, intellect is not found to cause motion apart from appetency. For rational wish is appetency; and, when anyone is moved in accordance with reason, he is also moved according to rational wish. But appetency may move a man in opposition to reason, for concupiscence is a species of appetency. While, however, intellect is always right, appetency and imagination may be right or wrong. Hence it is invariably the object of appetency which causes motion, but this object may be either the good or the apparent good. Not all good, however, but practical good: where by practical good we mean something which may not be good under all circumstances.

It is evident, then, that motion is due to the faculty of the soul corresponding to this object,—I mean what is known as appetency. But those who divide the soul into parts, if they divide it according to its powers and separate these from one another, will find that such parts tend to become very numerous: nutritive, sensitive, intelligent, deliberative, with the further addition of an appetent part: for these differ more widely from one another than the concupiscent does from the passionate. Now desires arise which are contrary to one another, and this occurs whenever reason and the appetites are opposed, that is, in those animals which have a perception of time. For intelligence bids us resist because of the future, while appetite has regard only to the immediate present; for the pleasure of the moment appears absolutely pleasurable and absolutely good because we do not see the future. Therefore, while generically the moving cause will be one, namely, the faculty of appetency, as such, and ultimately the object of appetency (which, without being in motion itself, causes motion by the mere fact of being thought of or imagined), numerically there is a plurality of moving causes.

Now motion implies three things, first, that which causes motion, secondly, that whereby it causes motion, and again, thirdly, that which is moved; and of these that which causes motion is twofold, firstly, that which is itself unmoved and, secondly, that which both causes motion and is itself moved. The unmoved movent is the practical good, that which is moved and causes motion is the appetitive faculty (for the animal which is moved is moved in so far as it desires, and desire is a species of motion or activity) and, finally, the thing moved is the animal. But the instrument with which desire moves it, once reached, is a part of the body: hence it must be dealt with under the functions common to body and soul. For the present, it may be enough to say summarily that we find that which causes motion by means of organs at the point where beginning and end coincide; as, for instance, they do in the hinge-joint, for there the convex and the concave are respectively the end and the beginning, with the result that the latter is at rest, while the former moves, convex and concave being logically distinct, but locally inseparable. For all animals move by pushing and pulling, and accordingly there must be in them a fixed point, like the centre in a circle, and from this the motion must begin. Thus, then, in general terms, as already stated, the animal is capable of moving itself just in so far as it is appetitive: and it cannot be appetitive without imagination. Now imagination may be rational or it may be imagination of sense. Of the latter the other animals also have a share.

We must also consider what is the moving cause in those imperfect animals which have only the sense of touch. Is it possible that they should have imagination and desire, or is it not? It is evident that they feel pleasure and pain: and, if they have these, then of necessity they must also feel desire. But how can they have imagination? Shall we say that, as their movements are vague and indeterminate, so, though they have these faculties, they have them in a vague and indeterminate form? The imagination of sense, then, as we have said, is found in the other animals also, but deliberative imagination in those alone which have reason.— For the task of deciding whether to do this or that already implies reasoning. And the pursuit of the greater good necessarily implies some single standard of measurement. Hence we have the power of constructing a single image out of a number of images.—And the reason why the lower animals are thought not to have opinion is that they do not possess that form of imagination which comes from inference, while the latter implies the former. And so appetency does not imply the deliberative faculty. But sometimes it overpowers rational wish and moves to action; at other times the latter, rational wish, overpowers the former, appetency. Thus one appetency prevails over another appetency, like one sphere over another sphere, in the case where incontinence has supervened. But by nature the upper sphere always has the predominance and is a moving cause, so that the motion is actually the resultant of three orbits.

The cognitive faculty, however, is not subject to motion, but is at rest. The major premiss is universal, whether judgment or proposition, while the minor has to do with a particular fact: for, while the former asserts that such and such a person ought to do such and such an act, the latter asserts that a particular act is one of the sort and that I am such a person. Now it is the latter judgment which at once moves to action, not the universal. Or shall we say that it is both together, but the one is akin to the unmoved movent, the other is not?