V
PSYCHOLOGY
SOUL AND ITS FACULTIES
The object of psychology is ‘to discover the nature and essence of soul, and its attributes.’1 The method of dealing with the attributes is demonstration; is there, Aristotle asks, a corresponding method of discovering the essence? He suggests division as a possible method, and in effect adopts it. The first step is to determine to which of the main divisions of being—the categories -soul belongs, and again whether it is a potentiality or an actuality. But at this point a difficulty arises. Suppose that there are different parts of soul, and various species or perhaps even genera arising from the presence of these parts in various combinations; it may then be that there is no one definition of soul. It may be that the primary facts are the different kinds of soul, and that there is no one thing answering to the name ‘soul’ in general, or only a slight nucleus of common nature in the various souls.2
Aristotle’s answer is in effect that the kinds of soul are neither so much alike that any single definition of soul will give a sufficient idea of its varieties, ranging from its humble manifestations in plants and zoophytes to the heights it reaches in man or in God, nor yet so different that we cannot recognise a common nature in all its varieties. Geometrical figures may be arranged in an order beginning with the triangle and proceeding to more and more complex forms, each of which contains potentially all that precede. So too the forms of soul form a series with a definite order, such that each kind of soul presupposes all that come before it in this order, without being implied by them. The minimal soul is the nutritive; for this exists in all living or ‘besouled’ beings—in plants and animals alike. Next comes the sensitive soul, which exists in all animals. Within the sensitive soul the same scheme reappears, for touch is a minimal form of sensation presupposed by all the others, present whenever they are and sometimes when they are not.3 And it is perhaps not too fanciful to say that for Aristotle touch, taste, smell, hearing, sight form a series in which the distinctive nature of sensation, that of ‘receiving the form without the matter’ of its objects, is increasingly manifested.4
The sensitive soul has not merely the function of perceiving, but, as a necessary consequence of this, that of feeling pleasure and pain, and therefore of desiring, which is found in all animals. There are two other faculties which are outgrowths from the sensitive faculty, found in most animals but not in all. (1) There is an outgrowth from it on its cognitive side, which Aristotle calls imagination 
of this in turn memory is a further development. And (2) there is an outgrowth from it on its appetitive side, the faculty of movement.5 Finally there is a faculty peculiar to man, that of reason.6 This is treated as generically distinct from perception; yet to perception, when acting not in any of its specialised forms as sight, hearing, etc., but in its generic nature as perception, are assigned various functions which tend to bridge the gulf between sense and reason.
Aristotle tries to show the necessity of this order in the faculties of soul. The life of all living things, if it is to be maintained at all, must be maintained through the processes of growth and decay, and the nutritive function must be at work in all living things to preserve their existence. Sensation is not equally necessary; plants and motionless animals find their food automatically in the soil they grow from. But the power of movement presupposes sensation, since it would be useless without sensation; it is no use for an animal to move about unless it can recognise its food when it finds it. Further, touch is the most indispensable of the senses. It is not necessary that an animal should distinguish at a distance what is good and what is bad for it; but it is necessary that it should do so when actually in contact with the object; and further it is in virtue of its tangible qualities that food nourishes. Taste also, which is a modification of touch, is indispensable since it is the recognition of the qualities whereby food attracts and what is not food repels the animal.
The other senses are means not so much to being as to wellbeing. Perception at a distance, though not necessary, is a help to animals in getting their food and in avoiding what is bad for them. And further, hearing and sight in their various ways minister to the life of thought; hearing is of peculiar value because the use of speech is the main instrument of teaching and learning, and sight because it reveals with such precision differences between things not only in respect of its proper object, colour, but in respect of their number, size, shape, and movement.7
SOUL AND BODY
Aristotle raises early in the De Anima another question that takes us into the heart of his psychology. Are the attributes of soul, he asks, all common to its possessor, the unity of soul and body which we call a living being, or are some of them peculiar to soul?8 If soul has peculiar attributes, it will be separable from body. If not, it will only be thinkable apart from body by an act of abstraction akin to that by which we separate the mathematical attributes of bodies from their physical character. Most mental phenomena are attended by some bodily affection. And, anticipating a famous modern theory, he adds that where the requisite bodily conditions are present, emotions such as anger and fear are produced by the slightest mental cause or in the absence of any. Mental phenomena therefore are ‘formulae involving matter.’ The true definition of them will omit neither their form or end (their rational causation) nor their matter (their physiological conditions). Thus either soul, or at any rate this kind of soul, comes within the scope of the physicist. We should not define anger either as the dialecticians do, merely as desire of retaliation, or as the ordinary physicist does, merely as the boiling of the blood about the heart. The forms which are embodied in matter need a particular kind of matter for their embodiment, and it is as important to know this as it is to know the forms themselves.9
It will be seen that Aristotle is no holder of a two-substance doctrine. Soul and body are not two substances, but inseparable elements in a single substance. But the word ‘inseparable’ here needs careful consideration. Soul and body, like form and matter in general, are in a sense separable. The matter which is now linked with a soul to form a living thing existed before the union began and will exist after it ceases. It is only from form, not from this form, that this matter is inseparable. And again this form can exist apart from this matter. For in Aristotle’s view it is one form that is embodied in all the members of a species, and it can exist independently of any one member though not of all. It requires for its existence, therefore, not this matter but this kind of matter. It requires a body with a certain kind of chemical constitution and a certain shape, and it cannot exist embodied in another kind of body. To speak of transmigration of human souls into animal bodies is like supposing that carpentry could embody itself in flutes instead of in chisels.10 Nor can soul exist disembodied -though here Aristotle makes a reservation in favour of the highest element in the human soul, the active reason, which, as it ‘comes in from outside,’11 exists too after the body’s death,12 though whether in an individual form or merged in some wider spiritual unity, Aristotle does not say.
From this general theory of the relation of soul and body, it follows that Aristotle had not conceived the notion of the self as a pure spiritual being to which its body is as much part of the outside world as other physical things. Rather, for him, soul and body form a union which while it lasts is complete, and in which soul and body are merely aspects distinguishable by the philosophic eye. A notion like that of Descartes, that the existence of the soul is the first certainty and the existence of matter a later inference, would have struck Aristotle as absurd. The whole self, soul and body alike, is something given and not questioned. But so too is the physical world. Aristotle sometimes uses language suggestive of idealism, but in the main he might perhaps be called a naïve realist. The language which suggests idealism is that in which he represents thought as identical with its object.13 But the underlying view is not that the object is constituted by thought, but that the mind is a ‘place of forms’ or ‘form of forms,’14 a thing which until it apprehends some universal is a mere potentiality, and which when it does apprehend a universal is entirely characterised by the apprehension, so that it may be said to have become one with its object. This is not idealism but extreme realism, allowing for no modification, still less construction, of the object by mind.
There are three marks of soul which Aristotle finds to have been recognised by his predecessors. He accepts all three characteristics, but rejects earlier theories with regard to them. Soul is a cause of movement but not self-moving; it moves without being moved. It knows, but it must not for that reason be thought to be composed of the same elements as that which it knows. It is incorporeal, and the earlier theories do not conceive its incorporeality distinctly enough.
At least one other important point emerges in the criticism of earlier thought which occupies Book 1 of the De Anima. Is the whole soul, Aristotle asks, involved in each of its activities, or should these be assigned to different parts?15 Should life be assigned to one or more of these parts, or has it a distinct cause? If the soul is divisible, what holds it together? Not the body (which rather is held together by the soul). What holds soul together must have the best title to the name ‘soul.’ If this has unity, why not ascribe unity to the soul itself at the outset; if it is divisible, what holds it together? Again, does each part of the soul hold together some part of the body? Plants and some insects, after division, have all the parts of their soul in each of the separated parts of their body. Thus the fission of which the soul admits is not into qualitatively different parts, but into parts each of which has the quality of the whole. Soul in fact, though Aristotle does not put it so, is homoeomerous, like a tissue, not an organ. And though he often uses the traditional expression ‘parts of the soul’, the word he prefers is ‘faculties.’ His is a faculty psychology, but not in the sense that he evades the task of the genuine explanation of facts by referring to a mystical faculty of doing this or doing that. He is simply taking account of the fact that the soul does exhibit a variety of operations, and that behind each of these intermittent operations we must suppose a permanent power of so operating. But these faculties do not coexist like stones in a heap. They have a definite order, an order of worth and a reverse order of development in the individual. Further, they have a characteristic which we may roughly call interpenetration. Thus for instance intellect and desire are distinct faculties, but the highest species of desire is of a kind which can only occur in beings which have intellect, and is itself intellectual.16 Choice or will may equally well be called desiring reason and reasoning desire, and in it the whole man is involved.17
In the second book Aristotle begins the positive exposition of his own theory. He first defines soul. It is clear to what category it belongs. For bodies, above all things, are universally held to be substances; and among bodies, above all others natural bodies, for these are the origin of all others, inasmuch as artificial bodies are made out of them. Now among natural bodies are included not only the elements and their inanimate compounds but also animate bodies. And animate bodies are substances not in the secondary sense in which matter (or potentiality) and form (or actuality), which are really elements in substance, may be called substance; they are individual independent substances concrete of matter and form. In this concrete unity it is evident that body plays the part of matter or possessor of attributes, and soul that of form or essential attribute. Aristotle is helped here by the fact that the natural expression in Greek for a living thing is
‘besouled body,’ where ‘besouled’ evidently stands for the attribute that distinguishes living from other bodies, the power (at the least) of self-nourishment, with or without the powers that mark off the higher living things from the lower. Soul is, then, the form or actuality of a living thing. But ‘actuality’ is ambiguous. As compared with a layman, a man of science has the actuality of knowledge even when he is not thinking scientifically; but he has it in a fuller sense when he is so thinking. Similarly soul is the first actuality of a living body, while its exercise of function is its second or fuller actuality. A man is besouled even when he is asleep, but he is not then fully actual; his functions, except his vegetative function, are then dormant. Now a living body is just a body endowed with organs, i.e. containing a diversity of parts cunningly adapted to different activities. Soul is thus ‘the first actuality of a natural body furnished with organs.’ In the living thing we distinguish the body which is matter and the soul which is form, just as in an axe we distinguish its material and its axeness, or in the eye the pupil and the power of sight; and we distinguish the first actuality, the soul, from the second actuality, the waking life, as we distinguish axeness from actual cutting and the power of sight from actual seeing. Obviously, then, soul is inseparable from body, unless there be some part of soul— Aristotle is thinking of reason—which is not the actuality of any body.18But we are left with the question how, if soul is such an actuality, any part of it can fail to be such; the connexion of reason with the other faculties is one of the obscurest parts of his psychology.
A definition so abstract as this will not help us much to understand the varied phenomena of soul, and Aristotle, aware of this, proceeds to give a more concrete account, one which specifies in the way indicated above the main faculties involved in soul. He then goes on to treat of these in detail, and first of nutrition.
NUTRITION
It is a mistake, he points out, to ascribe the growth of living things to the mere action of the elements contained in them.19 Even fire or heat is but an auxiliary cause of nutrition. In all natural wholes there is ‘a limit and a ratio of growth and size’— a limit of size proper to an animal of any given species, a ratio to be observed between the parts of its body; and this limit and ratio belong to the side of form not of matter, of soul not of body. The truth is, not that fire or heat is the cause of growth, but that soul acts on the hot substance in the body,20 which in turn produces qualitative change in the food, just as the steersman moves his hand, which in turn moves the rudder and thereby steers the ship. The soul is an unmoved mover, the hot substance moves by being moved, the food is merely moved (i.e. chemically changed).
It had been disputed whether nourishment is effected ‘by what is like’ or ‘by what is unlike.’ Aristotle solves the question by pointing out that nutrition is assimilation, the making like of what was unlike.
The ultimate aim of nutrition is the preservation not of the individual life, which is in any case doomed to speedy extinction, but of the species, whereby alone living things can ‘share in the eternal and the divine,’ Reproduction is ascribed by Aristotle to the same faculty as nutrition; and the full name of the primary or minimal faculty of soul is ‘the faculty of nutrition and reproduction.’
SENSATION
Sensation had been treated by most of Aristotle’s predecessors as if it were essentially a passive process in which the sense-organs are qualitatively changed by the object. In opposition to this view he insists21 that if sensation is to be called an alteration, a distinction must be drawn between two kinds of alteration. Sensation is not an alteration of the kind which is simply the replacement of a state by its opposite, but of that which is the realisation of potentiality, the advance of something ‘towards itself and towards actuality,’22 or in the language of the Physics23 a perfecting. The distinction is sound but does not take us far enough. The building of a wall is also a perfecting,24 and the distinction between the two kinds of alteration, while it brings out the fact that the act of sensation is that for which the sense-organ and the faculty of sensation all along existed, does not bring out the distinctively mental, non-corporeal nature of the act. This is better brought out in another passage25 in which Aristotle emphasises the complete difference between the physical modification of plants or inanimate things by sensible qualities, and the mental fact of sensation produced in animals by these same qualities. And it is still better brought out in the description26 of sensation as a discriminative power from which the highest acts of cognition are reached by a continuous development,
But Aristotle cannot be said to hold successfully to the notion of sensation as a purely mental activity having nothing in common with anything physical. He is still under the influence of earlier materialism. One set of thinkers had described perception as perception of like by like, another as perception of unlike by unlike. Both views agreed in supposing perception to be a modification of the body of the percipient by an external body. Aristotle solves the question, as he has solved the similar question about nutrition, by describing the process as one in which things unlike become like, the sense organ is assimilated to the object. The hand becomes hot, the eye coloured,27 and—he would add—the tongue becomes flavoured, the nose odorous, the ear resonant. Perception is distinguished from nutrition by the fact that while in the latter the matter of the food is absorbed, the former is receptive of form without matter.28 Now, if this assimilation of the organ to the object takes place, it does nothing to explain the essential fact about perception, that on this physical change supervenes something quite different, the apprehension by the mind of some quality of an object. It is only if reception of form means awareness of form that it is a true description of perception; and the description of the organ as becoming qualified by the form of its object is irrelevant. The phrase ‘receptive of form’ covers a radical ambiguity.
There is thus a certain amount of confusion between psychology and physiology in Aristotle’s account of perception. To pursue his physiology into somewhat greater detail, his view is as follows. Each sense-organ is sensitive to one or more sets of qualities ranging between extremes; e.g. the eye is sensitive to colour, which for Aristotle forms a series in which each intermediate consists of white and black combined in a certain ratio. To be sensitive to the whole range of these qualities, the organ must itself be characterised by a mixture of them in which neither extreme too much preponderates. The sense is thus a mean or ratio. In order that the organ may be affected by an external object, three conditions must be satisfied. (1) The change set up by the object in the medium must have a certain intensity; otherwise the inertia of the organ will prevent it from being affected. This is why very small coloured objects or very slight sounds cannot be perceived separately, although when they form parts of larger objects or louder sounds they are perceived potentially in the sense that they can be recognised by thought as constituents involved in the perceived object, And (2) the ratio in which the contraries are combined in the object must be to some extent different from the ratio of their combination in the organ. Thus the hand does not perceive as hot or cold what has the same temperature as itself. But (3) the difference between the ratios must not be too great. A certain variation in the ratio of the contrary qualities is compatible with the continued existence of the organ, but if the ratio is too greatly disturbed the organ is destroyed.29 And since touch is the indispensable sense, an excess of certain of the tangible qualities—heat, cold, or hardness30 -will in destroying the organ destroy the animal as well.31
The actualisation of perception is at the same time the actualisation of the object. Actual sound and actual hearing are merely distinguishable aspects of a single event. Apart from actual hearing there is not actual but only potential sound. At the same time, Aristotle opposes the earlier view that, without seeing there is neither white nor black.’32 His meaning must be that over and above their primary qualities objects have in the absence of percipients a definite qualification in virtue of which they produce sensations when percipients are present, But into the difficulties presented by these ‘permanent possibilities of sensation’ he does not enter.
Aristotle divides the objects of perception into three classes.33 Two of these are perceived directly—the sensibles peculiar to each sense and those which are common to all,34 or at least to sight and touch.35 About the former, deception is impossible or at all events infrequent. The full list of the common sensibles recognised by Aristotle is—movement and rest, number and unity, shape, size, and (we should probably add) time.36 The third kind of object of perception is that which is perceived incidentally as a concomitant of a ‘special sensible’; if you see a white object which is the son of Diares, you incidentally perceive the son of Diares.
There is much that is of not merely historical interest in Aristotle’s treatment of the special senses and their objects.37 A topic to which much attention is directed is the constitution of the organ and of the medium—and he holds that even touch employs a medium (the flesh), the organ of touch being not the flesh but ‘something within.’38 With regard to sight, he builds his theory39 on the observed facts (1) that an object placed upon the eye is not seen (which shows that a medium is necessary), and (2) that whereas fire can be seen either in light or in darkness, non-luminous coloured objects can only be seen in light.40 He supposes therefore that fire (as well as the heavenly bodies) has a power which non-luminous objects have not; that of ‘making actually transparent the potentially transparent.’ Potential transparency is a character common to air, water, and many solids. The state of actual transparency in such a body is light. Light is thus not a movement but an actuality or state; and it is produced not by a movement but by an instantaneous qualitative change effected in some potentially transparent medium. This is the first stage. The second is that in which a potentially coloured body acts upon, i.e. produces a further qualitative change in, the now actually transparent medium, and thus becomes actually coloured and produces actual sight. Alexander of Aphrodisias, recognising the two stages involved in Aristotle’s theory—the production of light and the production of colour—goes as far as to call colour ‘a sort of second light’ Fire and the heavenly bodies are the only things which can produce the first change in the medium as well as the second; they can be seen ‘in the dark’ just because they first make the dark light.
So far the transparent has figured only as external medium, but in the De Sensu41 its significance is extended in two ways. (1) Aristotle notes as a result of certain observations that the real organ of sight is not the outer surface of the eye but something within the head. A transparent medium must therefore extend right up to the inner organ, and hence the crystalline lens has to be composed of a transparent substance, water. And (2) transparency is now treated as being present in greater or less degree in all bodies whatsoever, and colour is described as the boundary of the transparent in bodies (i.e. in so far as the transparent is imprisoned in bodies mainly opaque), while light is the actuality of the transparent in its unbounded condition, i.e. as it exists in transparent media such as air and water.
SENSUS COMMUNIS
Aristotle’s account of the special senses, though it contains much acute reasoning, is largely vitiated by being bound up with an untenable physics and physiology. We must turn to his account of unspecialised perception, sensus communis. The phrase is rare in Aristotle,42 but conveniently sums up a whole mass of doctrine, provided it be interpreted not as being another sense over and above the five and apprehending a more varied group of objects, but as the common nature inherent in all the five. We must think of sense as a single faculty which discharges certain functions in virtue of its generic nature but for certain purposes specifies itself into the five senses and creates for itself organs adapted to their special functions.
The functions in which the perceptive faculty operates in this unspecialised way are the following:—(1) The perception of the ‘common sensibles.’43 All of these are’ Aristotle maintains, perceived by means of movement, i.e. a mental movement which he regards (rather obscurely) as proportioned to the object. The common sensibles are incidental to the special sensibles44 just as much as are the objects which are technically called the ‘incidentals,’ but he distinguishes between the two on the ground that whereas the coincidence, say, of white with sweet or with the son of Diares is a merely occasional one, every object—at least of sight and touch—has size, shape, duration, either rest or movement, either unity or number. We perceive the common sensibles by sight not qua sight, but in virtue of the general perceptive faculty which besides its specialised functions of sight, hearing, etc., has an unspecialised function relative to the qualities common to all sensible objects.
(2) The perception of the ‘incidental sensibles.’ This is first illustrated by the perception that the white object seen is the son of Diares.45 But later46 a distinction is drawn. There is (a) such perception as that of the sweet by sight when the two qualities occur together (i.e. in an object which we have previously seen and tasted but are now only seeing), and (b) such perception as that of the son of Cleon by sight. In both cases modern psychology holds that memory and association are involved as well as perception; the cases differ in regard to the complexity of what is called up by association on the stimulus of the present perception. In ascribing the apprehension of the incidentals and of the common sensibles to perception without definitely recognising the part played by association, Aristotle leaves unexplained (though he notes its existence) the fallibility of such perception as compared with that of the special sensibles.
(3) The perception that we perceive.47 Is it by sight, Aristotle asks, that we perceive that we see, or by some other sense? (a) If by some other, then (i) since that which perceives sight must perceive the colour which is the object of sight, there will be two senses which perceive colour, and (ii) we must either suppose a third sense by which we perceive that we perceive that we see, and so ad infinitum, or come ultimately to a sense which perceives itself; and if the latter, we might as well have ascribed self-consciousness to the original sense of sight. (b) On the other hand if we do this, then since to perceive by sight is to see, and what is seen is colour or the coloured, that which originally sees will have to be coloured. To this difficulty Aristotle replies that (i) ‘to perceive by sight’ is a wider expression than ‘to see’; we perceive darkness by sight though we do not see it; and (ii) that which sees is in a sense coloured, since the sense-organ receives the sensible object without its matter, i.e. becomes qualified by the same quality, and thus it is that perceptions and imaginations remain in the sense-organs when the objects have gone.
Aristotle’s answer is in effect that it is by sight we perceive that we see, but by sight not qua sight but qua perception. This is one of the earliest passages of any author in which the difficulties involved in self-consciousness are discussed.48 Aristotle does not assign all self-consciousness to a single central faculty. Knowledge, perception, opinion, and reasoning, while primarily engaged with obsjects other than themselves, each in passing apprehends itself. But elsewhere this reflexive activity is described as that which makes life valuable,49 and the divine life is depicted as pure self-knowledge, ‘knowing of knowing,’50
(4) Discrimination between the objects of two senses.51 This, Aristotle argues, cannot be effected by one sense alone, nor by both acting separately. It must be the work of a single faculty, operating in a single moment,—a synthetic unity of apperception, as it was later to be called. Aristotle suggests that the synthesis is the work of a faculty which is one in place and number, but contains differences of aspect or operation. But, he points out, while one thing may be potentially black and white, it cannot be actually both at once, and similarly a single sense or organ cannot be qualified by whiteness and sweetness at once, which is a necessary precondition of its discriminating them. And he can only meet the objection by the analogy of the point, which is at once actually the beginning of one line and the end of another.
Elsewhere52 he goes further and argues that the simultaneous perception of two qualities, whether of the same genus (white, black) or of different genera (white, sweet), involves the operation of the sensus communis.
(5) Aristotle argues that the inactivity of all the senses which is found in sleep cannot be a mere coincidence but must be due to the inactivity of the central perceptive faculty of which they are differentiations53—an inactivity for which he attempts to give physiological reasons54 as well as a final cause.55
IMAGINATION
We now come to a faculty which is in Aristotle’s view a sort of by-product of sensation, viz. ‘imagination.’56
is in its original meaning closely related to 
‘to appear,’ and stands for either the appearance of an object or the mental act which is to appearing as hearing is to sounding. To this usage belong the passages in which Aristotle speaks of 
as being at work in the presence of the sensible object, as when he distinguishes it from opinion by pointing out that while the sun appears to be only a foot across we believe it to be larger than the inhabited world.57 This apparently amounts to assigning to 
the work, formerly assigned to sensation, of perceiving the common sensibles. And this interpretation is confirmed by a passage58 in which he distinguishes between
with respect to the special sensibles, the incidentals and the common sensibles, and points out that while in the first 
case is infallible so long as the sensation is present, in the other two it is fallible even in the presence of the sensation. This amounts to throwing on to
the work of apprehending the incidentals and even the special sensibles as well as the common sensibles; and sensation would accordingly be reduced to the level of a mere passive affection which has to be interpreted by 
before it can give any information or misinformation about objects.
But for the most part Aristotle describes imagination in a way which involves no such reversal of his doctrine of sensation; and it may be doubted whether the passages just referred to represent his deliberate view. Usually 
is described as operating only after the sensible object has gone. The ‘movement of the soul through the body’ which perception is sets up a repercussion both in the body and in the soul— though as regards the soul the effect, until recollection takes place, is potential, i.e. not a conscious state of mind but an unconscious modification of the mind. At some later time, owing for instance to the suppression of sensation in sleep, the movement becomes actual; i.e., an image similar to but less lively than the sensation, and less trustworthy as a guide to objective fact, is formed and attended to; and this is the act of imagination. The physiological condition of this is that the repercussion in the sense-organ has to be transmitted, with the blood, by the ‘connate spirit’ to the central sense-organ, the 59
The main functions of
apart from the interpreting of present sensation, are: (1) The formation of after-images, of which Aristotle notes both the positive and the negative kind.60
(2) Memory. Aristotle begins61 by emphasising the reference of memory to the past, and infers that it is a function of the faculty by which we perceive time, i.e. of the ‘primary faculty of perception,’ the sensus communis. Memory, he adds, is impossible without an image. It is therefore a function of that part of the soul to which imagination belongs. But it is not the present image but the past event that is remembered; how can this be? Aristotle’s answer is that what is produced in the soul by perception is a sort of picture or impression of the percept, like the impression of a signet ring. Now in seeing a picture we may be said to become aware of its original; and similarly it is possible, in being aware of an image, to be aware of it as the image of something, and of something past. When these two conditions are fulfilled we have not mere imagination but the more complex act called memory. So much akin are the two operations, he points out, that it is possible to have a memory-image and yet suppose it to be a mere image, or to have a mere image and suppose it to be a memory-image.
From memory Aristotle proceeds to recollection,62 which is distinguished both from continuous actual memory and from the re-learning of what has been completely forgotten. Recollection is the actualising, whether with or without effort, of memory which has become merely potential, i.e. has disappeared from consciousness. The principle on which recollection proceeds is that the movements left in our organs by perceptions tend to succeed each other in regular order. The association of ideas—for this it is of which we have here almost the earliest formulation63—proceeds by similarity, by contrariety, or by contiguity; the recollection of an object tends to be succeeded by the recollection of what is like it or contrary to it or was contiguous to it in the original experience. And this principle, which operates in involuntary recollection, is the guide to be adopted in voluntary recollection. Aristotle proceeds to give an interesting detailed account of the process of recollection, and of the part played in it by the sense of distance in time.
(3) Dreams.64 The fact that the content of dreams is sensuous, though the senses are themselves then inactive (for he does not recognise the contribution made to the fabric of dreams by present sensations), shows, Aristotle maintains, that dreams are the work of imagination, i.e. are a by-product of previous sensation. In the absence of stimulus from without, the mind is more free to attend to images, and at the same time more liable to be deceived by them, since (a) it has not the opportunity which it has in waking life of checking one sense by another, and (b) the critical faculty is in abeyance owing to the pressure of the blood on the heart, the central organ of perception. Thus in sleep we habitually take images for percepts, and to do this is to dream.
To his theory of dreams Aristotle adds an interesting discussion of Divination in Sleep, in which he maintains an admirable balance between credulity and excessive scepticism.
(4) Imagination in relation to desire, and (5) imagination in relation to thought, will be best treated under desire and thought.
MOVEMENT
The four main functions originally recognised by Aristotle were nutrition, sensation, movement, thought.65 We come now to the third of these.66 Is movement originated by the whole soul or by some part, and if the latter, is it by a distinct part which has no other function? It is clearly not due to the nutritive faculty, for it is always directed to an end, and involves either imagination or desire, and is, besides, not possessed by plants. Nor is it due to the sensitive faculty, for many animals which have sensation are stationary. Nor is it due to reason, for reason, even when it thinks about something that should be avoided or pursued, does not necessarily prompt us to avoidance or pursuit, and when it does so, does not always do so effectively; desire seems necessary as well. Nor is it solely due to desire, for self-controlled people obey reason against desire.
Prima facie, then, the causes of movement are desire and practical thought (if we may count imagination as a form of thinking).67 But thought and imagination set us in movement only if they have themselves been set in movement by the object of desire, so that there is really only one faculty that sets us in movement, viz. that of desire. Desire, however, is of two kinds, wish or rational desire, which desires the good, and appetite or irrational desire, which desires the apparent good. Or, to put the antithesis otherwise, wish is for future good, appetite for present pleasure mistaken for absolute pleasure and absolute good. We may distinguish four things involved in the movement of animals68—(1) the object aimed at, which moves without being moved, (2) the faculty of desire, which moves by being moved, (3) the animal, which is moved, (4) the bodily organ by which desire moves the animal, i.e. an organ which, while itself at rest (being ‘moved’ by desire only in the sense of being qualitatively changed), moves the adjacent parts by pushing or pulling. Aristotle illustrates this by the action of the joints, in which one of the contiguous surfaces is at rest, the other in rotatory movement, i.e. at the same time pushed and pulled69; but the ultimate organ which originates movement is for him the heart, which is the pivot of the whole body, the point at which body is actuated by soul.70
Desire is thus the cause of movement. But desire presupposes imagination of good or pleasure to be attained— imagination which may be calculative (i.e. deliberative) or merely sensitive.71 In the latter case the animal acts on the vague ‘imagination’ as soon as it arises (and even the lowest animals have in this sense imagination and desire); in the former the imagined goods are measured against each other. There are three possibilities: (1) unreasoning action from appetite, (2) alternate victory of appetite over wish and of wish over appetite (i.e. incontinence72), (3) action from the ‘naturally higher’ desire, viz. wish.73
Desire, then, and bodily movement may be regarded as secondary effects of sensation. The four main faculties are thus reduced to three—nutrition, sensation, thought. To the last we now proceed.74
THOUGHT
Thought is receptive of intelligible form, as sense was of sensible form.75 It must have no positive form of its own, for this would hinder its being assimilated to its object; its only nature is that it is a capacity; it is nothing actually before it thinks. It must therefore be entirely independent of the body; if it were not, it would have a particular quality before it actually thought. It is the faculty by which we grasp essence, while sense is that by which we grasp essence-embodied-in-matter.
Two objections may be raised to this account. (1) If reason has nothing in common with any of its objects, how can it know -knowledge being a mode of being acted on ? (2) If reason is itself knowable, then (a) if it is so by its own specific nature, and the knowable is all one in species, other things that are known must be knowable through having an admixture of reason in them; while (b) if it is not by its own specific nature that it is knowable, it must have an admixture of the quality which makes other things knowable. The first difficulty Aristotle solves, like the similar difficulty about nutrition and sensation, by saying that reason is at first only potentially identical with its objects (as a wax tablet potentially contains what is later to be written in it), and becomes its objects actually only in knowing them. The second he answers by accepting in a sense the second alternative—by saying that the mind is knowable in the same way as its objects. In knowing immaterial forms, mind is one with its object; the whole mind is filled with the whole object, there being nothing in the object which mind cannot apprehend, and no part of the mind that is not occupied with the object; thus in knowing its object mind is knowing itself. Mind, then, has in it the same quality that makes other things knowable, but this is not an alien admixture but just the quality of being form without matter, which is mind’s essential nature. We can thus reject the first alternative. External things have not mind in them, since they are concrete things in which forms are only implicitly present, while it is with pure forms that mind is potentially identical.
Thinking is divided into two main kinds.76 There is (1) the thought of what is undivided, under which Aristotle considers (a) what is actually undivided in quantity though divisible, i.e. magnitudes within which we could distinguish parts if we chose. Until we do so choose, these are apprehended by a single act of mind in an undivided though divisible time. (b) What is indivisible in kind, an infima species, is also apprehended in an undivided time and by an undivided act of the soul. (c) What is indivisible in magnitude, e.g. a point, is known by an act of negation. The point is known simply as that which has neither length, breadth, nor depth, the line as that which has no breadth nor depth, the moment as that which has no duration, etc. From the apprehension of any of these kinds of undivided object—what we may call direct intuition—is distinguished (2) the other type of knowledge, the judgment, which unites two concepts and at the same time analyses a given whole into its two elements of subject and attribute. And as in sense we had the distinction between the infallible perception of the special sensibles and the fallible perception of the common sensibles and the incidentals, so here Aristotle points out that while judgment is fallible, direct intuition -the apprehension of the essence of a single object— is not.
Aristotle proceeds to show how reason is related to imagination.77 A thought is not an image, but we cannot think without images.78 More definitely, ‘the faculty of thought thinks the forms in the images.’79 An image is a particular mental occurrence, just as much as is a sensation; thought first occurs when the mind discerns a point of identity between two or more images.80 But even when a universal has thus been grasped, it is Aristotle’s doctrine that imagery is still needed by the mind. ‘The soul never thinks without an image.’ Just as in geometrical proof, though we make no use of the particular size of the triangle, we draw one of a particular size, so in thought generally, if we are thinking of something non-quantitative, we yet imagine something quantitative, and if our object be something quantitative but indefinite, we imagine it as of a definite quantity. Nothing can be thought of except in connexion with a continuum, and nothing, however timeless, can be thought of except in connexion with time.81 Aristotle seems here to be setting himself against Plato’s view, expressed in the Divided Line,82 that while scientific thought needs the aid of imagery, philosophical thought deals with pure forms without any such assistance. The use of imagery is the price, Aristotle maintains, which reason has to pay for its association with the lower mental faculties.
ACTIVE AND PASSIVE REASON83
We must finally consider the culminating point of Aristotle’s psychology. ‘There must be,’ he maintains,84 ‘within the soul a distinction answering to the general distinction between the matter which underlies each class of things and is potentially each of them, and the efficient cause which makes them—the distinction of which that between an art and its material is an instance.’ Two points are here to be noticed. (1) The distinction between the active and the passive reason falls within the soul.85 This is fatal to any interpretation which identifies the active reason with a divine reason falling entirely outside the individual human being. It is not fatal to the view that the active reason is a divine reason immanent in human souls. The chief difficulty to which such a view is exposed is that the only passage in which Aristotle deals explicitly with the divine nature—Book A of the Metaphysics—describes God in language which does not suggest immanence. (2) The active reason is not a reason which creates out of nothing. It works on a material given to it, which it promotes from potentiality into actuality.86 What is meant by this we must try to see from the sequel. ‘The one reason,’ Aristotle proceeds, ‘is analogous to matter because it becomes all things; the other is analogous to the efficient cause because it makes all things.’ The first of these statements points to the ordinary action of apprehension. Just as the sensitive faculty becomes its objects in the sense that their form is conveyed over to the sensitive subject and becomes the whole nature, for the time being, of the sensitive subject, so in knowledge reason becomes identical with its objects. The act of apprehension is ascribed, then, to passive reason. What role is ascribed to active reason? In what sense does it make all things? Art makes its objects by making the material become them. And if the analogy is meant to be exact, the role of active reason must be to make passive reason become its objects by apprehending them. We shall see here an instance of Aristotle’s general principle that ‘what is potentially comes to be actually by the agency of something that already is actually.’87 It is obvious that we come to know things which in the ordinary sense we did not know before. How, Aristotle asks himself, can this happen? Does not this transition from potential to actual knowledge imply that there is something in us that actually knows already, some element that is cut off from our ordinary consciousness so that we are not aware of this pre-existing knowledge, but which is nevertheless in some sort of communication with the ordinary consciousness or passive reason and leads this on to knowledge? And when Aristotle refers88 to the moments in which we can live a life like that of God, he will (on this interpretation) be thinking of moments in which the partition between active and passive reason is broken down and we become aware of our oneness with the principle whose knowledge is always actual and always complete.
According to this line of thought, what the active reason acts on is the passive reason, which is a sort of plastic material on which active reason impresses the forms of knowable objects. But in the same sentence Aristotle introduces another line of thought, which seems to have been suggested by Plato’s use of the sun as a symbol for the Idea of Good.89 The one reason is analogous to matter by becoming all things, the other is analogous to the efficient cause by making all things, in the manner of a positive state like light; for in a sense light makes the potentially existing colours actually existing colours. Some of the conditions of colour are present in the dark, but to make actual seen colours a further condition is necessary, viz. light; and active reason is to the intelligible as light is to the visible. The analogy of light must not be pressed too closely. Active reason is not a medium between passive reason and its object; knowledge is a direct not a mediate relation, in Aristotle’s view. But, though not a medium, active reason is a third thing, besides passive reason and the object, which has to be taken account of if we would understand the fact of knowledge, as light is a third thing, besides the eye and the object, which we must take account of if we would understand the fact of sight. Light is the condition of a medium which has been made actually transparent by the presence of an illuminant,90 and it is its actuality that makes it possible for the eye which can see actually to see, and for the visible object actually to be seen. Similarly, the fact that active reason already knows all intelligible objects makes it possible for the passive reason, in itself a potentiality, actually to know, and for the knowable actually to be known.
‘The active reason’, Aristotle continues, ‘is separable and impassible and unmixed, being’ (i.e. because it is) ‘an actuality. For the active is always of higher worth than the passive, and the originative source than the matter.’ The meaning of ‘separable’ here is to be gathered from the occurrence later of the expression ‘when it has been separated.’ It means that the active reason, united for a time with the passive, can be separated from it; and the reference is clearly to the destruction, at death, of the latter and the survival of the former. Elsewhere91 Aristotle speaks of ‘reason,’ simply, as surviving death, but that is where the distinction between active and passive reason is not present to his mind; when it is present he evidently thinks of the passive reason as being, like sense and imagination, an integral part of the soul which is the actuality of a particular body and cannot survive it. The other phrases used, in this sentence, of active reason emphasise the facts that it is entirely independent of the body and that it contains no unrealised potentialities but knows always what it ever knows.
‘Actual knowledge,’ Aristotle proceeds, ‘is identical with its object; potential knowledge is prior in time in the individual, but in general it is not prior in time; reason does not at one time function and at another not.’ We have seen above that in some sense active reason is ‘in the soul’, but we are not conscious of it, or are so only in moments of illumination; thus, in some sense, in the individual potential knowledge comes before actual knowledge. But ‘on the whole’ it does not; active reason knows actually when passive reason as yet knows only potentially. It is clearly implied that active reason, though it is in the soul, goes beyond the individual; we may fairly suppose Aristotle to mean that it is identical in all individuals.
‘When it has been separated it is that only which it is essentially, and this alone is immortal and eternal (we do not remember, however, because this is impassible and the passive reason is perishable); and without this nothing knows.’ Though active reason is always impassible, and unmixed, it is implied that its true nature is obscured during its association with the body, but exists in its purity when this association is over. Does this imply that the disembodied reason is conscious, as the embodied reason is not, of the full extent of its knowledge?
The perplexing remark ‘we do not remember’ receives some light from a passage earlier in the book, in which Aristotle is speaking of the influence of old age on the mental life.92 ‘Intuitive thought and contemplation, then, die away through the destruction of something else within (the body), but are themselves impassible. But reasoning, and loving or hating, are affections not of reason but of its possessor, in so far as he possesses it. Hence when he perishes there is neither memory nor love; for these belonged not to reason but to the composite being which has perished; reason is doubtless something more divine and is impassible.’ In the light of that passage it seems clear that Aristotle here means that memory does not survive death. The ground is that (1) active reason is impassible; it takes no impress from the circumstances of life; its knowledge has therefore no marks of date or circumstance: while (2) the passive reason which does take the impress of circumstances has perished at the death of the individual.
The last words of the chapter are capable of a variety of interpretations, viz.:
- ‘and without the passive reason the active reason knows nothing.’
- ‘and without the active reason the passive reason knows nothing.’
- ‘and without the passive reason nothing knows,’
- ‘and without the active reason nothing knows.’
It can be easily seen that on none of these interpretations do these words properly form part of the ground for our ‘not remembering.’ They simply sum up the teaching of the chapter by saying ‘and without the active reason nothing knows.’
Alexander identifies the active reason with God, and this view is adopted by Zabarella, whose argument93 may be summarised as follows: ‘The active reason is clearly stated to exist entirely apart from matter.94 Now in Metaphysics A, the only place where Aristotle discusses deliberately what pure immaterial forms there are, the only such forms that he recognises are God and the intelligences. The active reason cannot be any of these inferior beings, for these have, apparently, the sole function of moving their respective spheres. The active reason, then, must be God, who as the ‘primary intelligible’95 is the source of intelligibility in all other intelligibles. It is God, then, as active reason, that makes the potential object of knowledge an actual object of knowledge, and at the same time enables the passive reason, which in itself has only the potentiality of knowledge, actually to know, just as the light of the sun causes the potentially visible to be actually visible and the potentially seeing eye actually to see.’
Zabarella’s opinion is always worthy of the most serious attention, But it would seem that in his zeal to get a perfect agreement between the De Anima and the Metaphysics he has put a somewhat unnatural interpretation on the former work. The active reason is distinctly presented there as existing in the human soul. And 
which he takes to mean ‘separate’, more probably means ‘separable’; the mode of being of active reason during the life of the individual seems to be contrasted with its state when it exists
after the death of the individual. Further, it is difficult to suppose with Zabarella that it is in its character as 
rather than as
that it is represented as making the individual’s knowledge possible.
A representation of God in the De Anima as immanent in the individual would not necessarily be inconsistent with the representation of Him in the Metaphysics as transcendent. But a description of Him as having all our knowledge before we have it, and imparting it to us, would be inconsistent with the description of Him in A as knowing only Himself. It is possible that the two books represent divergent modes of Aristotle’s thought about the Deity. But it is not necessary to suppose this. Aristotle makes no actual mention of God in this passage of the De Anima, and though the pure never-ceasing activity of thought here described is in some respects like that ascribed to God in the Metaphysics, Aristotle probably did not identify the two. It is more probable that he believed in a hierarchy reaching continuously from the lowest beings, those most immersed in matter, up to man, the heavenly bodies, the intelligences, and God; the active reason in man being one of the highest members of this hierarchy but having others as well as God above it. This is the interpretation of the De Anima to which the purely deistic doctrine of the Metaphysics points.96
NOTES
1 De An. 402 a7.
2 402 a10–b8.
3 414 b2–4, 415 a3–6, 435 a12.
4 Beare, Greek Theories of Elementary Cognition, 230 f. Cf. De An. 429 a2.
5 Hamlet’s ‘Sense, sure, you have, Else could you not have motion’ (iii. 4. 71), probably goes back to Aristotle (G.G.Greenwood in Class. Rev., xvii. 463 f.).
6 413 a22–a27, 414 a29–415 a12.
7 III. 12, 13; De Sensu, 436 b10–437; Met. 980 a21–b25.
8 403 a3–5.
9 403 a5–b19, 412 b6–9, 413 a4–9.
10 407 b24.
11 G.A. 736 b28.
12 430 a22; cf. the hints in 413a 4–7, b24–27.
13 E.g. 429 b6, 430 a3.
14 429 a27, 432 a2.
15 411 a26 ff.
16 432 b5, 433 a22–25, b28.
17 E.N. 1139 b4.
18 Aristotle points out elsewhere (415 b7–28) that soul is not only the actuality or formal cause of the body but (in accordance with the general principle of the identity of formal, final, and efficient cause) its final cause and the efficient cause of all the changes it originates, whether of place, of quality, or of size.
19 II. 4.
20 Cf. p.105 n. 3.
21 II.5.
22 417 b6, 16.
23 246 b2, 247 a2.
24 246 a18–20.
25 424 a32–b18.
26 424 a5, 432 a16; An Post. 99 b35 ff.
27 425 b22.
28 424 a18.
29 424 a2–10, 26–b1, 426 a27–b8, 429 a29–b3, 435 a21.
30 Why not softness also?
31 435 b7–19.
32 425 b25–426 a27; Cat. 7 b35–8 a12; Met. 1010 b31–1011 a2. Cf. p. 162 f.
33 II. 6.
34 418 a10.
35 De Sensu, 442 b5–7.
36 418 a17, 425 a15; De Sensu, 437 a9, 442 b5; De Mem. 450 a9, 451 a17; cf. De An. 433 b7.
37 II. 7–11; De Sensu, 3–5.
38 422 b19–23, 34–423 a17, 423 b1–26.
39 II. 7. Cf. H.W. B. Joseph in Class. Rev. XVIII. 131 f.
40 Even of phosphorescent objects the ‘proper colour’ cannot be seen in the dark, 419 a2–6.
41 438 a12–16, b5–16, 439 a21–b14.
42 It is found in 425 a27; De Mem. 450 a10; P.A. 686 a31; cf. De Mem. 455 a15.
43 418 a10–20, 425 a13-a11, 428 a22–30; De Sensu, 442 a4–10; De Mem. 450 a9–12, 451 a16, 452 b7–13.
44 425 a15.
45 418 a21.
46 425 a22–b4.
47 425 b12–25; De Somno, 455 a12–17; cf. 429 b26–29, 430 a2–9 on the self-knowledge of reason.
48 Cf. Plato, Charm 168 d, e.
49 E.N. 1170 a25–b10.
50 Met, 1074 b34.
51 426 b12–427 a14.
52 De Sensu, 447 b17–448 a19, 448 b17–449 a20.
53 De Somno, 454 b25–27, 455 a20–b13.
54 455 b28–458 a25.
55 455 b14–28.
56 427 b27–429 a9.
57 428 a24–b9; De Insomniis, 458 b28, 460 b3–27.
58 428 b18–30.
59 De Insomniis, 459 b7, 461 a3–8 25-b15; P.A. 659 b17–19; G.A. 744 a3. For Aristotle’s reasons for regarding the heart, not the brain, as the central sense-organ, cf. De Somno, 458 a15; De Juv. 467 b28 ff.; De Vita, 469 a4–23; De Resp. 478 b33 f.; P.A. 666 a14 ff.; G.A. 781 a20 ff. In this respect he was reactionary, and his mistake retarded knowledge for centuries.
60 De Insomniis, 459 b5 ff.
61 De Mem. I. On Aristotle’s theory of memory and recollection, cf. Bergemann in Arch. f. Gesch. d. Phil. VIII. 342–352.
62 De Mem. 2.
63 Aristotle is to some extent anticipated by Pl. Phaedo 73d–74a.
64 De Insomniis, 1–3.
65 413 a23, b11–13.
66 III. 9.
67 III. 10.
68 Cf. the analysis of nutrition, 416 b20–29.
69 Phys. 244 a2; M.A. 698 a14–b7.
70 P.A. 665 a10–15.
71 433 b29, 434 a5–10.
72 More properly, in the language of the Ethics, alternate incontinence and continence.
73 434 a12–15.
74 III. 3–8.
75 III. 4.
76 III. 6.
77 III. 7, 8.
78 427 b14–16, 431 a16, 432 a7–14; De Mem. 449 b31.
79 431 b2.
80 434 a9, cf. An. Post. 100 a4–16; Met. 980 b28–981 a12.
81 De Mem. 449 b30–450 a9.
82 Rep. 510 b–511 d.
83 Aristotle speaks of ‘passive reason’ but does not actually use the phrase ‘active reason.’
84 iii. 5.
85 
can hardly mean only ‘in the case of the soul.’ And a temporary union of the two reasons within one personality is implied 
1. 22. So, too, Theophrastus says (ap. Them. 108, 23)
86 So Theophrastus describes active 
that which sets passive 
to work (ap. Prisc. 29, 14, ap. Them. 108, 24).
87 Met. 1049 b24.
88 Met. 1072 b14, 24; E.N. 1177 b26–1178 a8, 1178 b18–32.
89 Rep. 507b–509d.
90 418 b12.
91 Met. 1070 a26.
92 408 b24–30.
93 De Reb. Nat., De mente agente, capp. 12, 13.
94 De An. 430 a17.
95 Met. 1072 a26–32.
96 Good accounts of the various interpretations may be seen in Hicks’s ed. of the De Anima, 1xiv–1xix; Adamson, Development of Gk. Phil. 249–254; Webb, Studies in the Hist. of Nat. Theol 264–273; Kurfess,Zur Gesch, d. Erklärung d. Arist. Lehre vom sog.
u.
