De Anima

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.