De Anima

So much for the theories of soul handed down by our predecessors. Let us, then, make a fresh start and try to determine what soul is and what will be its most comprehensive definition. Now there is one class of existent things which we call substance, including under the term, firstly, matter, which in itself is not this or that; secondly, shape or form, in virtue of which the term this or that is at once applied; thirdly, the whole made up of matter and form. Matter is identical with potentiality, form with actuality. And there are two meanings of actuality: knowledge illustrates the one, exercise of knowledge the other. Now bodies above all things are held to be substances, particularly such bodies as are the work of nature; for to these all the rest owe their origin. Of natural bodies some possess life and some do not: where by life we mean the power of self-nourishment and of independent growth and decay. Consequently every natural body possessed of life must be substance, and substance of the composite order. And since in fact we have here body with a certain attribute, namely, the possession of life, the body will not be the soul: for the body is not an attribute of a subject, it stands rather for a subject of attributes, that is, matter. It must follow, then, that soul is substance in the sense that it is the form of a natural body having in it the capacity of life. Such substance is actuality. The soul,

therefore, is the actuality of the body above described. But the term "actuality" is used in two senses; in the one it answers to knowledge, in the other to the exercise of knowledge. Clearly in this case it is analogous to knowledge: for sleep, as well as waking, implies the presence of soul; and, whilst waking is analogous to the exercise of knowledge, sleep is analogous to the possession of knowledge without its exercise; and in the same individual the possession of knowledge comes in order of time before its exercise. Hence soul is the first actuality of a natural body having in it the capacity of life. And a body which is possessed of organs answers to this description.—We may note that the parts of plants, as well as those of animals, are organs, though of a very simple sort: for instance, a leaf is the sheath of the pod and the pod of the fruit. The roots, again, are analogous to the mouths of animals, both serving to take in nourishment. If, then, we have to make a general statement touching soul in all its forms, the soul will be the first actuality of a natural body furnished with organs. Hence there is no need to enquire whether soul and body are one, any more than whether the wax and the imprint are one; or, in general, whether the matter of a thing is the same with that of which it is the matter. For, of all the various meanings borne by the terms unity and being, actuality is the meaning which belongs to them by the fullest right.

It has now been stated in general terms what soul is, namely, substance as notion or form. And this is the quiddity of such and such a body. Suppose, for example, that any instrument, say, an axe, were a natural body, its actuality would be its substance, would in fact be its soul. If this were taken away, it would cease, except in an equivocal sense, to be an axe. But the axe is after all an axe. For it is not of a body of this kind that the soul is the quiddity, that is, the notion or form, but of a natural body of a particular sort, having in itself the origination of motion and rest.

Further, we must view our statement in the light of the parts of the body. For, if the eye were an animal, eyesight would be its soul, this being the substance as notion or form of the eye. The eye is the matter of eyesight, and in default of eyesight it is no longer an eye, except equivocally,

like an eye in stone or in a picture. What has been said of the part must be understood to apply to the whole living body; for, as the sensation of a part of the body is to that part, so is sensation as -a whole to the whole sentient body as such. By that which has in it the capacity of life is meant not the body which has lost its soul, but that which possesses it. Now the seed in animals, like the fruit in plants, is that which is potentially such and such a body. As, then, the cutting of the axe or the seeing of the eye is full actuality, so, too, is the waking state; while the soul is actuality in the same sense as eyesight and the capacity of the instrument. The body, on the other hand, is simply that which is potentially existent. But, just as in the one case the eye means the pupil in conjunction with the eyesight, so in the other soul and body together constitute the animal.

Now it needs no proof that the soul—or if it is divisible into parts, certain of its parts—cannot be separated from the body, for there are cases where the actuality belongs to the parts themselves. There is, however, no reason why some parts should not be separated, if they are not the actualities of any body whatever. Again, it is not clear whether the soul may not be the actuality of the body as the sailor is of the ship. This, then, may suffice for an outline or provisional sketch of soul.