Cogito Ergo Sum VIII

Avicenna, Al-Shifa: Soul, I.1 (Hackett Reader 178-9):

So we say that it has to be imagined as though one of us were created whole in an instant but his sight is veiled from directly observing the things of the external world. He is created as though floating in air or in a void but without the air supporting him in such a way that he would have to feel it, and the limbs of his body are stretched out and away from one another, so they do not come into contact or touch. Then he considers whether we can assert the existence of his self. He has no doubts about asserting his self as something that exists without also asserting the existence of any of his exterior or interior parts, his heart, his brain, or anything external. He will, in fact, be asserting the existence of his self without asserting that it has length, breadth, or depth, and, if it were even possible for him in such a state to imagine a hand or some other extremity, he would not imagine it as a part of his self or as a necessary condition of his self - and you know that what can be asserted as existing is not the same as what cannot be so asserted and that what is stipulated is not the same as what is not stipulated. Thus, the self whose existence he asserted is his unique characteristic, in the sense that it is he himself, not his body and its parts, which he did not so assert. Thus, what one has been alerted to is a way to be made alert to the existence of the soul as something that is not the body - nor in fact any body - to recognise it and be aware of it, if it is in fact the case that he has been disregarding it and needed to be hit over the head with it.