He then tries to define what exactly this ‘I’ that exists is. His first answer is a ‘man’, which he defines as a ‘rational animal’. (Aristotelian answer).But this answer is far too complex for one would have to go on to define rationality and animal and these definitions would lead to other more complex ones. This is not the best way to go about answering the question.
In order to understand what ‘I’ is, he considers the things which came spontaneously into his mind when he first considered the question. His first thought is that he had a body – “That I had a face, hands, arms and the whole mechanical structure of limbs which can be seen in a corpse.” He gives the ‘I’ several characteristics – nourishment, movement, sense-perception and thinking. He attributes these to the soul and imagines this to be made of some tenuous substance like wind or ether which permeates his body. By body he means “whatever has a determinable shape and definable location and can occupy a space in such a way to exclude any other body; it can perceive by touch, sight, hearing, taste or smell and can be moved in various ways, not by itself but by whatever else comes into contact with it.” He contends that the power of self-movement, sensation and thought is foreign to the nature of the body.
Of all of these characteristics, only thought is synonymous with the ‘I’. He cannot be sure of having a body so all characteristics associated with the body are not synonymous with the ‘I’. The same applies to sensory perception, nutrition and movement, as these all require a body. He cannot separate thinking from the ‘I’. He concludes that he can define the ‘I’ as a mind, or intelligence, or intellect, or reason. He cannot use imagination to determine the nature of ‘I’ as using the imagination to determine the nature of things is akin to being awake and seeing the world but having unclear vision and so falling back asleep and believing that simply because vision is clearer in dreams that that is a more true version of reality.
“But then what am I? A thing that thinks. What is that? A thing that doubts, understands, affirms, denies, is wiling, is unwilling and also imagines and has sensory perceptions” All of the attributes stated above all belong to the ‘I’. It is self-evident that thinking, doubting, willing and understanding do. Imagination does too, as even though the things that are imagined are not real, the power of imagination is real and exists as part of thinking. The same applies to sensory perception; they may perceive false things but that power of perception must be true and also exists as a part of the ‘I’. They can be arranged into three categories: those that judge (doubting, understanding, willing, affirms), those that imagine and those that perceive.
At first consideration, it appears that we know the corporeal things better than the ‘I’ but yet we cannot even prove that the corporeal things exist. The wax argument:
We think we know the world through physical sensation, eg touch, sight, smell, etc. It follows that we know wax has a certain colour, shape, size and smell and we identify it through these. But if we melt wax, its physical properties change and our senses detect this change. If we simply knew the world through our senses, we would be unable to recognize that the wax in two different states was still wax. So, we identify things through a different means to our senses. Descartes called this an intellectual perception or understanding....