Descartes says the mind is distinct from the body, or anything physical for that matter. He says, a thinking substance is nonphysical or spiritual in nature (mind), and an extended substance is physical, but not capable of consciousness or thought (body). However, this very claim is also his biggest problem as his mind body interaction has many critics and to some, can seem invalid. This is mainly due to the challenge by those who ask how mind and body can interact if they are two different substances altogether. Over Descartes' period of teaching, he has conceived many arguments to support his view of the distinction of mind from body. Again, this was not done without its' skeptics.
To examine Descartes' arguments thoroughly, it is important to begin with "The Cogito". This is that he is sure he exists. However, he raises the possibility of someone only making him think he exists.
"Let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something."
"I think I Exist". The cogito is what Descartes' was absolutely certain of. He can't be sure of anything except for the fact that he can think if he can think, he must exist as a thinking being. Descartes' regards "The cogito" to have the mark of knowledge present in its theory - clarity and distinctness of perception.
One of his arguments for the real distinction of mind from body also held clear and distinct perception. This is the Argument of Doubt. While Descartes is unsure of the true existence of his body, he cannot doubt that his mind does indeed exist as he is a thinking thing doubting his very own existence. Therefore, through this certainty, Descartes says that he, an existing substance is not the same as his body as it does not exist. However, this is clearly not a valid argument as it does not show much logic in its statement of his body not existing. By Leibniz's Law, two substances being identical mean that the two substances are the same. For me to say I like Tony Blair but do not like the Priminister is unclear as they are the same person. Similarly is the Masked Man fallacy in which he is certain his father is his father, but not certain his father is the masked man concluding that his father is not the masked man. But that is just his thinking and proves invalid as he thinks of his father (one substance) differently to the way he thinks of the masked man (another substance). However, the masked man could be his father. This helps criticize Descartes' view of the distinction between mind from matter. How can a thinking substance and an extended substance interact the way they do if they are two different kinds of substances? How do I feel hungry (mental event) when my body needs food (physical event)?
Like the argument of doubt, the argument for clear and distinct understanding is also subject to many interpretations and criticisms. Descartes' speaks of his distinction between his mind and body and makes note that his mind is indivisible, whereas his body is divisible. To Descartes' his mind is one united thing, in turn, it is one indivisible thing. Opposite to this is his body which he sees as consisting of different parts and being separable to him. And so his body, if it exists is distinct from his mind. Descartes argues that, if X can exist apart from Y, and vice versa then the two are distinct from each other in every way. He continues, that if he can distinctly understand the possibility that X and Y exist independently, then God can make this so. Clearly, his mind (X) is distinct from his body (Y) as the need for thought belongs to his mind and the need for extension belongs to his body . However, this argument is to a degree flawed as, according to this theory, our only objective is to think. This argument has also had its critics....