Let me begin by explaining the theory of the real distinction of mind from body.
Rene Descartes was a dualist, he believed that the mind is an immaterial thing and is distinct from the body. He believed that the mind is not the body, is not dependant upon the body and so can exist without the body. It is however my opinion that Descartes is not saying 'when the body dies the mind will endure and exist separately' (it might very well have those connotations) but I feel he is saying that if the body had never existed in the first place there could still exist the mind.
In order to form a basis from which Descartes can construct his arguments for the real distinction of mind from body, he first looks for an absolute, a fact which is undeniable, a point from which an argument can grow, and provided the premise always semantically entails the conclusion, as the first premise is true so to must any final conclusion.
In order to do this Descartes says that he shall "reject as absolutely false" everything for which he "could imagine the least ground of doubt"1
This would imply that Descartes refused to accept any idea or thought as true if that truth could be subject to any possible doubt. It then followed that Descartes found that he was able to doubt that any of his perceptions corresponded to the corporeal world in which they appeared i.e. he could imagine that nothing he perceived was true. Indeed he could doubt that he is part of this reality, a reality which is based on material objects, he could also doubt the fact that he had a body and yet he could not conceive that he did not exist, whatever 'He' may be. "I...