Descartes says that the proposition "I exist" is certain, because of the theory he uses in the first meditation. If we think we exist, then were thinking period. So even if we think we don't exist, then that proves that were still thinking, therefore we must exist. Russell wants to disagree with Descartes by saying that the "I", as Descartes uses it, stands for the self, but for Russell the self is an object. So Russell is trying to point out that if the self is an object, and objects are always in flux, then there is a possibility that ....