Critique of Pure Reason a real substance. Unlike Descartes who believes that the soul may be known directly through reason, Kant asserts that no such thing is possible. Descartes declares "cogito ergo sum" but Kant denies that any knowledge of "I" may be possible. "I" is only the background of the field of apperception and as such lacks the experience of direct intuition that would make self-knowledge possible. This implies that the self in itself could never be known. Like Hume, Kant rejects knowledge of the "I" as substance. For Kant, the "I" that is taken to be the soul is purely logical and
Cogito, ergo sum distinctiveness of self-evident propositions — to establish true and justified propositions despite having adopted a method of generalized doubt. As a consequence of this demonstration, Descartes considers science and mathematics to be justified to the extent that their proposals are established on a similarly immediate clarity, distinctiveness, and self-evidence that presents itself to the mind. The originality of Descartes's thinking, therefore, is not so much in expressing the "cogito" — a feat accomplished by other predecessors, as we shall see — but on using the "cogito" as demonstrating the most fundamental epistemological principle, that science and mathematics are justified by