Kant and Sartre on self-knowledge
The similarities between the Copernican and existentialist approach to self-knowledge can be clearly summarized by the combined effect they have on the correspondence model of self-knowledge. The self-knower who holds that knowledge conforms to its object is not only wrong but deceived if his goal is the complete one-to-one correspondence between, on the one hand, objectively validated propositions, and on the other an independently existing, recalcitrant reality (the Self). Both Kant and Sartre hold that we can know ourselves in terms of appearances or quasi-objects, but they both deny that we can know what we "really" are over and above the empirical, contingent and finite knowledge we have. For Kant, this is because we are, most fundamentally, something unknowable; for Sartre, it is because we are, most fundamentally, nothing. In both cases, the self we purport to know is in an important sense other than itself: in saying "I," more is being said than we know — and less. The "I" is spoken only through and across that which is not "I."
Jopling, D. (1986). Kant and Sartre on self-knowledge. Man and World 19 (1), pp. 73-93.
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