This essay deals with the concept of self as it was conceived by the modern philosophers such as Descartes, Hume, and Kant. Modern philosophers understood this concept in essentially two different senses. While the empiricists conceived self as an object, the rationalists saw it as a subject. On the other hand, Kant, who was neither an empiricist nor a rationalist, understood self in its both senses. The ontological status of the concept of self cannot, of course, be separated from its epistemological status, that is, from how it is known. While the rationalists such as Descartes, Spinoza, and Leibniz thought that self-knowledge is the most certain knowledge, the empiricists such as Hume thought that self-knowledge is no different from all other knowledge in terms of certainty. Kant, on the other hand, tried to syntesize these two different poles by separating the objective aspect and the subjective aspect of the self.