In this thesis the quiddity of knowledge in Kant&#039 / s critical philosophy has been investigated within the historical context of the problem. In order to illustrate the origins of the subject-matter of the dissertation, the historical background of Kant&#039 / s views on the theory of knowledge has been researched too. As a result of this research, it is concluded that Kant did not invent a new philosophical problem, but he tried to improve a decisive solution for one of the oldest question of history of philosophy i.e., &ldquo / How is synthetic a priori knowledge is possible?&rdquo / The theoretical dimension of Kant&#039 / s theory of knowledge is reserved for this purpose. The above mentioned question is not new neither for us nor for Kant, but his answer and his philosophical stand have clearly revolutionary meaning both for us and for him. This thesis claims that his stand-point not only leads to an original epoch for the theory of knowledge, but creates a serious possibility for a new ontology explicating the quiddity of knowledge.