Thing-in-itself and first philosophy

The distinction which is made between philosophy and the sciences nowadays was between metaphysics and the other sciences in the pre-Kantian history of philosophy. Therefore, the metaphysics was the same thing as the philosophy. Kant's critique of metaphysics led to the disintegration of philosophy. Today, philosophy in its common form is divided into fields such as "philosophy of…". But since philosophy is essentially a universal discipline, the disintegration contradicts its nature. A natural consequence of Kant's criticism of metaphysics has been the "what is philosophy" discussions. Criticisms of metaphysics as the first philosophy or philosophy have revealed various first philosophy candidates. The main reason why the post-Kantian history of philosophy seems incomprehensible and philosophers seem to be doing different activities from each other is that their first philosophies are different. The concept of "thing-in-itself" is very convenient to follow these discussions and to understand the unity of different philosophies. Key Words: Kant, First Philosophy, Thing-in itself