Kants these über das Sein

Heidegger starts from Kant's claim that "Being is not a real predicate" - that Being cannot be understood as a property that is attributed to a being. Instead, Being denotes an act of affirmation in a judgment: when we say that something "is", we are in fact affirming its presence or existence.

Heidegger develops this idea by arguing that Being is not a particular being or a property of being, but the way in which being shows itself. Being is an act of showing, not an object among objects.

However, Heidegger warns that Kant, although offering important insights, remains within the framework of traditional metaphysics because he does not ask the fundamental question of Being as such. Heidegger uses Kant's thesis to emphasize even more clearly his key idea: Being cannot be understood starting from being, but requires a special, original reflection.

"Kant's thesis on Being" thus represents an important point in Heidegger's effort to break with the metaphysical tradition and open the way to a new way of thinking about Being.