The Ens Rationis and the Transcendental Problem in Kant’s Opus Postumum

The concept of ens rationis is widely used by Kant in some drafts of his Nachlasswerk. In the first Critique, at the end of the Transcendental Analytic, Kant defines the ens rationis, or “thought-entity” (Gedankending), as a “concept without an object”. My aim is to show that, in Opus postumum, we find a significant shift of the notion of ens rationis, which lead to a redefinition of the transcendental philosophy itself. In the sections named A Elemen. System 1-6 and Übergang 1-14, this notion is used when referring to the ether, thought as a necessary material foundation of the collective unity of experience. The ether is thus not to be understood not as substances existing outside the subject, but rather as the result of a true act of positing. However, it would be quite problematic to conceive it as a mere fiction created by an imaginative action of the subject or, indeed, as a simple concept without an object. Kant writes for example that, although it exists only in thought, the ether has reality (Realität). Therefore, my point is that the status of the transcendental philosophy significantly shifts from a mere inspection of the formal conditions of possibility of experience to an activity which construct experience even from a material standpoint. The “thought- entities” are exactly what conveys this genetic function, and they therefore reveal a status which would be not comprehensible only with the speculative tools of the first Critique.