The paper argues that Plessner's theory of positionality can be traced back to Kant's theory of predicabilia in the Critique of Pure Reason. Kant's theory of predicabilia allows for the reformulation of Plessner's distinction between the organic structure of the living body on the one hand and the positional unity of this living body on the other hand. This enables a concept of non-physical spatiality from which Plessner's concept of the boundary can be derived. Therefore, Plessner's theory of positionality competes neither with Kant's transcendental epistemology nor with his anthropology but rather extends his philosophy of science. Plessner develops the conceptual specifics of living beings, supplementing Kant's concept of matter as the specific object of physics.