Kant holds that two faculties are required for Erkenntnis – that is, an important epistemic state, sometimes translated as ‘knowledge’ or ‘cognition:’ the understanding and sensibility. Accordingly, he criticizes Leibniz for denying this and holding instead that there is a single cognitive faculty (i.e., “faculty monism”). These essays concern the role of sensibility and intuitions in Kant’s theory of cognition, as well as his criticism of Leibniz’s faculty monism.

In Chapter 1, I provide an account of faculty monism in Leibniz and the Leibnizians Wolff and Baumgarten. I argue that Leibniz provided a framework and terminology which was developed much more fully by Wolff and Baumgarten. In their work, faculty monism became a serious research program, with its own distinctive commitments, predictions, and challenges.

In Chapter 2, I reconstruct three fundamental notions in Kant’s philosophy of mind: representation, consciousness, and cognition. Commentators often hold that cognitions are transparent to the cognitive subject. I argue that this is not the case. These notions are instead continuous with the usage of Leibnizian philosophers. An important upshot: since intuitions and concepts are said to be cognitions, both encode information about objects.

In Chapter 3, I provide a novel account of the nature of intuitions based on two claims: First, unlike concepts, intuitions depict their objects, that is, there is an isomorphism between the representable features of the object and the intrinsic features of intuitions as vehicles. Second, intuitions are thoroughgoingly determined representations: they represent all the representable features of their objects. This suggests the historical claim that Kant was influenced by Leibnizian debates about the nature of singularity in his theorizing about intuitions.

The takeaway is that Kant’s faculty dualism is an innovation and improvement over Leibniz’s monism: the former alone allows for cognition of singular objects, and hence truth.