Kant claims that to “pick out from ordinary cognition the concepts that are not based on any particular experience and yet are present in all cognition from experience (for which they constitute as it were the mere form of connection) required no greater reflection or more insight than to cull from a language rules for the actual use of words in general, and so to compile the elements of a grammar” (4:323). The analogy with grammar offers a fruitful way to understand how the categories apply to and structure the materials provided by sensibility and empirical concepts. The categories might be described as providing the rules of a kind of ‘transcendental grammar’ that makes experience possible. Attending to the analogy with grammar reveals that the link between the categories and empirical concepts is far closer than one might initially think, since the content to which the categories apply must be grounded in sensible experience. Grammar does not create new content but rather informs propositions by giving structure to linguistic elements available to speakers of a language; likewise, the categories do not produce new cognition but rather ‘inform’ judgments by giving structure to the sensible contents provided by experience.

Almost every reader’s first encounter with Kant comes through either the Groundwork of the Metaphysics of Morals or the Prolegomena to Any Future Metaphysics, but while the former work occupies a central and revered place in the philosophical canon, the Prolegomena is often viewed much more ambivalently.

The distinction between judgments of perception and judgments of experience has been a source of consternation to many commentators, since Kant’s claim that only judgments of experience involve the application of the categories seems to run afoul of the central doctrine of judgment found in the first Critique, where Kant proposes that all judgments are categorial. This chapter casts the distinction in a new light, by focusing not on whether all judgments must be categorial, but rather on what processes guide the transformation of judgments of perceptions into judgments of experience. Drawing on a comparison Kant makes between the categories and grammatical principles, the essay suggests that the way that categories apply to perceptual content mirrors how grammatical rules structure linguistic content, and that this allows for a new understanding of the role that judgments of experience play in the Prolegomena, and Kant’s critical idealism more broadly.