Examines the "transcendental function" of the imagination in Kant. Horstmann argues that the imagination has the task of differentiating from among the totality of a subject's sense impressions those that comply with general conceptual rules and those that are not subject to such rules. The challenge in delineating imagination’s role in this respect is to show how the imagination can have a role distinct from that of the understanding. Nevertheless, Horstmann argues that we pay a steep price for simply subsuming imagination under the understanding. Specifically, it becomes difficult to explain how it is possible that – already at the level of receptive sensibility – material is available that is fit for the synthesizing activities of the understanding. The chapter thus suggests and defends an interpretation according to which imagination has an apprehending function. On this account, imagination transforms mere "sensations" or impressions – non-individuated and unstructured psychological events – into what Kant calls "perceptions," i.e., conscious, contentful representations that constitute the material out of which intuitions are synthesized.