The article introduces Kant’s doctrine of schematism (Critique of Pure Reason A 137-A 147; B 176-B 187). The inclusion of the chapter on schematism in the ‘Doctrine of the Principles’ rather than the ‘Doctrine of Concepts’ is taken as a clue to distinguishing the Doctrine of Schematism from the Deduction of the Pure Concepts of the Understanding. This provides clarity on the function of schematism. The author conceives of schematism as something entirely new to the Transcendental Deduction of the Categories, namely, as preparation for the use of categories as predicates in sentences known as the ‘Principles of Understanding’ referring to phaenomena (appearances in time and space) rather than the undetermined concept of objects in general. To support this interpretation, the author addresses main concepts of the schematism theory (for instance, those of schema, imagination, homogeneity, and time-determination) and describes the function of schematism. Imagination is presented as an instance of the function usually called “understanding” when directed towards appearances given in time and space. Understanding becomes imagination when it obeys not only the laws of logics, but also the laws of time. Homogeneity (a concept that plays an important role in the theory of schematism) is explained with reference to Tetens’s Philosophical Essays on Human Nature (1777). The explanations of concepts provided in the article are not exhaustive. They are discussed in more detail in the author’s earlier publications referred to in the footnotes. The article also discusses earlier and contemporary literature on schematism.