"Thus much only can we say: 'The image is a product of the empirical faculty of the productive imagination--the schema of sensuous conceptions (of figures in space, for example) is a product, and, as it were, a monogram of the pure imagination a priori, whereby and according to which images first become possible, which, however, can be connected with the conception only mediately by means of the schema which they indicate, and are in themselves never fully adequate to it.'"
— Kant, Immanuel (1724-1804)
(A141-3/B180-2, cf. pp. 273-4 in Cambridge UP edition)
Reading Kant's Critique of Pure Reason, trans. Paul Guyer and Allen Wood (Cambridge: Cambridge UP, 1998).