The principles of pure understanding, whether they are a priori constitutive (like the mathematical principles) or merely regulative (like the dynamical principles), contain nothing but only the pure schema, as it were, for possible experience; for this has its unity only from the synthetic unity that the understanding originally and from itself imparts to the synthesis of the imagination in relation to apperception, and in relation to and agreement with which the appearances, as data for possible cognition, must already stand a priori.