The conditions of experience › Two distinctions that must stay separate

An a priori claim, in Kant's usage, has a justification independent of experience. An a posteriori claim depends on experience. This distinction concerns the basis of knowledge. It does not simply separate beliefs acquired before birth from beliefs learned afterward. Kant treats necessity and strict universality as marks that experience alone cannot supply: observing many cases shows how things have been, without establishing that exceptions are impossible. Introduction I–II.

A second distinction concerns what a judgment says. In an affirmative analytic judgment, the predicate is contained in the subject concept. In an affirmative synthetic judgment, the predicate adds something beyond that containment. Kant illustrates the contrast with bodies being extended and bodies being heavy. In the first case, he regards extension as already included in the concept being analyzed. In the second, heaviness adds a determination requiring a further basis. These examples explain his distinction; they do not show that every philosophically interesting judgment is automatically classified without dispute. Introduction IV.

The difficult combination is the synthetic a priori: a judgment that extends cognition while possessing a basis independent of experience. Kant treats pure mathematics as an example. For him, analyzing the concept of adding seven and five does not by itself produce twelve. We must construct the combination through intuition. His point concerns how the judgment is known, not whether the arithmetic result is correct. A reader can accept that seven plus five equals twelve while challenging his explanation of its epistemic status. Introduction V.

The book's question is therefore more exact than "Does the mind shape experience?" Kant needs to explain how a contribution from the subject can have objective validity. A private association may organize someone's thinking without making a claim true of an object. His argument must establish why the relevant forms and concepts apply to any object we could experience, rather than merely showing that we happen to use them.