From a historical point of view the main goal of Kant's transcendental deduction in the Critique of Pure Reason was to show that there are well defined limits for the validity of the synthetic judgements a priori. Since objects of experience are constituted by means of certain categories, the general statements which follow from these categories are a priori valid for all objects of experience, but the a priori validity is also restricted to these objects. "Consequently, there can be no a priori knowledge, except of objects of possible experience."