Immanuel Kant highlights in his works two important distinctions - the one between a priori knowledge and a posteriori knowledge and the one between analytic judgments and synthetic judgments. A posteriori knowledge is the particular knowledge we obtain from our experience, and a priori knowledge is the necessary and universal knowledge we have independent of any experience, such as our knowledge of Mathematics. The a priori knowledge reflects the human’s pure and fundamental need of knowledge. The philosophical works that clearly define the terms of a priori and a posteriori knowledge are:
Critique of Pure Reason, 1781
Prolegomena to any Future Metaphysics, 1783
Metaphysics, 1785