This chapter discusses Emmanuel Kant’s works essential to his philosophy as a system, and also illustrates his position in the history of thought. He was first of the Rationalist, or dogmatic school, as he afterwards called it. To Kant there are two kinds of factors present in knowledge. Firstly, that which is given through sense—the a posteriori factor; and secondly, the pure forms of sensibility and understanding. Kant, after following closely the scientific progress made in his time, and pondering on the Rationalist and Empirical theories of Knowledge, sees that both are inadequate in their explanation of empirical science. Astronomy was pre-eminently a science which involved both observation and the apprehension of necessary relations; and whilst both the Empiricist and Rationalist theory of Knowledge each respectively accounted for one of the factors, neither successfully accounted for both in conjunction. The Rationalists contended that Empiricism gave no satisfactory explanation of the necessity contained in mathematical judgments and certain propositions in physics.