It was characteristic of the great modern philosophers to attempt, each in his own way, to rebuild philosophy from the ground up. Kant embraced this goal more fully than any other classical modern philosopher. And his work did in fact change philosophy permanently, though not always as he had intended. He wanted to show that philosophers and natural scientists were not able, and would never be able, to give final answers to questions about the nature of the physical world and of the human mind or soul, and about the existence and attributes of a supreme being. While he did not accomplish precisely that, his work changed philosophy's conception of what can be known, and how it can be known. Kant also wanted to set forth new and permanent doctrines in metaphysics and morals. Though his exact teachings have not gained general acceptance, they continue to inspire new positions in philosophical discussion today.

Kant stands at the center of modern philosophy. His criticism of previous work in metaphysics and the theory of knowledge, propounded in the Critique of Pure Reason and summarized in the Prolegomena, provided a comprehensive response to early modern philosophy and a starting point for subsequent work. He rejected previous philosophical explanations of philosophical cognition itself. His primary target was the rationalist use of reason or “pure intellect” – advanced by Descartes and Leibniz – as a basis for making claims about God and the essences of mind and matter.