The Principle of Reason, the text of an important and influential lecture course that Martin Heidegger gave in 1955-56, takes as its focal point Leibniz's principle: nothing is without reason. Heidegger shows here that the principle of reason is in fact a principle of being. Much of his discussion is aimed at bringing his readers to the "leap of thinking," which enables them to grasp the principle of reason as a principle of being. This...