Immanuel Kant’sProlegomena is an indispensable guide through the obscure and convoluted tangle of his “critical philosophy.” It has inestimable value as an introduction to the revolutionary doctrine that he called “transcendental idealism” and clarifies the points made in his greatest and most influential book, the Critique of Pure Reason. The Prolegomena is a pivot of Kant’s revolutions in metaphysics and epistemology.