The Weakest Part of the Book

There is a passage in the Critique of Pure Reason where Immanuel Kant stops lecturing and asks you, directly, about a triangle. Paul Guyer has spent a career with that passage, and in this episode he takes it apart: what it proves, what it merely assumes, and what a determined skeptic could do with its own logic. There is also Moses Mendelssohn, whose objection about time followed Kant for years. By the end, Guyer has named the weakest part of this famous book and told you the one thing its metaphysics was really for. Neither answer is where you think.