Why Is Freedom the Keystone of Kant's Philosophy?

Immanuel Kant wrote three massive Critiques, on knowledge, on morality, and on judgment, and they can look like three separate mountains. Paul Guyer, who has translated and interpreted all of them, insists they form a single arch, and that one idea is the keystone holding the whole structure up: freedom. "Freedom is the inner value of the world," Guyer quotes Kant as writing. "Freedom is that which confers value on everything else." The reason is structural: the theory of knowledge exists, at bottom, to make room for freedom; the moral law presupposes it; human dignity rests on it. Understand why Kant thought that, and the entire system snaps into focus.