The Critique of Pure Reason

Immanuel Kant asks reason to investigate the limits of its own authority in The Critique of Pure Reason. His target is not a survey of earlier books or systems but the faculty that claims knowledge independently of experience. The inquiry therefore places the possibility of metaphysics itself under examination.

Kant distinguishes a priori knowledge, which carries necessity and universality, from a posteriori knowledge gained through experience. A second distinction separates analytic judgments, whose predicates are already contained in their subjects, from synthetic judgments, which add something to a concept. The central problem emerges when he argues that mathematics, foundational natural science, and metaphysics depend on synthetic a priori judgments: how can such knowledge be possible?

Transcendental idealism provides the framework for his answer. Objects as they appear conform to the conditions of human cognition; space and time belong to the sensible form through which they are encountered, not simply to things considered in themselves. Kant develops this position in dialogue with empiricists such as Locke and Hume and rationalists including Leibniz and Wolff. Readers approaching modern epistemology will find a systematic account of what experience can justify, what reason contributes before experience, and where claims to knowledge encounter their boundary.