In his monumental Critique of Pure Reason, German philosopher Immanuel Kant (1724–1804) argues that human knowledge is limited by the capacity for perception. He attempts a logical designation of two varieties of knowledge: a posteriori, knowledge acquired through experience, and a priori, knowledge not derived through experience. Kant maintains that the most practical forms of human knowledge employ a priori judgments that are possible only when the mind determines the conditions of its own experience. A cornerstone of Western philosophy, this seminal treatise was originally published in 1781. Kant, whose life was dedicated to a quiet and passionate quest for truth, expresses herein his unique system of philosophical thought, and his approach, known as transcendental idealism, based on meticulous investigations of metaphysics, ethics, and aesthetics. This translation by J. M. Meiklejohn offers a simple and direct rendering of Kant's work that is suitable for readers at all levels.