Immanuel Kant's Critique of Pure Reason revolutionizes philosophy by exploring the limits of human knowledge. Kant argues that our understanding is shaped by both sensory experience and innate categories, bridging empiricism and rationalism. He introduces the distinction between phenomena (things as we perceive them) and noumena (things-in-themselves), emphasizing that knowledge is confined to appearances. This work fundamentally questions the scope and nature of human cognition, influencing modern philosophy profoundly.