A. N. Whitehead's An Enquiry Concerning the Principles of Natural Knowledge is a searching philosophical challenge to the foundations of science. Written in the shadow of modern physics, relativity, and World War I, it asks what space, time, matter, measurement, and perception really mean when traced back to experience rather than abstract theory. Whitehead argues that nature cannot be understood as matter scattered through empty space and time, or as a series of durationless instants. Instead, reality is a coherent web of events, relations, and extended processes, grasped from within the world by a percipient mind. Drawing on and disputing thinkers from Berkeley and Hume to Kant, Mill, Russell, and Bergson, he develops a demanding "method of extensive abstraction" and a theory of perceptual and physical objects that explains motion, continuity, causation, and change. Chairs, cliffs, stones, and living organisms emerge as stable but inherently vague patterns within nature's larger order. Technical, ambitious, and deeply reflective, this work reimagines scientific knowledge as an active, human, and philosophical encounter with the structure of reality. This edition has been fully restored with modern typesetting, custom cover design.