Page:The Story of Philosophy.pdf/446



The second and third volumes of the Synthetic Philosophy appeared in 1872 under the title of Principles of Biology. They revealed the natural limitations of a philosopher invading a specialist's field; but they atoned for errors of detail by illuminating generalizations that gave a new unity and intelligibility to vast areas of biological fact.

Spencer begins with a famous definition: "Life is the continuous adjustment of internal relations to external relations." The completeness of life depends on the completeness of this correspondence; and life is perfect when the correspondence is perfect. The correspondence is not a merely passive adaptation; what distinguishes life is the adjustment of internal relations in anticipation of a change in external relations, as when an animal crouches to avoid a blow, or a man makes a fire to warm his food. The defect of the definition lies not merely in its tendency to neglect the