work. He strongly disagreed with Comte.

Spencer's second book, Principles of Psychology, published in 1855, explored a physiological basis for psychology, and was the fruit of his friendship with Evans and Lewes. The book was founded on his fundamental assumption that the human mind is subject to natural laws and that these can be discovered within the framework of general biology. This permitted the adoption of a developmental perspective not merely in terms of the individual (as in traditional psychology),