Herbert Spencer (1820-1903) was regarded by the Victorians as the foremost philosopher of the age, the prophet of evolution at a time when the idea had gripped the popular imagination. Until recently Spencer's posthumous reputation rested almost excusively on his social and political thought, which has itself frequently been subject to serious misrepresentation. But historians of ideas now recognise that an acquaintance with Spencer's thought is essential for the proper understanding of many aspects of Victorian intellectual life, and the present selection is designed to answer this need. It provides a cross-section of Spencer's works from his more popular and approachable essays to a number of the volumes of the Synthetic Philosophy itself. Volume IV: The Principles of Psychology.