# Spencer Herbert Spencer (1820-1903), English philosopher and social scientist. He is known for his application of the scientific doctrines of evolution to philosophy and ethics, with a central principle, the "persistence of force" as the agent of all change, form and organization in the knowable universe. The only limit which Spencer placed on the application of the theory of evolution was in the area which he called the unknowable, the ultimate nature of reality. The content of the unknowable was not only theological but also included such scientific ideas as matter, space, time, motion and force. He proposed a principle of limitation of knowledge in which human thought was confined to that which could be compared with and related to other things.