AbstractFor Darwinism to succed as a general theory of the development of life, if had to account for at least the rudiments of all human characteristics. Thus Darwin and his colleague G. J. Romanes had to make “mental evolution” the basis for scientific psychology. F. Max Müller, Oxford's professor of comparative phiology, drew on Kant' work, Romantic Naturphilosophie, and his views on the history of language and the relation of language to thought to maintain the language showed a difference not in degree but in kind between man and the lower primates. In his debate with Romanes, he argued that the study of language, not Darwinit natural history, should be the basis for a science of human psychology. However, the two authors had such different definitions of the key terms in their discussion that their differences were not only unresolved but irresolv