This chapter examines Russell’s appreciation of the relevance of psychology for the theory of knowledge, especially in connection with the problem of the external world, and the background for this appreciation in British philosophy of the eighteenth and nineteenth centuries. Russell wrote in 1914 that “the epistemological order of deduction includes both logical and psychological considerations.” Indeed, the notion of what is “psychologically derivative” played a crucial role in his epistemological analysis from this time. His epistemological discussions engage psychological factors (...) in the perception of external objects that had been closely examined in the nineteenth century, among other places in J. S. Mill’s response to William Hamilton’s conception of knowledge of the external world. These considerations came to Russell in various ways, including his contact with British Empiricism (Mill, with Berkeley, Hume, and Reid as background), his engagement with Austrian philosophy, his close acquaintance with the philosophy and psychology of William James, and his exposure to contemporary British writings concerning the problem of the external world. The latter writings provide a crucial context within which natural scientific psychology came to be seen as distinct from epistemology and yet as relevant to its concerns. (shrink)