It is a commonplace that Nietzsche makes heavier use of metaphor than most philosophers. But the boundaries between metaphor and literal language are unclear, especially when Nietzsche uses biological terms. Recent commentators, anxious to avoid biological reductionism, have interpreted such terms as purely metaphorical. But recent studies suggest that Nietzsche worked within a nineteenth-century intellectual context that may be called 'biologism,' which saw biology as providing models for processes in other areas of life, but did not reduce them to biology. To test this insight, the present article examines particularly the metaphors (or apparent metaphors) used for processes of change in The Genealogy of Morals, showing how Nietzsche draws on two branches of scholarship that he especially valued: philology and biology. At certain difficult points in Nietzsche's argument, these metaphors come under strain, especially when Nietzsche applies a whole series of incompatible metaphors to explain (or seem to explain) the development of 'slave morality.' **********
