 In working out his perspective optics of cognition, Nietzsche built on contemporary developments in the theory of cognition—particularly the work of non-orthodox neo-Kantians like Friedrich Lange and positivists like Ernst Mach, who proposed naturalized, psychologically-based versions of the broad type of theory of cognition initially developed by Kant and Schopenhauer (see Clark 1990; Kaulbach 1980, 1990; Anderson 1998, 2002, 2005; Green 2002; Hill 2003; Hussain 2004). The Kantian thought was that certain very basic structural features of the world we know (space, time, causal relations, etc.) were artifacts of our subjective cognitive faculties rather than properties or relations of things in themselves; but where Kant and Schopenhauer had treated these structures as necessary, a priori conditions of any possible experience whatsoever, the more naturalistically oriented figures who influenced Nietzsche sought to trace them to sources in human empirical psychology, which would of course be contingent. The potential of these ineliminable subject-side influences to vary suggests the idea of treating them as a kind of perspective, which Nietzsche found developed in an idealist version by Gustav Teichmüller (1882). Leaving Teichmüller’s idealism to one side, Nietzsche develops the idea by tying cognitively important perspectives back to his own psychology. In particular, the Genealogy passage emphasizes that for him, perspectives are always rooted in affects and their associated patterns of valuation. For that reason, Nietzsche holds that “every great philosophy so far” has been “the personal confession of its author and a kind of involuntary and unconscious memoir” (BGE 6). Thus, theoretical claims not only need to be analyzed from the point of view of truth, but can also be diagnosed as symptoms and thereby traced back to the complex configurations of drive and affect from the point of view of which they make sense. Nietzsche’s perspectivism thus connects to his “genealogical” program of criticizing philosophical theories by exposing the psychological needs they satisfy; perspectivism serves both to motivate the program, and to provide it with methodological guidance.