  It is not, however, only Lange’s in-principle restriction of knowledge to appearances that Vaihinger wishes to champion. More importantly, he holds that Lange has demonstrated that the empirical sciences themselves conclusively support the transcendental idealist’s position. In Chapter IV, Part 3 of the second volume of his magnum opus The History of Materialism and Critique of its Contemporary Significance, Lange draws on the work of Johannes Müller and Helmholtz to argue that “the physiology of the sense organs is the developed, or corrected Kantianism, and Kant’s system can, as it were, be viewed as a program for the more recent discoveries in this field” (1873–75, 2:409). The basic idea was that such research had shown that our perceptual apparatus plays an active role in structuring our experience, and that the output of such a process does not qualitatively resemble the initial external stimulus, for which it is a mere “sign.” Since what we perceive is always the product of such unconscious physiological processes, it supposedly follows that we have no knowledge of the objects that ultimately cause our perceptions (for more on these sorts of arguments, see [Hatfield 1990, 165–71, 195–208, and esp. 208–218; Beiser 2014, 199–205, 381–86], and the entries on Hermann von Helmholtz, and Friedrich Lange). Thus, if Dühring rejects transcendental idealism, he simply has not consistently followed his own prescription that philosophy should base itself on the empirical sciences. And if Hartmann claims to know the nature of things in themselves, he can do so only by flagrantly ignoring the results of those sciences.