  Vaihinger’s first intervention in these foundational debates came in the form of his short tract Hartmann, Dühring, and Lange. Its title notwithstanding, the book is less a work of historical exegesis, and more a polemical defense of Lange’s Kantian standpoint against the dual assault of naïve realism (represented by the positivism of Eugen Dühring) and unchecked metaphysical speculation (exemplified by Hartmann’s Neo-Schopenhauerian view, according to which fundamental reality is a monistic vital substance). Vaihinger’s chief charge against Hartmann and Dühring is that they are dogmatists, that they systematically overstep the critical strictures Kant had placed on cognition, claiming knowledge of things in themselves (1876, 10, 17). Both commit “the original sin of post-Kantian philosophy”—Hegel’s “fantastic petitio principii” of “the unity of thought and being” (1876, 67). Lange’s Neo-Kantianism, by contrast, represents something like the best of both worlds, and so promises a middle path in a seemingly intractable dispute. With Dühring, Lange emphasizes the importance of grounding philosophy in the results of the empirical sciences. But with Hartmann, he avoids naïvely eliding the empirical objects studied by the sciences with things in themselves.