  The distinction between hypotheses and fictions is important for understanding Vaihinger’s revised brand of Kantianism in another way as well. In the Dialectic, Kant had argued that dogmatic metaphysics necessarily leads reason into a series of conflicts, or “antinomies,” with itself. It can produce, that is, equally valid arguments putatively establishing both that freedom exists and that freedom does not exist, that matter is composed of simples and that matter is not composed of simples, and so on. Kant claims that these conflicts are “natural” to reason, since reason has an innate drive to know the “unconditioned.” He argues, however, that these conflicts can be avoided if (and only if) one recognizes the non-spatiotemporality of things in themselves. Transcendental idealism allows us to maintain that in some of the antinomial conflicts it is possible for both the thesis and antithesis to be false without contradiction, and that in others it is possible for both to be true without contradiction. The critical philosophy thus has the distinct advantage of being able to explain how certain apparently insoluble metaphysical debates arise, and of providing the only possible resolution of those debates. Vaihinger similarly posits a natural human tendency to confuse, not appearances and things in themselves, but fictions and hypotheses. Many statements that are introduced into our discourse as fictions end up being taken for hypotheses. And vice versa, many propositions that are originally intended as hypotheses are retained with mere fictional significance. Vaihinger calls this the “law of ideational shifts” (Gesetz der Ideenverschiebung) (PAO 92–99). Seemingly intractable debates in the sciences can be resolved, he maintains, by systematically recognizing this distinction. Thus, for instance, certain arguments against atomism are cogent if intended to establish that atomism is false (since it is contradictory); but they are erroneous if intended to imply that atomism should be rejected. Likewise, arguments for atomism are sure to fail if they are meant to establish the existence of atoms; but they are perfectly acceptable if they only aim to show that atomistic discourse is useful and indeed essential for scientific practice. For, the atomist’s discourse is best understood as a conscious fiction. As Vaihinger suggests, the confusion arises from ignoring the essential practical dimension of thought (PAO xviii).