  In the Dialectic, Kant claims that certain concepts (e.g., those of an immaterial soul, freedom of the will, and God) have their root in pure reason. He argues that such concepts are mere “Ideas” (Ideen), in the sense that they are not constitutive principles of experience, and thus yield no “cognition” (Erkenntnis) of objects. Nevertheless, he suggests they are “not arbitrarily thought up” (A 327/B 384), but have a number of important “regulative” uses. In his works on moral philosophy, Kant goes on to argue that we can even have a certain kind of “practical cognition” of or “rational faith” in the Ideas. A natural interpretation of Kant’s position regarding the Ideas holds that we lack theoretical justification for believing that they refer to objects, and this lack of justification is such that we cannot claim knowledge of the existence or non-existence of such objects. Practical reason, however, may provide justification for the belief in (say) the existence of God, even if not of a sort sufficient to yield knowledge of him. Vaihinger disputes this reading. Instead, he interprets the Ideas as self-conscious fictions, which are nevertheless licensed by their theoretical and practical utility. This utility justifies us in “making use” of such concepts—looking, e.g., at nature as though it were the product of an intelligent designer—but never in believing they refer to objects. The interpretation relies crucially on two factors: first, a suggestive passage in which Kant calls Ideas “heuristic fictions” (A 771/B 799), and contrasts them with hypotheses; and second, Kant’s frequent use of ‘als ob’ and related locutions when describing the regulative employment of the Ideas. Both the distinction between fictions and hypotheses, and the idea of treating reality as if certain concepts appropriately applied to it are major themes that find extensive development in the PAO.