To understand why rational thinkers, according to Kant, are naturally led to accept the Supreme Principle as true, we must answer two questions: why does the Logical Maxim have to become a principle of pure reason – that is, why is it rationally necessary to make regulative use of the Supreme Principle? And why does this lead to the illusion that the Supreme Principle is an objectively valid constitutive principle (i.e., a true descriptive statement about everything there is)? Chapter 5 offers answers to these questions. The latter question in particular requires a discussion of Kant’s account of transcendental illusion and the role of transcendental realism in bringing about this kind of illusion. The central idea is that transcendental realism implies that there is a correspondence between reason and reality; therefore, a tacit commitment to transcendental realism can explain why regulative principles of reason will naturally be taken to be constitutive principles that are true descriptions of reality itself. Even though transcendental realism is a weighty metaphysical claim, it can plausibly be attributed to common sense or ‘universal human reason.’ The chapter closes with a discussion of why, according to Kant, the Supreme Principle is valid for things in themselves.

Chapter 7 turns to the first two of the three metaphysical disciplines whose inferences and conclusions Kant discusses in the Transcendental Dialectic, namely, rational psychology and cosmology. We show how the four transcendental paralogisms and the arguments underlying the four antinomies of pure reason can be read as ‘necessary inferences of reason’ and how they result in the corresponding transcendental ideas. The chapter considers the paralogisms and the psychological ideas, discusses the role of transcendental realism in the paralogisms, looks at the derivation of the cosmological ideas and the four antinomies, and reconstructs the role of transcendental realism in the antinomies. In doing so, we concentrate on those aspects that are relevant to understanding how Kant develops his Rational Sources Account in the Transcendental Dialectic.

The Introduction explains the two major aims of the book. First, the book will offer a novel interpretation of the Transcendental Dialectic that isolates its constructive side, Kant’s account of the rational sources of speculative metaphysics (concerning the soul, the world as a whole, and God), and distinguishes it clearly from its destructive side, Kant’s critique of this kind of metaphysics. Second, it will reconstruct, and where possible defend, a Kantian account of the rational sources of metaphysical thinking. In particular, it will argue that Kant is right in claiming that metaphysical speculation arises naturally out of principles that guide us in everyday rational thought. As the book will argue, Kant gives us good reason to think that discursivity, iteration, and striving for completeness are fundamental features of rational thinking and that, taken together, they give rise to a specific kind of metaphysical speculation. This is a distinctive and original perspective on metaphysics that deserves to be taken seriously in the current metaphysical and meta-metaphysical debates.