Summary

Henry E. Allison argues that Kant’s theoretical and practical philosophy are unified by a shared commitment to the spontaneity of rational agency, which he terms the “reciprocity thesis.” The book contends that Kant’s idealism is not a metaphysical doctrine about mind-dependent reality but a critical framework for understanding the conditions of experience and moral action. Allison defends this reading through detailed analyses of key Kantian texts, including the *Critique of Pure Reason* and the *Groundwork of the Metaphysics of Morals*, showing how concepts like the transcendental deduction, the categorical imperative, and the fact of reason cohere. Readers gain a rigorous interpretation of Kant’s system as a whole, emphasizing that freedom is not merely a postulate but a necessary presupposition of both cognition and morality.

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Key concepts

Reciprocity thesis — The claim that freedom and the moral law are mutually implicating, so that awareness of the moral law is the ratio cognoscendi of freedom.
Transcendental idealism — The view that space and time are forms of intuition, not properties of things in themselves, which Allison defends as a “methodological” rather than metaphysical doctrine.
Fact of reason — Kant’s notion that the moral law is given as an undeniable fact of rational consciousness, grounding the reality of freedom.
Spontaneity — The capacity of the understanding to produce representations independently of sensory input, central to both theoretical cognition and practical agency.
Incorporation thesis — The idea that inclinations only determine the will if they are taken up into a maxim through an act of spontaneity.
Categorical imperative — The supreme principle of morality, expressed as the formula of universal law, which Allison analyzes as a test for the consistency of maxims.