本文分析康德的自由理論，把它解釋為一種獨特的相容論。康德認為要解決自由與因果決定論的衝突，必須接受現象與物自身的區分。不少學者把這區分視為兩種不同的存有領域，然後在這基礎上討論康德的自由理論；但本文嘗試論證，把上述區分視為兩種理解或描述事物的方式，才能把握康德自由理論的精髓。本文亦將指出康德的自由概念不僅是其道德哲學，而是整個理論哲學的基礎，箇中關鍵是理解康德的「自發性」概念，視之為思想與認知能力的自由，這樣才能理解為何康德會聲稱，「自由」概念構成整個理性體系的拱頂石。

This paper analyzes Kant’s theory of freedom, interpreting it as a peculiar form of compatibilism. Kant maintains that the distinction between appearances and things in themselves is necessary for resolving the antinomy between freedom and causal determinism. Many scholars consider it a distinction between two different ontological realms and interpret Kant’s theory of freedom based on it. However, this paper aims to show that the key point of Kant’s theory can only come to light under the two-aspect interpretation. This paper argues that the concept of freedom is not only essential for Kant’s moral philosophy, but also indispensable for his theoretical philosophy. It is crucial to understand Kant’s concept of spontaneity, which means the freedom of thinking and cognition, in order to appreciate in what sense Kant claims that the concept of freedom constitutes the keystone of the whole system of pure reason.