康德於《純粹理性批判》中〈先驗辯證論〉之宇宙論第三種二律背反亦即自然與自由之對立不但是康德哲思批判轉向之關鍵，也是其批判哲思發展之主軸。本文企圖對於該段文本進行即文本內在性亦系統內在性之詮釋。首先介紹該背反之思想脈絡亦即哲學宇宙論背反問題之源生，以及在此脈絡中自然與自由之命題背反底基本形式架構，亦即以波氏方陣所呈現者。接著進入正反命題亦即自由者與自然者之論證及其結果，亦即皆以所謂間接證明法進行。正命題之論證證立自由於思想向度之可能性，康德進一步設想所問先驗性的自由之概念。反命題則否證一切自由之可能而奠定決定論。然後康德再以其所謂先驗觀念論解消宇宙論理念背反，特別是其所謂現象與物自身之區分。本文在簡介先驗觀念論之精義脈絡下解析現象與物自身之區分如何解消自然與自由之背反。最後，吾人亦揭示此背反之解消，尤其是其自由概念在康德批判哲思本身中之發展，以及其對於德意志觀念論哲思生成之啟發。

The third Antinomy of the cosmological ideas in the “transcendental dialectic” in Critique of Pure Reason ? the contrast between nature and freedom ? is not only the key of the critical turn of Kant’s philosophizing, but also the centre of the development of his critical thinking. This essay tries to offer a text- and system-immanent Interpretation of the text from this theme. Firstly it shall introduce the conceptual context of the theme about antinomies, i.e. the genesis of the problematic of philosophical-cosmological antinomies, and the basic logical structure of the antinomy of nature and freedom on this context, i.e. the presentation of it in the square of Opposition. Then it shall come to the thesis and antithesis, their argumentations and their results, that is to say, the justification of their assertion through indirect proof (apagogischer Beweis). The argument of thesis justifies the possibility of thinking of freedom, so that Kant conceptualizes his idea of transcendental freedom. The argument of antithesis tries to falsify the possibility of freedom and therefore to ground the determinism of nature causality. And then Kant applies his transcendental idealism, especially the difference of Phenomena and Thing in itself as his dissolution-concept for the antinomy of nature and freedom. This essay would take a brief view about the core-meaning of the transcendental idealism and analyze how the distinction between appearances and things in themselves dissolves the antinomy between nature and freedom in this context. Finally it shall open the horizon of the development of this dissolution and Kant's idea of freedom in his critical philosophizing and the inspiration from them for the genesis of German idealism.