Immanuel Kant's Critique of Pure Reason was first published in 1781.
Written in German as Kritik der reinen Vernunft, the book examined what human reason can know independently of experience and where metaphysical speculation reaches its limits. Kant published it in Riga through the printer Johann Friedrich Hartknoch. The first edition is often identified as the A edition.
Readers sometimes confuse 1781 with 1787, the year of Kant's substantially revised second edition. The later B edition reorganized and rewrote important passages, especially sections dealing with self-consciousness and the relation between perception and understanding, but it was not the work's first publication.
The Critique responded partly to the tension between rationalist philosophy and David Hume's skepticism about causation. Kant argued that the mind actively structures experience through forms such as space and time and concepts such as causality. The book became a landmark in modern philosophy and helped launch German idealism.