Critik der practischen Vernunft

Immanuel Kant (1724–1804) spent his whole life in and around Königsberg in East Prussia, where he taught at the university for decades and kept such regular habits that, according to legend, neighbours set their clocks by his afternoon walk. He was fifty-seven when he published the Critique of Pure Reason, which changed philosophy.

Answering David Hume, who he said woke him from his dogmatic slumber, Kant asked what we can know, what we ought to do and what we may hope, and gave the world the categorical imperative and the motto of the Enlightenment, 'Dare to know'. His short essay Perpetual Peace is his most accessible work.