Reason Must Be Our Last Judge

From Book IV, Chapter 19 of An Essay Concerning Human Understanding (1690), in Locke's chapter "Of Enthusiasm." John Locke was reacting against the religious enthusiasm of the Civil War period, when claims of divine inspiration overrode rational argument. His insistence that reason must be the final arbiter — not scripture, not tradition, not private revelation — was a landmark statement of Enlightenment rationalism. Immanuel Kant would later express the same principle as the motto of the Enlightenment: Sapere aude ("Dare to know").