John Locke (1632-1704), the 17th-century Enlightenment philosopher, is often considered the father of classical liberalism. Locke’s ideas about liberty and his aversion to authoritarianism were reflected in the American Declaration of Independence. He was also a proponent of social contract theory, or the idea that the government forms a contract with the people it governs, and can only rule through the explicit consent of the governed.

Locke and the Birth of America

Trained in medicine and a supporter of empiricism (the notion that knowledge derives from experience), Locke was an important Enlightenment philosopher whose writings heavily influenced America’s founders, particularly "his political theory of government by the consent of the governed as a means to protect 'life, liberty and estate,'" according to History.com, and his views on religious tolerance, which laid the foundation for the separation of church and state codified in the Constitution. Specifically, Thomas Jefferson relied on Locke’s "Two Treatises on Government," which held that "when a king loses the consent of the governed, a society may remove him."