The English philosopher and political theorist John Locke (1632-1704) laid much of the groundwork for the Enlightenment and made central contributions to the development of liberalism. Trained in medicine, he was a key advocate of the empirical approaches of the Scientific Revolution. In his “Essay Concerning Human Understanding,” he advanced a theory of the self as a blank page, with knowledge and identity arising only from accumulated experience. His political theory of government by the consent of the governed as a means to protect “life, liberty and estate” deeply influenced the United States’ founding documents. His essays on religious tolerance provided an early model for the separation of church and state.