John Locke (August 29, 1632 – October 28, 1704) was a 17th century philosopher concerned primarily with society and epistemology. An Englishman, Locke's notions of a "government with the consent of the governed" and man's natural rights-life, liberty, and estate (property)-had an enormous influence on the development of political philosophy. His ideas formed the basis for the concepts used in American law and government, allowing the colonists to justify revolution. Locke's epistemology and philosophy of mind also had a great deal of significant influence well into the Enlightenment period. Locke has been placed in a group called the British Empiricists, which includes David Hume and George Berkeley. Locke is perhaps most often contrasted with Thomas Hobbes.
Locke's two main works, An Essay Concerning Human Understanding and Second Treatise on Civil Government were written more or less concurrently at the end of the seventeenth century.
In the Essay, Locke critiques the philosophy of innate ideas and builds a theory of the mind and knowledge that gives priority to the senses and experience. His adherence to this doctrine is what has led to him sometimes being called an empiricist rather than a rationalist such as his critic Leibniz, who wrote the New Essays on Human Understanding. Book II of the Essay sets out Locke's theory of ideas, including his distinction between passively acquired simple ideas, such as "red," "sweet," "round," etc., and actively built complex ideas, such as numbers, causes and effects, abstract ideas, ideas of substances, identity, and diversity. Locke also distinguishes between the truly existing primary qualities of bodies, like shape, motion and the arrangement of minute particles, and the secondary qualities that are "powers to produce various sensations in us" (Essay, II.viii.10) such as "red" and "sweet." These secondary qualities, Locke claims, are dependent on the primary qualities. In Chapter xxvii of book II Locke discusses personal identity, and the idea of a person. What he says here has shaped our thought and provoked debate ever since. Book III is concerned with language, and Book IV with knowledge, including intuition, mathematics, moral philosophy, natural philosophy ("science"), faith and opinion.
The Second Treatise on Civil Government were highly subversive texts when they were written, and Locke was for a long time reluctant to admit authorship of them. They have now become cornerstones to political liberalism.
Locke's work, particularly the concepts of liberty, later influenced the written works of Thomas Jefferson and other Founding Fathers of the United States. In particular, the Declaration of Independence drew upon many 18th century political ideas, derived from the works of both Locke and Montesquieu.