In 1690, Locke redefined subjectivity, or the concept of self, in his Essay Concerning Human Understanding. This idea influenced the development of psychology and all further Western thought about the value of individuals.
Locke’s writings opposed the absolute and arbitrary monarchy of his time. He believed that government, consistent with human nature, must be characterized by reason and tolerance. His ideals of representative government confronted the established English social order, and found appeal among American and French revolutionaries in the next century. Locke also advocated governmental separation of judicial, executive, and legislative powers.
One of the earliest advocates of the separation of church and state following the European wars of religion, Locke also evolved a classic rationale for religious tolerance by governments. He reasoned that a state lacks ability to evaluate the truth of competing religious standpoints; the state cannot violently enforce belief; and coercing a single state-sponsored religion would result in more social disorder than by permitting religious diversity. Locke echoed Rhode Island founder Roger Williams’s plea for absolute religious freedom and the total separation of church and state.
Constitutional monarchy and parliamentary democracy were in their earliest stages during Locke's time. His arguments concerning liberty and the social contract later influenced the written works of Alexander Hamilton, James Madison, Thomas Jefferson, and other Founding Fathers of the United States. A passage from his second Treatise of Government is reproduced verbatim in the Declaration of Independence (the reference to a ‘long train of abuses’). Most scholars also credit Locke’s theory of rights with the phrase ‘life, liberty, and the pursuit of happiness,’ in the American Declaration of Independence.
Today, many contemporary libertarians attribute the ideal of minimal government to Locke. He wrote, ‘The end of law is not to abolish or restrain, but to preserve and enlarge freedom,’ and government cannot ‘dispose of the estates of the subjects arbitrarily.’ Viewing individual consent as the basis of governmental legitimacy, he believed that revolution is not only a right but an obligation in some circumstances. Thomas Jefferson later concurred, stating, ‘The tree of liberty must from time to time be refreshed with the blood of patriots and tyrants.’