John Locke (b. 1632, d. 1704) was a British philosopher, Oxford academic and medical researcher, whose association with Anthony Ashley Cooper (later the First Earl of Shaftesbury) led him to become successively a government official charged with collecting information about trade and colonies, economic writer, opposition political activist, and finally a revolutionary whose cause ultimately triumphed in the Glorious Revolution of 1688. Much of Locke's work is characterized by opposition to authoritarianism. This opposition is both on the level of the individual person and on the level of institutions such as government and church. For the individual, Locke wants each of us to use reason to search after truth rather than simply accept the opinion of authorities or be subject to superstition. He wants us to proportion assent to propositions to the evidence for them. On the level of institutions it becomes important to distinguish the legitimate from the illegitimate functions of institutions and to make the corresponding distinction for the uses of force by these institutions. The positive side of Locke's anti-authoritarianism is that he believes that using reason to try to grasp the truth, and determining the legitimate functions of institutions will optimize human flourishing for the individual and society both in respect to its material and spiritual welfare. This in turn, amounts to following natural law and the fulfillment of the divine purpose for humanity.

(Source: http://plato.stanford.edu/entries/locke/)

 
 
The Second Treatise of Government places sovereignty into the hands of the people. Locke's fundamental argument is that people are equal and invested with natural rights in a state of nature in which they live free from outside rule. In the state of nature, natural law governs behavior, and each person has license to execute that law against someone who wrongs them by infringing on their rights. People take what they need from the earth, but hoard just enough to cover their needs. Eventually, people begin to trade their excess goods with each other, until they develop a common currency for barter, or money. Money eliminates limits on the amount of property they can obtain (unlike food, money does not spoil), and they begin to gather estates around themselves and their families.

People then exchange some of their natural rights to enter into society with other people, and be protected by common laws and a common executive power to enforce the laws. People need executive power to protect their property and defend their liberty. The civil state is beholden to the people, and has power over the people only insofar as it exists to protect and preserve their welfare. Locke describes a state with a separate judicial, legislative, and executive branch--the legislative branch being the most important of the three, since it determines the laws that govern civil society.

People have the right to dissolve their government, if that government ceases to work solely in their best interest. The government has no sovereignty of its own--it exists to serve the people.

To sum up, Locke's model consists of a civil state, built upon the natural rights common to a people who need and welcome an executive power to protect their property and liberties; the government exists for the people's benefit and can be replaced or overthrown if it ceases to function toward that primary end.

(Source: http://www.sparknotes.com/philosophy/locke/summary.html)