The Enlightenment, or Age of Enlightenment, rearranged politics and government in earthshaking ways. This cultural movement embraced several types of philosophies, or approaches to thinking and exploring the world. Generally, Enlightened thinkers thought objectively and without prejudice. Reasoning, rationalism, and empiricism were some of the schools of thought that composed the Enlightenment.
Experiencing empiricism: The "people" drive government
John Locke (1602 to 1704), an English medical doctor and philosopher, introduced empiricism in his 1689 Essay Concerning Human Understanding. He and his empiricist heirs — among them the Scotsman David Hume (1711 to 1776) — took the natural sciences as their model for all knowledge.
Locke's work was tremendously important to philosophy, but he had just as big an influence on political thought, especially with his idea that authority derives solely from the consent of the governed.
If you contrast that with older notions about the divine right of kings (which held to the belief that nobody except God — and sometimes the pope — should be able to tell a king what to do), you can see how Locke's idea led to political upheaval. Locke's work influenced the men who set the American Revolution in motion. Some French guys that you can read about in just a few paragraphs were on a similar wavelength.
Thomas Hobbes, political philosopher: The monarch rules
Not every philosophy rooted in scientific thinking seemed pointed toward popular revolt. Thomas Hobbes (1588 to 1679) was an Englishman who took an intellectual route from mathematics to political theory, a path that led him to advocate absolute monarchy.
The Oxford-educated, well-traveled Hobbes became interested, rather late in life, in why people allowed themselves to be ruled and in what would be the best government. In 1651, he wrote his famous work Leviathan. (Although the word means "sea monster" and sometimes refers to a whale, Hobbes applied it to the powerful state, or commonwealth.)
Hobbes argued that each person is self-interested and thus the people collectively cannot be trusted to govern society. Perhaps the most often quoted thing he wrote was a description of what human life was, or would be, without strong authority to keep everybody in line:
During the time men live without a common power to keep them all in awe, they are in that condition called war . . . as if of every man against every man. . . . The notions of right and wrong, justice and injustice have there no place. . . . No arts; no letters; no society; and which is worst of all, continual fear, and danger of violent death: and the life of man, solitary, poor, nasty, brutish, and short.
The "solitary, poor, nasty, brutish, and short" part drew much attention, especially "nasty, brutish, and short." (No, it's not a description of Hobbes.) A simple search for just those three words on the Internet turns up many references to the phrase. Among them, you'll find the English rock band that goes by the name of Nasty, Brutish, and Short.
For all his distrust of human nature, Hobbes was interested in justice and he did advocate that people band together so that the monarch would hear their concerns. He even coined the term "voice of the people."
Reasoning to rationalism: There's order in politics
Rationalism, another seventeenth-century philosophy, chose reason and logic, rather than observation (the senses) as the basis for knowledge.
Rationalism grew into a political movement, too, based in Paris and embodied in a group of writers including the poet Voltaire (1694 to 1798) and Swiss-born essayist Jean Jacques Rousseau (1712 to 1778).
Rationalism traces to René Descartes (1596 to 1650), the French mathematician who invented analytical, or Cartesian (for Decartes) geometry. (Cartesian geometry uses algebra to solve geometric problems, in case you were wondering who to blame for that.)
Descartes believed reason could be based on knowledge that just exists — independent of sense-experience. (Think of the way mathematical principals seem to exist on a plane separate from everyday reality.)
Descartes decided that the only thing beyond doubt was his own thinking. This resulted in one of the most memorable quotes in all philosophy: "I think, therefore I am."
Expanding to the Encyclopedists: Rising to revolution
In the 1770s, Voltaire and other leading thinkers, led by the critic Denis Diderot (1713 to 1784), published Encyclopèdie, a collection of social and political writing. Encyclopèdie used reason to attack France's old order, the ancien régime.
The Encyclopedists were intensely interested in the American Revolution, which broke out in the same decade that they were collaborating. The interest was mutual. Many of America's rebels were Enlightenment thinkers — especially Thomas Jefferson, who wrote the Declaration of Independence. Signed in 1776, it contained phrases such as "We hold these truths to be self-evident" (rationalism) and 'certain unalienable Rights" (which sounds inspired by Locke and Rousseau).
Jean Jacques Rousseau's works — especially his 1755 Discourse on the Origin and Foundations of Inequality Amongst Men, which emphasized the natural goodness of human beings, and 1762's The Social Contract — had a big influence on political thinking of the time. The Social Contract introduced the slogan, "Liberty, Equality, Fraternity," battle cry of the French Revolution in 1789.