The essential idea of the Enlightenment was the belief in reason and the ability of reason to guide the way people were governed and the way people thought about the world around them. The ideas of the Enlightenment were far reaching and touched the fields of philosophy, government, science, art, medicine, and religion.
Many factors led to the Enlightenment and gave rise to its central belief in reason. Perhaps foremost among them was the scientific discoveries that Kepler, Galileo, and others made in the world of astronomy, and the formulation of the scientific method by Bacon. The scientific method relied on the idea that observations, rather than superstition or religion, helped guide the way scientific theories were made. In other words, people could not rely on superstition anymore and had to rely on their powers of observation and reason to make hypotheses about the natural world. In addition, the age of discovery exposed people to new worlds and ideas, making them question old precepts.
Enlightenment thinkers such as Locke, Montesquieu, and Voltaire dedicated themselves to understanding how reason governed the way people were ruled. Locke believed in the social contract, the idea that the governed had inalienable rights, rights that could not be taken away by their rulers. These ideas were diffused mainly through writing. For example, the Enlightenment figure Diderot wrote an encyclopedia in which he hoped to capture all knowledge. His multi-volume work helped disseminate knowledge.
The ideas of the Enlightenment inspired revolutionary change, and the ideology of the Enlightenment was one of the factors behind the French and the American Revolutions. The idea that people had certain rights that could not be taken away and that they had to be governed by reason rather than merely by tradition meant that people were no longer tolerant of monarchs who they felt had violated their inalienable rights. The idea of the divine right of kings--that monarchs had a God-given right to rule--was over. The Enlightenment inspired people to question the way they were ruled.