The Enlightenment was a philosophical movement that lasted about one hundred years, neatly corresponding to most of the eighteenth century; convenient dates for it are from the Glorious Revolution in Britain to the beginning of the French Revolution: 1688 - 1789. The central concern of the Enlightenment was applying rational thought to almost every aspect of human existence: not just science, but philosophy, morality, and society. Along with those philosophical themes, central to the Enlightenment was the emergence of new forms of media and new ways in which people exchanged information, along with new “sensibilities” regarding what was proper and desirable in social conduct and politics.
We owe to the Enlightenment fundamental modern beliefs. Enlightenment thinkers embraced the idea that scientific progress was limitless. They argued that all citizens should be equal before the law. They claimed that the best forms of government were those with rational laws oriented to serve the public interest. In a major break from the past, they increasingly claimed that there was a real, physical universe that could be understood using the methods of science, in contrast to the false, made-up universe of “magic” suitable only for myths and storytelling. In short, Enlightenment thinkers proposed ideas that were novel at the time, but were eventually accepted by almost everyone in Europe (and many other places, not least the inhabitants of the colonies of the Americas).
The Enlightenment also introduced themes of thought that undermined traditional religious beliefs, at least in the long run. Perhaps the major theme of Enlightenment thought that ran contrary to almost every form of religious practice at the time was the rejection of “superstitions,” things that simply could not happen according to science (such a virgin giving birth to a child, or wine turning into blood during Communion). Most Enlightenment thinkers argued that the “real” natural universe was governed by natural laws, all watched over by a benevolent but completely remote “supreme being” - this was essentially the same as the Deism that had emerged from the Scientific Revolution. While few Enlightenment thinkers were outright atheists, almost all of them decried many church practices and what they perceived as the ignorance and injustice behind church (especially Catholic) laws.
The Enlightenment was also against “tyranny,” which meant the arbitrary rule of a monarch indifferent to the welfare of his or her subjects. Almost no Enlightenment thinkers openly rejected monarchy as a form of government - indeed, some Enlightenment thinkers befriended powerful kings and queens - but they roundly condemned cruelty and selfishness among individual monarchs. The perfect state was, in the eyes of most Enlightenment thinkers, one with an “enlightened” monarch at its head, presiding over a set of reasonable laws. Many Enlightenment thinkers thus looked to Great Britain, since 1689 ruled by a monarch who agreed to its written constitution and worked closely with an elected parliament, as the best extant model of enlightened rule.
Behind both the scientific worldview and the rejection of tyranny was a focus on the human mind’s capacity for reason. Reason is the mental faculty that takes sensory data and orders it into thoughts and ideas. The basic argument that underwrote the thought of the Enlightenment is that reason is universal and inherent to humans, and that if society could strip away the pernicious patterns of tradition, superstition, and ignorance, humankind would arrive naturally at a harmonious society. Thus, almost all of the major thinkers of the Enlightenment tried to get to the bottom of just that task: what is standing in the way of reason, and how can humanity become more reasonable?