In 1784, a Prussian philosopher named Immanuel Kant published a short essay entitled What is Enlightenment? He was responding to nearly a century of philosophical, scientific, and technical advances in Central and Western Europe that, he felt, had culminated in his own lifetime in a more enlightened and just age. According to Kant, Enlightenment was all about the courage to think for one’s self, to question the accepted notions of any field of human knowledge rather than relying on a belief imposed by an outside authority. Likewise, he wrote, ideas were now exchanged between thinkers in a network of learning that itself provided a kind of intellectual momentum. Kant’s point was that, more than ever before, thinkers of various kinds were breaking new ground not only in using the scientific method to discover new things about the physical world, but in applying rational inquiry toward improving human life and the organization of human society. While Kant’s essay probably overstated the Utopian qualities of the thought of his era, he was right that it did correspond to a major shift in how educated Europeans thought about the world and the human place in it.

Following Kant, historians refer to the intellectual movement of the eighteenth century as the Enlightenment. Historians now tend to reject the idea that the Enlightenment was a single, self-conscious movement of thinkers, but they still (usually) accept that there were indeed innovative new themes of thought running through much of the philosophical, literary, and technical writing of the period. Likewise, new forms of media and new forums of discussion came of age in the eighteenth century, creating a larger and better-informed public than ever before in European history.

The Enlightenment was a 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?

One of the major causes of the Enlightenment was the Scientific Revolution. It cannot be overstated how important the work of scientists was to the thinkers of the Enlightenment, because works like Newton’s Mathematical Principles demonstrated the existence of eternal, immutable laws of nature (ones that may or may not have anything to do with God) that were completely rational and understandable by humans. Indeed, in many ways the Enlightenment begins with Newton’s publication of the Principles in 1687.

Having thus established that the universe was rational, one of the major themes of the Enlightenment was the search for equally immutable and equally rational laws that applied to everything else in nature, most importantly human nature. How do humans learn? How might government be designed to ensure the most felicitous environment for learning and prosperity? If humans are capable of reason, why do they deviate from reasonable behavior so frequently?

Among the other causes of the Enlightenment, perhaps the most important was the significant growth of the urban literate classes, most notably what was called in France the bourgeoisie: the mercantile middle class. Ever since the Renaissance era, elites increasingly acquired at least basic literacy, but by the eighteenth century even artisans and petty merchants in the cities of Central and Western Europe sent their children (especially boys) to schools for at least a few years. There was a real reading public by the eighteenth century that eagerly embraced the new ideas of the Enlightenment and provided a book market for both the official, copyrighted works of Enlightenment philosophy and pirated, illegal ones. That same reading public also eagerly embraced the quintessential new form of fiction of the eighteenth century: the novel, with the reading of novels becoming a major leisure activity of the period.

Thus, the Enlightenment thought took place in the midst of what historians call the “growth of the public sphere.” Newspapers, periodicals, and cheap books became very common during the eighteenth century, which in turn helped the ongoing growth of literacy rates. Simultaneously, there was a full-scale shift away from the sacred languages to the vernaculars (i.e. from Latin to English, Spanish, French, etc.)., which in turn helped to start the spread of the modern state-sponsored vernaculars as spoken languages in regions far from royal capitals. For the first time, large numbers of people acquired at least a basic knowledge of the official language of their state rather than using only their local dialect. Those official languages allowed the transmission of ideas across entire kingdoms. For example, by the time the French Revolution began in the late 1780s, an entire generation of men and women was capable of expressing shared ideas about justice and politics in the official French tongue.

There were various social forums and spaces in which groups of self-styled “enlightened” men and women gathered to discuss the new ideas of the movement. The most significant of these were coffee houses in England and salons in France and Central Europe. Coffee houses, unlike their present-day analogs, charged an entry fee but then provided unlimited coffee to their patrons. Those patrons were from various social classes, and would gather together to discuss the latest ideas and read the periodicals provided by the coffee house (all while becoming increasingly caffeinated). Salons, which were common in the major cities of France and Germany, were more aristocratic gatherings in which major philosophers themselves would often read from their latest works, with the assembled group then engaging in debate and discussion. Salons were noteworthy for being led by women in most cases; aristocratic, educated women were thought to be the best moderators of learned discussion by most Enlightenment thinkers, men and women alike.

One of the best-known salons, run by Marie Thérèse Rodet Geoffrin, seated on the right. All of the men pictured are their actual likeness. Two are of particular note: seated under the marble bust is Jean le Rond D’Alembert, noted below, and the bust is of Voltaire (also described below), whose work is being read to the gathering in the picture.

Outside of the gatherings at coffee houses and salons, the ideas and themes of the Enlightenment reached much of the reading public through the easy availability of cheap print, and it is also clear that even regular artisans were conversant in many Enlightenment ideas (to cite a single example, one French glassworker, Jacques-Louis Menetra, left a memoir in which he demonstrated his own command of the ideas of the period and even claimed to have chatted over drinks with the great Enlightenment philosopher Jean-Jacques Rousseau). The major thinkers of the Enlightenment considered themselves to be part of a “republic of letters,” similar to the “republic of science” that played such a role in the Scientific Revolution. They wrote voluminous correspondence and often sent one another unpublished manuscripts. Thus, from the thinkers themselves participating in the republic of letters down to artisans trading pirated copies of enlightenment works, the new ideas of the period permeated much of European society.