The Enlightenment has been defined in many different ways, but at its broadest was a philosophical, intellectual and cultural movement of the seventeenth and eighteenth centuries. It stressed reason, logic, criticism, and freedom of thought over dogma, blind faith, and superstition. Logic wasn't a new invention, having been used by the ancient Greeks, but it was now included in a worldview which argued that empirical observation and the examination of human life could reveal the truth behind human society and self, as well as the universe. All were deemed to be rational and understandable. The Enlightenment held that there could be a science of man and that the history of mankind was one of progress, which could be continued with the right thinking.
Consequently, the Enlightenment also argued that human life and character could be improved through the use of education and reason. The mechanistic universe - that is to say, the universe when considered to be a functioning machine - could also be altered. The Enlightenment thus brought interested thinkers into direct conflict with the political and religious establishment; these thinkers have even been described as intellectual “terrorists” against the norm. They challenged religion with the scientific method, often instead favoring deism. The Enlightenment thinkers wanted to do more than understand, they wanted to change for, as they believed, the better: they thought reason and science would improve lives.
When Was the Enlightenment?
There is no definitive starting or ending point for the Enlightenment, which leads many works to simply say it was a seventeenth and eighteenth-century phenomena. Certainly, the key era was the second half of the seventeenth century and almost all of the eighteenth. When historians have given dates, the English Civil wars and revolutions are sometimes given as the start, as they influenced Thomas Hobbes and one of the Enlightenment's (and indeed Europe's) key political works, Leviathan. Hobbes felt that the old political system had contributed to the bloody civil wars and searched for a new one, based on the rationality of scientific inquiry.
The end is usually given as either the death of Voltaire, one of the key Enlightenment figures, or the start of the French Revolution. This is often claimed to have marked the downfall of the Enlightenment, as attempts to rework Europe into a more logical and egalitarian system collapsed into bloodshed which killed leading writers. It's possible to say that we are still in the Enlightenment, as we still have many of the benefits of their development, but I've also seen it said we're in a post-Enlightenment age. These dates do not, in themselves, constitute a value judgment.
Variations and Self-Consciousness
One problem in defining the Enlightenment is that there was a great deal of divergence in the leading thinkers' views, and it is important to recognize that they argued and debated with each other over the correct ways to think and proceed. Enlightenment views also varied geographically, with thinkers in different countries going in slightly different ways. For instance, the search for a “science of man” led some thinkers to search for the physiology of a body without a soul, while others searched for answers to how humanity thought. Still, others tried to map humanity's development from a primitive state, and others still looked at the economics and politics behind social interaction.
This might have led to some historians wishing to drop the label Enlightenment were it not for the fact that the Enlightenment thinkers actually called their era one of Enlightenment. The thinkers believed that they were intellectually better off than many of their peers, who were still in a superstitious darkness, and they wished to literally 'lighten' them and their views. Kant's key essay of the era, “Was ist Aufklärung” literally means “What is Enlightenment?”, and was one of a number of responses to a journal which had been trying to pin down a definition. Variations in thought are still seen as part of the general movement.
Who Was Enlightened?
The spearhead of the Enlightenment was a body of well-connected writers and thinkers from across Europe and North America who became known as the philosophes, which is the French for philosophers. These leading thinkers formulated, spread and debated the Enlightenment in works including, arguably the dominant text of the period, the Encyclopédie.
Where historians once believed that the philosophes were the sole carriers of Enlightenment thought, they now generally accept that they were merely the vocal tip of a much more widespread intellectual awakening among the middle and upper classes, turning them into a new social force. These were professionals such as lawyers and administrators, office holders, higher clergy and landed aristocracy, and it was these who read the many volumes of Enlightenment writing, including the Encyclopédie and soaked up their thinking.
Origins of the Enlightenment
The scientific revolution of the seventeenth century shattered old systems of thinking and allowed new ones to emerge. The teachings of the church and Bible, as well as the works of classical antiquity so beloved of the Renaissance, were suddenly found lacking when dealing with scientific developments. It became both necessary and possible for philosophes (Enlightenment thinkers) to begin applying the new scientific methods - where empirical observation was first applied to the physical universe - to the study of humanity itself to create a “science of man”.
There was not a total break, as the Enlightenment thinkers still owed a lot to Renaissance humanists, but they believed they were undergoing a radical change from past thought. Historian Roy Porter has argued that what in effect happened during the Enlightenment was that the overarching Christian myths were replaced by new scientific ones. There is a lot to be said for this conclusion, and an examination of how science is being used by commentators does seem to greatly support it, although that's a highly controversial conclusion.
Politics and Religion
In general, Enlightenment thinkers argued for freedom of thought, religion, and politics. The philosophes were largely critical of Europe's absolutist rulers, especially of the French government, but there was little consistency: Voltaire, critic of the French crown, spent some time at the court of Frederick II of Prussia, while Diderot traveled to Russia to work with Catherine the Great; both left disillusioned. Rousseau has attracted criticism, especially since World War 2, for appearing to call for authoritarian rule. On the other hand, liberty was widely espoused by Enlightenment thinkers, who were also largely against nationalism and more in favor of international and cosmopolitan thinking.
The philosophes were deeply critical, indeed even openly hostile, to the organized religions of Europe, especially the Catholic Church whose priests, pope, and practices came in for severe criticism. The philosophes were not, with perhaps some exceptions like Voltaire at the end of his life, atheists, for many still believed in a god behind the mechanisms of the universe, but they railed against the perceived excesses and constraints of a church they attacked for using magic and superstition. Few Enlightenment thinkers attacked personal piety and many believed religion performed useful services. Indeed some, like Rousseau, were deeply religious, and others, like Locke, worked out a new form of rational Christianity; others became deists. It was not religion which irked them, but the forms and corruption of those religions.
Effects of the Enlightenment
The Enlightenment affected many areas of human existence, including politics; perhaps the most famous examples of the latter are the US Declaration of Independence and the French Declaration of the Rights of Man and the Citizen. Parts of the French Revolution are often attributed to the Enlightenment, either as recognition or as a way to attack the philosophes by pointing to violence such as the Terror as something they unwittingly unleashed. There is also debate about whether the Enlightenment actually transformed popular society to match it, or whether it was itself transformed by society. The Enlightenment era saw a general turn away from the dominance of the church and the supernatural, with a reduction in belief in the occult, literal interpretations of the Bible and the emergence of a largely secular public culture, and a secular “intelligentsia” able to challenge the previously dominant clergy.
The Enlightenment of the seventeenth and eighteenth centuries era was followed by that of a reaction, Romanticism, a turn back to the emotional instead of the rational, and a counter-Enlightenment. For a while, in the nineteenth century, it was common for the Enlightenment to be attacked as the liberal work of utopian fantasists, with critics pointing out there were plenty of good things about humanity not based on reason. Enlightenment thought was also attacked for not criticizing the emerging capitalist systems. There is now a growing trend to arguing that the results of the Enlightenment are still with us, in science, politics and increasingly in western views of religion, and that we are still in an Enlightenment, or heavily influenced post-Enlightenment, age. More on the effects of the Enlightenment. There has been a lean away from calling anything progress when it comes to history, but you'll find the Enlightenment easily attracts people willing to call it a great step forward.