The Short Answer
The Enlightenment was roughly 1685 to 1815, though nobody agrees on the exact dates. It's an intellectual movement, not a single event, so pinning it down precisely is always going to be a bit arbitrary. Most textbooks will tell you it spans the late 17th century through the end of the 18th century. The broad strokes are easy. The actual period is messier than that, which is the point I want to get into here. The conventional start date usually traces back to around 1685, with the publication of works by people like John Locke and the mathematical advances of Newton. The end is even less clear-cut. Some say it ends with the French Revolution in 1789. Others push it to about 1815, right after Waterloo, because the intellectual habits formed during that period kept running well past the political upheavals.
I've seen syllabi split the difference and call it 1715 to 1789, anchoring the start to Louis XIV's death and the end to the Revolution. That's defensible, but it's still a choice. There isn't one correct range. One thing beginners miss is that the Enlightenment wasn't a unified school of thought. It was a loose collection of thinkers across several countries who happened to share certain commitments — empirical reasoning, skepticism toward established authority, faith in progress — but disagreed with each other constantly. Voltaire and Rousseau, for example, deeply admired each other early on and then became fierce critics. That friction is part of what made the period productive. Another counter-intuitive detail: the Enlightenment wasn't primarily a French phenomenon, even though France is where the word "philosophe" comes from and where some of the most recognizable figures operated. The British Empiricists — Locke, Hume, Boyle — were doing completely different work from the French Encyclopedists, and they influenced each other only partially. Germany had its own parallel movement, often called the Aufklärung, with Kant and Mendelssohn, and the American founding generation drew selectively from both British and French sources without really being part of either camp.
I once ran into a problem grading papers where students would conflate the Scientific Revolution with the Enlightenment as if they were the same thing. The Scientific Revolution — roughly 1543 to 1687 — laid the methodological groundwork. The Enlightenment inherited those methods and applied them to society, politics, economics, and morality. The overlap is real but the projects are distinct. One is about how to understand the natural world. The other is about how to organize human life. Here's the practical takeaway if you're trying to use this timeframe for a paper or presentation: pick a range, justify it in a sentence or two, and move on. Don't get dragged into the endless debate about exact boundaries. The dates are tool, not truth. The Diderot Encyclopédie, published between 1751 and 1772, is probably the single best concrete reference point if you want something to hold onto. It's massive, it's messy, and it captures the period's ambition to compile all human knowledge under the banner of reason. Reading excerpts from it will give you a better sense of the era than any textbook summary.
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Also worth noting: the period had real blind spots. The same thinkers championing reason and liberty were frequently complicit in colonialism, slavery, or outright misogyny. Kant wrote elegant philosophy about autonomy while making deeply racist claims about non-European peoples. Voltaire's letters on colonialism are uncomfortably dismissive. This isn't a flaw in the historical record. It's just fact. Good scholars acknowledge it directly instead of pretending the Enlightenment was morally consistent. If you need a single working definition for a class or project, this should work: the Enlightenment was a transnational intellectual movement from roughly the late 1600s to the early 1800s that prioritized reason, empirical evidence, and critique of tradition as the primary tools for understanding and improving human society. It wasn't coherent. It was influential. Those are two different claims and both are true.
