The Enlightenment, which is also referred to as the Age of Reason (or alternately as the Age of Rationalism), was a period when European philosophers emphasized the use of reason as the best method for learning the truth. Beginning in the 1600s and lasting through the 1700s, philosophers such as Jean-Jacques Rousseau (1712–1778), Voltaire (1694–1778), and John Locke (1632–1704) explored issues in education, law, and politics. They published their thoughts, issuing attacks on social injustice, religious superstition, and ignorance. Their ideas fanned the fires of the American and French revolutions in the late 1700s.

Hallmarks of the Age of Reason include the idea of the universal truth (two plus two always equals four, for example); the belief that nature is vast and complex but well ordered; the belief that humankind possesses the ability to understand the universe; the philosophy of Deism, which holds that God created the world and then left it alone; and the concept of the rational will, which posits that humans make their own choices and plans, and therefore, do not have a fate thrust upon them.

While the Age of Reason proved to be a flurry of intellectual activity that resulted in the publication of several encyclopedias of knowledge, toward the end of the eighteenth century a shift occurred. During this time Europeans began to value passion over reason, giving rise to the romantic movement and ending the Age of Reason. (This change in outlook is evident in English novelist Jane Austen’s Sense and Sensibility.)

Nevertheless, the philosophies put forth during the Age of Reason were critical to the development of Western thought. The celebration of individual reason during this era was perhaps best expressed by René Descartes (1596–1650), who refused to believe anything unless it could be proved. His statement, “I think, therefore I am,” sums up the feelings of skeptical and rational inquiry that characterized intellectual thought during the era.