Doubt and Certainty in the Age of Enlightenment

Have you ever wondered how we know what we know about the world around us? Does our perception of reality correspond to something outside of our mind, or maybe everything we see around us is merely an illusion? Have you every questioned your own existence or inquired into the nature of your identity?

Enlightenment thinkers tried to articulate answers to these and many other puzzling questions. The late seventeenth and early eighteenth century was an exciting time for inquisitive minds. We often think of the Enlightenment as an “Age of Reason,” but this period in European history was actually overrun with doubts and uncertainties. It was an age of intellectual flux and dynamism. No question was off the table, and everything was up for debate.

Eighteenth-century philosophers were preoccupied with defining the powers and limits of the human mind. They questioned whether people could know anything with certainty—from the nature of colors, to the reality of the external world, and even to the existence of the self. Many writers of this period tried to distinguish between matters that could be productively debated and questions that were simply beyond the reach of human understanding.

In college courses, we are usually taught that René Descartes, the so-called father of modern philosophy, established the basic grounds for indubitable certainty and overthrew the yoke of medieval Aristotelian scholasticism in the mid-seventeenth century. Although Descartes’s challenge to the Aristotelian system aimed at establishing a new solid and indubitable philosophical foundation of human knowledge, it actually unsettled a relatively stable European learned culture and led to a crisis of certainty. By breaking the virtual monopoly that Aristotelian philosophy held over European higher education, Descartes and his followers opened the floodgates of philosophical uncertainty. Descartes’s disciples and other inventors of new metaphysical systems began to compete for intellectual primacy among a rapidly expanding reading public, proposing novel explanations of how the surrounding world functioned.

Late seventeenth and early eighteenth-century intellectuals intensely argued about the structure of the universe, the composition of matter, the relationship between mind and body, and, most significantly, about the methods that allowed them to answer those questions with confidence. These heated debates often led thinkers to doubt everything they had believed to be true and certain. Philosophical skepticism—an ancient Greek school of philosophy—proved particularly appealing for those who felt that the available philosophical explanations were all somewhat inadequate. Skepticism was thus a troubling specter that loomed over the learned world of the early Enlightenment and forced intellectuals to formulate new criteria of doubt and certainty in almost all areas of human knowledge.

This book explores how Enlightenment thinkers grappled with this crisis of philosophical confidence and tried to define what it meant to be certain, reasonable, and rational. It shows how the debates between the skeptics and their opponents led to the formation of new rules for understanding the world around us, and it sheds light on the origin of our modern notions of common sense, reasonableness, and probability.

Anton M. Matytsin is an assistant professor of history at Kenyon College. He is that author of The Specter of Skepticism in the Age of Enlightenment.