Quote by Voltaire: “Doubt is not a pleasant condition, but certainty is an absurd one.”

Being uncertain is uncomfortable, but being absolutely sure of everything is far more dangerous. People who doubt keep questioning and learning. People who are certain stop. Voltaire saw unearned certainty — especially in religion and politics — as a source of tremendous human suffering.

Voltaire wrote to Frederick the Great of Prussia in 1767 in terms consistent with this sentiment, though the precise formulation appears in various letters of the 1760s. The Enlightenment was a period of fierce conflict between rational inquiry and religious authority across Europe.

French Enlightenment writer, historian, and philosopher famous for his wit, his attacks on religious intolerance, and his advocacy for freedom of speech. His satirical novella Candide, published in 1759, remains a masterpiece of ironic prose.