Montesquieu is the French philosopher best known for advocating the separation of powers in government. His political theory called for legislative, executive, and judicial powers to be distributed so that no single authority could dominate the state.
Montesquieu developed this argument most influentially in The Spirit of the Laws, published in 1748. He believed liberty was better protected when governmental powers were distinct and capable of limiting one another. His discussion drew partly on his interpretation of the English constitution, though modern systems of checks and balances do not reproduce his model exactly.
Earlier thinkers had discussed different forms of political authority, and Rousseau, Voltaire, and Diderot also contributed to Enlightenment political debate. They did not, however, make the separation of legislative, executive, and judicial powers the defining feature of their political philosophy in the way Montesquieu did.
Montesquieu’s ideas strongly influenced later constitutional design, especially in the United States and other countries. His full name was Charles-Louis de Secondat, Baron de La Brède et de Montesquieu, but “Montesquieu” is the standard name used in history and political theory.