Charles de Secondat, Baron de Montesquieu (January 18, 1689 - February 10, 1755) was a French political thinker who lived during the Enlightenment and articulated the theory of separation of powers, implemented in many constitutions the world over.
Born in 1689 at Chateau La Brede near Bordeaux, he was president of the parlement of Bordeaux by the age of twenty-seven, and shortly afterwards achieved literary success with the publication of his Lettres persanes (1721), a satire based on the imaginary correspondence of an Oriental visitor to Paris, pointing out the absurdities of contemporary society. He travelled widely, spending two years in England (1729 - 1731), but was troubled by poor eyesight, and was completely blind by the time of his death in 1755. His great work, De l'esprit des lois (Spirit of the Laws) (1748), was published anonymously and was enormously influential.
He argued that the aristocracy - which Voltaire would decry - protected the state from the absolutist despot (or monarchy) and from the despotism of the many (or anarchy). His was a purely political and rational defense, conveniently non-economic. Montesquieu's motto was, "Liberty is the stepchild of privilege." This allowed Montesquieu to defend the constitutional monarch as he claimed it was governed by honor. Montesquieu argued that the monarchs could become too passionate and the commons were too big and too egalitarian to rule properly. However, he portrayed the aristocracy as having and maintaining the honor that kept monarchies constitutional. But, he also warned that the aristocracy is doomed when it becomes self-interested, arrogant and parasitic.
Montesquieu's most radical work situated the three French classes into checks and balances, a term he coined, of three sovereignties; the monarchy, the aristocracy, and the commons. Montesquieu saw two types of powers existing; the sovereign and the administrative. The administrative powers were the legislative, the executive, and the judiciary. These powers were to be divided up amongst the three classes so that each would have a power over the other. This is so radical because it completely eliminates the clergy from the estates and because it erases any last vestige of a feudalistic structure.
Montesquieu's thought was a powerful influence on many of the American Founders, most notably James Madison.
We should also note that Montesquieu (like many of America's Founders) endorsed the practice of slavery (which was then very widespread in the French Empire) and held the view that people of African descent did not deserve to be treated as humans, writing: "Sugar would be too expensive if it were not produced by slaves. These slaves are blacks ... it is not possible that God, who is a very wise being, would have put a soul ... in such an utterly black body."