The Spirit of the Laws

A vast comparative study, in thirty-one books, of how laws relate to a people's government, climate, soil, religion, commerce and customs; Montesquieu worked on it for some twenty years. Laws, he argues, are not arbitrary but follow from the nature of things, and good laws suit the people for whom they are made. He divides governments into republics, monarchies and despotisms, each with its own principle: virtue for republics, honour for monarchies and fear for despotism. Book XI defines political liberty as security under law and, describing England, argues that it depends on keeping legislative, executive and judicial power apart. Books XIV to XVII link character and institutions to climate, a theory now largely set aside. Book XX argues that commerce softens manners and inclines nations to peace. Other books treat slavery, which he attacks partly through irony, as well as taxation, population, religion, and the history of Roman and feudal law.

Its account of the separation of powers fed directly into the American Constitution, and its comparative method is an early form of political sociology.