Charles, Baron de Montesquieu, born on January 18th 1689, was one of history’s most influential political thinkers. He never needed to earn his living, having inherited the fortune and the title of his uncle, but instead devoted his life to thinking and writing. Born a year after England’s “Glorious Revolution” had deposed the autocratic King James II and replaced him with a constitutional monarch, William III, he was influenced by, and admired, the way the English had introduced institutions that tempered absolutism. He compared this unfavourably with the unchecked power of the French monarchy.
His 1748 book, “The Spirit of the Laws,” set out the notion of the separation of powers, a principle that underlies the US constitution, and which has been incorporated into the constitutions of many other countries. He proposed that the three branches of government, the executive that directs the country, the legislature that makes its laws, and the judiciary that adjudicates its justice, should be separate and independent of each other.
This went beyond the English constitution, which had the executive embedded within the legislature by virtue of its ability to command a majority, and until recent times had the judiciary within the legislature’s upper chamber. Montesquieu’s idea was that the separation of the three branches, in tension with each other, would limit the power of the state, and therefore enlarge the liberties of its subjects.
His book was banned by the Catholic Church, but was widely acclaimed in Britain, and especially among the American colonists. His innovation was the recognition that rulers had to be restrained by checks and balances. Since Plato, people had supposed that power could be checked if leaders were virtuous and acted with restraint. Montesquieu disagreed. Morality does not check power. Only power checks power. And if each source of power is checked by others, it will be restrained. That insight was Montesquieu’s lasting contribution.