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Montesquieu and the separation of powers
1689–1755· Philosopher· Politics, society & justice
Well documentedSolid records, texts or physical evidence.
French judge and writer whose The Spirit of the Laws (1748) argued that liberty requires separating legislative, executive and judicial power.
See it on the Philosophy map →The idea
Idea: power must check power. Reasoning: when one person or body makes the laws, enforces them and judges cases, liberty is lost. Drawing on his reading of England's constitution, he set out three separate branches. He also argued that laws must fit a country's climate, size, religion and customs, an early sociology. His Persian Letters (1721) satirized France through foreign eyes. Main objection: he misdescribed England, where Parliament and the ministers overlapped heavily.
Why it matters
The US Constitution's three branches and checks and balances follow him; Madison's Federalist No. 47 calls him 'the oracle' on the subject.
Legacy and sources
The Spirit of the Laws, printed in Geneva in 1748 and put on the Catholic Index of banned books in 1751, survives with his notes; he visited England in 1729–31.
Still debated
His climate theory of national character is now rejected, and his ironic attack on slavery is read in conflicting ways.
Connections (2)
▸Montesquieu and the separation of powers shaped the political program of The EnlightenmentWell documented
The connection
Montesquieu gave the Enlightenment its main political design: liberty is protected by dividing power among legislative, executive and judicial branches that check one another. He also treated laws as products of social conditions, encouraging reformers to compare societies rather than rely on tradition or divine right.
When and how
The Spirit of the Laws, Geneva, 1748; translated into English in 1750 and widely read in Britain and America.
How we know
Madison's Federalist No. 47 (1788) calls him 'the oracle' on separation of powers; studies of American founding-era writings rank him among the most cited authors.
Debates and open questions
How far the US Constitution followed Montesquieu, rather than British practice and colonial experience, is debated.
▸John Locke influenced Montesquieu and the separation of powersWell documented
The connection
Locke distinguished legislative, executive and 'federative' (foreign affairs) powers and insisted that lawmaking power be limited. Montesquieu refined this into three branches, adding an independent judiciary, and shared Locke's goal of government that protects liberty, using the English system both men admired as the model.
When and how
Locke's Second Treatise (1689); Montesquieu's The Spirit of the Laws (1748), written after his stay in England, 1729–31.
How we know
Book 11, Chapter 6 of The Spirit of the Laws, on the English constitution, closely parallels Locke; Montesquieu seldom cites him, so the link is inferred.
Debates and open questions
Some historians argue English writers such as Bolingbroke, and Montesquieu's own observations, shaped him as much as Locke did.