Montesquieu is the most underrated thinker in the Western political tradition.

Not because he was obscure – The Spirit of the Laws sold out its first edition and went through twenty-two printings in 18 months. But because he was so completely absorbed into the foundations of Western constitutionalism that he became invisible – like load-bearing walls when the house is standing.

1. His central insight made America possible and France impossible: power must be separated. Different powers must belong to institutions with different interests, constituencies, and timescales, so no single force can accumulate enough authority to become tyrannical. In 1748, this was revolutionary. Every government that existed at that moment was, in some form, a concentration of power. Montesquieu looked at England — the only partial exception — and understood what France was missing.

2. He invented comparative political science. As a diagnostic tool: he asked not "what is the ideal government?" but "what kind of government produces what results, under what conditions?" This was Aristotle’s method applied to political systems: observe, compare, follow the evidence. The Spirit of the Laws is less a theory of how governments should be than an empirical study of how they actually work – and what their differences cost in human freedom.

3. The separation of legislative, executive, and judicial power was his most consequential contribution. Madison read Montesquieu closely; parts of the Federalist Papers are essentially Montesquieu translated into American. The Constitution’s architecture is his architecture. Every check, balance, veto, and independent court flows from one insight: the most reliable protection against the abuse of power is a system in which power constrains power. Not virtue. Not good intentions. Structure.

4. He understood that liberty is not the absence of government but the product of the right kind of government. This is the distinction the French Enlightenment repeatedly failed to make – and it helps explain why 1776 and 1789 produced such different results. Rousseau wanted a virtuous government. Montesquieu wanted a system in which government’s virtue was largely irrelevant because its structure constrained it regardless. One requires "philosopher-kings." The other requires architects. The architects won in Philadelphia. The philosopher-kings won in Paris. The results were not the same.

5. He understood that climate, geography, and culture constrain political possibility. Not all peoples are equally ready for all forms of government at all times. The institutions that produced English constitutionalism could not simply be transplanted onto a society with a different history and social fabric. You cannot design an ideal society from first principles and impose it on any population. The material matters. History matters. The accumulated habits of a people matter – and cannot be replaced by decree.

6. The French ignored him. France has a recurring habit of producing brilliant diagnoses and then abandoning them for the next beautiful abstraction. Montesquieu published in 1748. The Revolution came in 1789. The most precise available map of what produces freedom and tyranny sat largely unused by those who would soon build guillotines in the name of liberty. The Americans read Montesquieu. The French read Rousseau. The difference in outcomes requires little explanation.

7. He is present in every functioning constitutional democracy – and absent wherever power is concentrated in the name of efficiency, emergency, or "the greater good." The administrative state Tocqueville diagnosed, and which we increasingly inhabit, is the inversion of Montesquieu’s architecture: power concentrated, institutions captured, courts politicized, and executives expanding into every space legislatures vacate.

Montesquieu built the house.

The current tenants have been quietly removing the load-bearing walls.

They are surprised when the ceiling sags.