In 1751 the Roman Catholic Church added De l'esprit des lois to its Index Librorum Prohibitorum ("List of Prohibited Books").

This principle acts as a spring or motor to motivate behavior on the part of the citizens in ways that will tend to support that regime and make it function smoothly.

Montesquieu claims, for example, that the English failed to establish a republic after the Civil War (1642–1651) because the society lacked the requisite love of virtue.

"Political liberty" is Montesquieu's concept of what we might call today personal security, especially in so far as this is provided for through a system of dependable and moderate laws.

Generally speaking, establishing political liberty on a sound footing requires two things: This book mainly concerns explicit laws, but also pays considerable attention to cultural norms that may support the same goals.

"Montesquieu believed the hard architecture of political institutions might be enough to constrain overreaching power — that constitutional design was not unlike an engineering problem," as Levitsky and Ziblatt put it.

Later writers often caricatured Montesquieu's theory by suggesting that he claimed to explain legal variation simply by the distance of a community from the equator.