Descartes Vs Montesquieu

Like Descartes, Montesquieu associated freedom as being in accordance with reason. Unlike Descartes, Montesquieu did discuss external freedom as embodied through law more at length, and also wrote extensively on the subject of slavery. In The Spirit of Laws, Montesquieu writes that “… political liberty does not consist in an unlimited freedom. In governments, that is, in societies directed by laws, liberty can consist only in the power of doing what we ought to will, and in not being constrained to do what we ought” (11.3). If the law is rational, then following the law is that which best promotes freedom precisely because it is in accordance with rationality. However, this begs the question of what is meant by rational law and whether living
Controversially, Louis Sala-Molins is critical of the idea that Montesquieu was fully condemning the practice of slavery in The Spirit of Laws. He argues that, in fact, “Contrary to received wisdom, Book XV of The Spirit of Laws does not provide a condemnation of slavery in general but only critiques the abuses of a practice that should be regulated but not eliminated.” What gives Sala-Molins this impression? In “Regulations Necessary in Respect to Slavery,” Montesquieu states that “But of whatsoever kind the slavery be, the civil laws should endeavor on the one hand to abolish the abuses of it, and on the other to guard against its dangers” (15.10). Later, in “Precautions to be Used in Moderate Governments,” he argues that:
Lenity and humane treatment may prevent the dangers to be apprehended from the multitude of slaves in a moderate government. Men grow reconciled to everything, and even to servitude, if not aggravated by the severity of the master. The Athenians treated their slaves with great lenity; and this secured that state from the commotions raised by the slaves among the austere Lacedæmonians.