Denis Casabianca

1It is a commonplace of critical literature to take up the question of the filiation of Descartes in the framework of a debate that seems to re-instantiate the opposition between “Cartesians” and “Newtonians” (see Postigliola, p. 93). The option chosen often depends on the reading that is done of the scientific “model” from which Montesquieu took inspiration to write L’Esprit des lois (see Géhin, 1973). If the question of borrowings from Descartes should indeed shed light on the degree of Montesquieu’s scientific culture, it must all the same observe that the “heritage” is not limited to this domain. The first difficulty then is to know whether the extent of the borrowings refers to a coherence of their utilization, so that Montesquieu could be said to possess a “Cartesian spirit”. The second difficulty is that what this term covers can be extremely hazy, so vast is the “Cartesian” nebula at the time when Montesquieu is writing (Beyer, p. 159-173). Rather than try to situate Montesquieu exteriorly in a Cartesian “current” by noting common themes, we will therefore attempt to examine the particular use he makes of the reference to Descartes so as to understand the unity of view that engages him to mobilize them.

2There is only one text in which Montesquieu defines himself as a Cartesian, and as he knows that the expression is equivocal, he takes care to specify that he is a “rigid” Cartesian as opposed to “mixed Cartesians who have abandoned their master’s rule” (Essai d’observations sur l’histoire naturelle, OC, t. VIII, p. 213). In the context of the study of the vegetable kingdom, one must be a strict physicist and seek to understand the production of plants on the basis of a mechanistic schema. The explanatory theses advanced are however not a strict repetition of Descartes’s. What is targeted by this remark is the mixture of genres; the criticisms against the research of Geoffroy and Andry also target the Malebranchian philosophy which inspires them. It is thus devout Cartesianism that is attacked and “Descartes’s grand system” (ibid.) is praised because it obliges the scientist to inquire into nature outside all theological investigation. In the Persian Letters, when Usbek praises “human reason” (LP, [‣]) to a Persian monk, it is again Descartes who appears as the figure of the philosopher trying to see through the chaos and understand the “order” of the universe. Montesquieu is exposing the mechanistic vision of nature, the universal and immutable character of its laws, and he takes the trouble to spell out the first laws of motion drawn from the Principles of philosophy. But we should note that in the same text, Montesquieu makes a list of scientific discoveries to manifest the fecundity of new research that also stems from a tradition of non-Cartesian observers. It is thus the alliance of reason and observation that Montesquieu puts forward to oppose the light of scientific discourse to the mysteries of religious discourse.

3The very movement of scientific research leads one to distance oneself from Descartes’s physical theses. That is why Montesquieu reproaches one author for “absolutely following Descartes’s system” (Discours sur la cause de la pesanteur des corps [‘Discourse on the cause of the gravitation of bodies’], 1719, OC, t. VIII, p. 231; italics added). He even elaborated in 1723 a Mémoire sur le principe et la nature du mouvement [‘Paper on the principle and nature of motion’], also known under the title Dissertation sur le mouvement relatif [‘Dissertation on relative movement’] which raises questions about the very principles of Descartes’s physics of motion (see the résumé given by Sarrau de Boynet and the edition of Alberto Postigliola, OC, t. VIII, p. 259-266). It thus appears that being a “rigid Cartesian” is not to follow Descartes word for word, blindly, but to take inspiration from him and follow his spirit. If Descartes’s physics, which misused geometry, is false, if his system is overturned, if others make new discoveries he was unable to make, it remains that it was he who opened the way, he is indeed the first of “those great philosophers” (Discours prononcé le 15 novembre 1717 à la rentrée de l’académie [de Bordeaux], ibid., p. 112). Thus in the Discours sur la cause de l’écho (1718), Montesquieu presents the author crowned by the academy as a new Descartes, who studies nature in its “simplicity” and holds on the “Ariadne’s thread” (ibid., p. 154-155). Descartes is the instigator of modern science, and it is in this sense that one must understand Newton as “Descartes’s successor” (Essai d’observations sur l’histoire naturelle, ibid., p. 223). He is even his true hero. How not to see his features under the figure of Hercules which Montesquieu invokes to describe the task of men of science (Discours prononcé à la rentrée de l’académie de Bordeaux, p. 110-111)? It is current practice in the 18th century to invoke Descartes to correct Descartes, and Montesquieu echoes it (Pensées, no. 775). Descartes himself would have insisted on these corrections. Montesquieu’s “critical Cartesianism” (Postigliola, p. 107) can in this sense be understood as an “authentic” or “rigid” Cartesianism. The liberation which Descartes permitted in his critique of authority must be pursued in the free examination of his philosophy. To detach oneself from him is to manifest one’s attachment for the freedom he permitted (Pensées, no. 1445).

4Descartes frees men from prejudices and superstitions. One text makes of him someone who could have prevented the colonization of the Indians: Descartes v. Cortez (Pensées, no. 1265, and Discours sur les motifs qui doivent nous encourager aux sciences, 1725, OC, t. VIII, p. 495). Montesquieu in fact makes use of a text of Descartes’s on the usefulness of philosophy (understood in its broad sense, the whole body of knowledge) and on the opposition between savage and civilized nations (Letter-preface to the French edition of the Principles of philosophy), which permits him to manifest a filiation and perform a displacement (Descartes in Mexico!). The struggle against prejudice is also called upon in a political and historical context. It is no longer a matter of a personal path aiming at the elaboration of certain knowledge as in Descartes: freeing a people from prejudice engages a collectivity, what is at stake is political (in the text the very existence of the Indian collectivity), and it is sciences that are the means of liberation. Montesquieu does not insist on Descartes’s revealing the world as it is: Descartes’s physics is false and sciences have always sought the truth. But by his way of seeing the world, he led us to see differently. It is not just a vision of the world that Descartes transmitted, it is a faculty he gives to use when one has considered how he used it himself (“But who would have given to the first the faculty to succeed?” [Mais qui est-ce qui aurait donné au premier la faculté d’arriver ?], Pensées, no. 1445; italics added).

5To renew Descartes is necessarily to surpass him, and use that faculty to see further, to continue to see the world with a new pair of eyes. The exercise of that faculty is not limited to the sciences: “Princes are so surrounded by the circle of their courtiers, who hide everything from them and make sure they see nothing, that he who came to see clearly would be like Descartes, who came out of the shadows of the old philosophy.” (“Les princes sont si fort environnés du cercle de leurs courtisans, qui leur dérobent tout et leur ôtent la vue de tout, que celui qui viendrait à voir clair serait comme Descartes, qui sortit des ténèbres de la vieille philosophie.”, Pensées, no. 1626). It is this very desire that animates the preface to L’Esprit des lois. The objective is to enlighten the people and those who command it, and to enquire into prejudices in their social dimension so as to exercise human reason in its legislative work. If Montesquieu is a man of the Enlightenment, it is first of all in this recognition he manifests for the one who was so attached to the “light of reason”.

6So it is not surprising to see Descartes called upon in the last part of the Défense de L’Esprit des lois to respond to the attacks of theologians (L’Esprit des lois, OC, t. VII, p. 113). The two-sided strategy of Descartes is its pivot: first the theologians must be sent back to their studies by reaffirming the separation that Descartes had made between what belongs to faith and what belongs to knowledge, between two languages which have fundamentally different discourses and meanings. Theology “has its formulas” (ibid., p. 112) and Montesquieu holds a different discourse for the reader. This is the second side of the strategy that seeks to show that neither of these positions is condemnable, and that the figure of Descartes intervenes at this moment: despite the accusations of atheism which he underwent, he is presented as a genuine defender of religion. One might suppose that the theologians were not fooled by this sort of argument. If Montesquieu is willing to correct certain formulations, he does not mean to bend under the criticisms; as a rigid Cartesian he will continue to speak “freely” (LP, [‣]). The rigidity mentioned in the Essai d’observations is therefore not circumstantial; it must be understood non only as a scientific rigor which Montesquieu owed to his master. It is a single attitude that is maintained from the Lettres persanes to L’Esprit des lois.


Charles Jacques Beyer, “Montesquieu et l’esprit cartésien”, Actes du congrès Montesquieu, Bordeaux: Delmas, 1956, p. 159-173.

Étienne Géhin, “Descartes et Montesquieu: de l’objectivité de la nature à l’idée de système politique”, Revue française de sociologie 14 (1973/2), p. 164-179.

Alberto Postigliola, “Montesquieu entre Descartes et Newton”, Montesquieu: les années de formation (1689-1720), , Cahiers Montesquieu 5 (1999), p. 91-108.

Denis de Casabianca, “Montesquieu, un ‘cartésien rigide’?”, dans Qu’est-ce qu’être cartésien ? Delphine Kolesnik (ed.), Lyon : ENS-Éditions,