Denis Casabianca

1In the Essai d’observations sur l’histoire naturelle, Montesquieu meant to study the production of plants as a physicist. According to him, to speak of plants “as a philosopher” is to assert that “the best organized plant is a simple and easy effect of the general movement of matter” (OC, t. VIII, p. 207). The physicist would examine only the movements of matter to understand its effects. The idea of organization (Pensées, no. 76), which was to be the master word of La Mettrie, for example, and the image of the perpetual motion of all things, can lead one to think that the scientific approach here gives way to a more philosophical materialism, to a metaphysical position. The question of how Montesquieu conceived material reality and what powers he recognized in it leads us to wonder about his relation to Descartes. Indeed in the Essai d’observations the position he defends is that of a “rigid Cartesian” as opposed to “those who allow a particular providence of God in the production of plants” (“ceux qui admettent une providence particulière de Dieu dans la production des plantes”, OC, t. VIII, p. 213). From rigid Cartesianism to exaggerated Cartesianism (to “Spinozism”) is a short step which it is imprudent to take too overtly. Must we think that in these questions Montesquieu advances masked? The accusations of Spinozism to which he must answer after the publication of L’Esprit des lois are in part aroused by the evocation of a “blind fatality” and the presentation of the world “formed by the movement of matter” (“formé par le mouvement de la matière”, EL, I, 1).

2We must first note that research concerning matter was inscribed in a Cartesian framework (LP, [‣]). But, as the Discours sur la cause de la pesanteur des corps [‘Discourse on the cause of the weight of bodies’] (May 1720) and the Discours sur la transparence des corps [‘Discourse on the transparency of bodies’] (August 1720) attest, his Cartesianism is always a “critical” one (Postigliola, p. 107). Montesquieu does not take up the physical theses of Descartes, he even opposes them, as the Dissertation sur le mouvement relatif [‘Discourse on relative motion’] of 1723 attests (see the summary given by Sarrau de Boynet, OC, t. VIII, p. 261-266). A letter from Dodart (28 December 1723) which comments on this lost paper enables us to specify the nature of the opposition. Montesquieu’s central thesis is that motion is essential to matter (Bianchi, p. 120). It is no longer conceived as a transposition in space but as an internal activity of bodies, an essential property, which is opposed to the Principles of philosophy (II, 25). An important consequence of this thesis is that there is no absolute repose (see also Pensées, no. 136). This does not only mean that motion is always relative, which might be the case for Descartes (Principles, II, 24), but that all matter tends to move and cannot remain in repose. Imagining that God were to abolish motion, it would start up again on its own. This is opposed to continuous creation and to the idea of force in Descartes (Principles, II, 43; letter to Morus, August 1649, Charles Adam and Paul Tannery ed., t. V, 1903, p. 402-405). Indeed, for Descartes, no body possesses an inner force, but the force of each is only that of God which persists. That is what makes motion continue unless some other body intervenes to impede it (Principles, II, 39). Physics, for Descartes, ought to determine the laws of motion and the exterior causes (other bodies) of changes; the idea of force or a first cause (that initiates motion) belongs to metaphysics. To allow as Montesquieu does that motion can be “caused” by matter itself is to raise questions about the metaphysical foundations of physics. That is why the theses developed in these texts of 1723 seem close to materialist positions. Without being able to speak of influence, we can for example compare the ideas of moving matter with Gassendi’s materia actuosa. He considered that the activity of the atom, or its own motion, cannot be taken away, even if it is stopped by another body. Similar ideas recur in the letter from Dodart minus the reference to atoms. We again find similar theses in an anonymous Lettre sur l’activité de la matière dated (coincidence?) 30 January 1723, though filiation cannot be established with certainty (Ehrard, p. 102).

3These comparisons do not however oblige us to conclude that Montesquieu was a “materialist” in the sense that this term could have in the 18th century. First for a “physicist” reason: Montesquieu was not an atomist. It is remarkable that we find in him no attention given to the composition of matter, no attempt to approach the elementary either in an atomic sense, or in a chemical sense: no decomposition into particles (the mechanical approach to aggregates), no composition of the elements (chemical approach to admixtures). Matter for Montesquieu seems to be a structure, an ensemble of relations. It is less about analyzing matter in itself than perceiving the relations that order it. If he posits motion as essential to matter, that is because the idea is only to understand these motions playing within it. From Descartes, Montesquieu retains the vortices, not the elements. In the understanding of the living, he adopts a fibrillary and not the atomist schema: now the fiber, a contractile tube, is not an “elementary”, it is only the relational form that allows inquiry into the play of motions in the living body (see on this site the article “Natural history”).

4One cannot dismiss the difficult text in which Montesquieu reports “objections which can be made by atheists” (Pensées, no. 1096, p. 392-394; see Casabianca). The “properties of matter” which he enumerates are not all ones he takes up himself (notably the property of “thinking”), even if it is true that we find passages in the Essai d’observations that echo them. The common themes must not obscure radical divergences. The fact that Montesquieu traces the genesis of materialist ideas (Pensées, no. 1946) lets us think that he was trying to point out the error in the formation of that representation. In the same text, he recalls that “before M. Descartes, philosophy had no proofs of the immateriality of the soul” (ibid.). Yet he does not subscribe to a metaphysical dualism. The rejection of “fatality” (in L’Esprit des lois) as that of “providence” (in Essai d’observations) are meant to relieve the physicist of all metaphysical shackles, by dismissing both theologians and materialists at the same time. The disaffection for the question of the status of the soul opens the possibility of a history of sensitivity where the physical observations can be present. Freed from metaphysical interrogation, physiological studies make it possible to inquire into the arousing of sensitivity and the formation of taste (Spector) in the play of the machine without at the same time reducing them to material movements.


Jean Ehrard, L’Idée de nature en France dans la première moitié du XVIIIe siècle (1963), Paris: Albin Michel, 1994.

Lorenzo Bianchi “Montesquieu naturaliste”, Montesquieu: les années de formation (1689-1720), ed. Catherine Volpilhac-Auger, Cahiers Montesquieu 5, 1999, p. 109-124.

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

Céline Spector, “Une théorie matérialiste du goût peut-elle produire l’évaluation esthétique? Montesquieu, de L’Esprit des lois à l’Essai sur le goût”, Corpus 40 (2002), p. 167-213 [].

Denis de Casabianca, “Des objections sans réponses? À propos de la ‘tentation’ matérialiste de Montesquieu dans les Pensées”, Revue Montesquieu 7 (2003-2004),