Natural History

Denis Casabianca

1The Essai d’observations sur l’histoire naturelle (‘Essay of observations on natural history’, read on 20 November 1721) has a particular status with respect to other “youthful” texts that Montesquieu wrote on scientific questions. It is not a discourse reporting to the Académie de Bordeaux on the different competing dissertations. If the research was conducted in the framework of the academy, then these are observations made by Montesquieu himself. In it he also defends a particular thesis on the formation of plants and a general mechanistic approach to natural phenomena: the work is polemical. It is Montesquieu’s best constructed and longest scientific text (450 lines in the Œuvres complètes). Before examining the content of his theses about living things, we must inquire about the meaning given to the expression “natural history”, which will allow us to specify the viewpoint that Montesquieu intended to bring to bear on natural reality.

2The title which Montesquieu chose is not anodyne: indeed inquiring into the sense of “natural history” leads one to examine the statute he accords to “observations” in scientific research. In science Montesquieu distinguishes observation from the construction of systems: “Observations are the history of physics, and systems are its fable” (“Les observations sont l’histoire de la physique, et les systèmes en sont la fable”, Pensées, no. 163). Should we see in this distinction a reminiscence of the apologue of the ants and spiders in Bacon (Novum organum, I, 95)? This distinction in Montesquieu is not designed to disqualify World-makers, like Descartes, to the benefit of attentive, meticulous observers like Réaumur, whom the role of the ant perfectly suits. Montesquieu praises, for example, the work of Bonnet on plants because he leads the reader “from observation to observation” (letter of 20 February 1754, Masson, t. III, p. 1496), but he also praises the systems of Descartes and Newton. Observations and systems play a role in research: “he who is unable to make a system like Newton, will make an observation with which he will put that great philosopher to the torture” (“celui qui ne saura pas faire un système comme Newton, fera une observation avec laquelle il mettra à la torture ce grand philosophe”, Essai d’observations sur l’histoire naturelle, OC, t. VIII, p. 223). The spirit of system, which derives in a certain way from the geometric spirit (see Casabianca, 2008, p. 290-295), leads one to forget to confront the real which offers itself for view in its diversity and history. Observations are never ended since the earth constantly changes its appearances: “The earth changes so much every day that it will endlessly give occupation to physicists and observers” (“La terre change si fort tous les jours qu’elle donnera sans cesse de l’emploi aux physiciens et observateurs”, Pensées, no. 102). From this point of view, Montesquieu renews the Baconian requirement of fidelity to phenomena: he places himself in this current which opposes to fascination with systems, to the pre-eminence of mathematics in the order of knowledge, the requirement to observe and relate what one has experienced. Observations report the facts that belong to the category of history in the study of nature (physics in the broad sense). History is the repertory of facts to explain; Montesquieu hails back to the first meaning of historia as inquiry and collection of facts. It thus signifies that observations alone are capable of furnishing facts which are collected in history; in a certain way they are the foundation of physics because the systematic activity that then puts these facts into order and examines them, is part of the fable (or story): it is secondary and bears the mark of the weaknesses of the human mind.

3In this presentation, the study of nature (physics) is indeed essentially natural history. This does not go without saying: Descartes for example had rejected history from the new rationality more geometrico, just as Hobbes had. D’Alembert, in the presentation of the sciences in the Preliminary Discourse of the Encyclopédie, does not speak of natural history, but designates by the term general physics the un-mathematized knowledge of nature which is “properly but a reasoned collection of experiments and observations” (“n’est proprement qu’un recueil raisonné d’expériences et d’observations”). Now that is just what Montesquieu seems to have been doing when he wrote his Essai d’observations sur l’histoire naturelle. Voltaire, in the article “History” for the Encyclopédie, criticizes the Baconian distinction and proposes that the expression natural history, which entails certain confusions, be eliminated: it is “improperly called history” since it is but an “essential part of physics”. Montesquieu’s argumentation would be strictly the reverse: this application is appropriate since the study of nature rests on observed facts that are carried over to other studies. This affirmation shows that Montesquieu opts, here against Descartes, for an empiricism that grants history a different status from the mere compilation of facts. The renewal of observations engages research and, in the dynamic conception of science which is his, this requirement must be understood as an invitation to know. For Fontenelle, the causal explanation and the formulation of laws belong to the domain of physics, whereas natural history should be limited to describing. The organization of the Académie des Sciences reflected this division of labor. Although physics and natural history etymologically designate the same thing, one in Greek, the other in Latin, the former searches for causes, the latter describes facts: manifestly, Montesquieu does not make this distinction. If he speaks rather of natural history than of physics in his title, that is also because that expression traditionally designates since the 16th century that which concerns the study of the earth, minerals, plants and animals. But the thesis he is defending is clear: he means to address plants as a “philosopher”, in other words as a “physicist”, by postulating that “the best-organized plant is but a simple and easy movement of matter” (Essai d’observations, OC, t. VIII, p. 207).

4The expression natural history as we find it in Montesquieu therefore does not have the exact same meaning that it was to be given in the second half of the century. The idea of a general and particular natural history that leads one to think about the “eras of nature” (époques de la nature) is foreign to him. Besides, the research in the Essai d’observations is more a study of vegetal physiology (physics of plants) than a detailed description of plants or an attempt at classification. If he indeed examines an insect at the beginning of Essai d’observations, his attitude is not that of a Réaumur who writes “particular histories” (histoires particulières). Despite the importance that Montesquieu gives to observations, he remains a “rigid Cartesian” (Essai d’observations, OC, t. VIII, p. 213). His position, in this early 18th century, is original insofar as it seems to foreshadow essential themes that would be developed in natural history, but it allies itself with a physicist’s approach in which the new naturalist approach cannot be fully deployed.

5Montesquieu is “between two” eras. He develops a mechanistic physiology that is characteristic of thinkers on life phenomena following Descartes. His research approaches an attitude more medical than naturalistic, as it appears in L’Esprit des lois, where the description of the play of the machine in function of changes of temperature features organic exchanges and climatic variations (EL, XIV, 2). In the Essai d’observations Montesquieu is interested in the formation of living beings and their functioning. Yet these physiological questions, which are raised also for a “naturalist” like Buffon, do not furnish the framework of the research. On the contrary, it is inscribed as a tool, essentially for the study of reproduction, in an inquiry that is no longer physiological. It is notable that the essential occupation of the “observer”, who works at describing minutely and classifying, is absent from Montesquieu’s work. He reveals a casualness that would exasperate Réaumur. The Essai d’observations begins with the study of an insect; but we know nothing about the specimen: “Having observed under the microscope an insect the name of which we do not know (perhaps it does not even have one, and is confused with innumerable others which we do not know) […]” (“Ayant observé dans le microscope un insecte dont nous ne savons pas le nom (peut-être même qu’il n’en a pas, et qu’il est confondu avec une infinité d’autres qu’on ne connoît pas) […]”, Essai d’observations, p. 195). The parenthesis is moreover perhaps ironically intended for the entomologist. Montesquieu does not “classify”. He elaborates no “system” of living things, whatever form that order might take, since he is not trying to extract an overall design of nature nor even a sketch on one (a term that is found among thinkers as diverse as Bonnet and Buffon).

6But at the same time, Montesquieu projects a look that opens the way to natural history. In the Projet d’une histoire de la terre ancienne et moderne (‘Project for a history of the ancient and modern world’, OC, t. VIII, p. 183-184), the term history also takes on a temporal dimension. The call sent out by Montesquieu insists on the attention that scientists must bring to bear on changes of all kinds. It is of course about a history in the traditional sense of an inquiry resting on observations (the text insists on the publicity of observations and the necessary verification of what is being examined) which remains in the framework of physics (but we have seen that Montesquieu did not oppose these two terms): attention to natural processes, however, inquires about nature in its modifications which are often imperceptible (Pensées, no. 90). At the same time, we observe that Montesquieu freed himself from a certain number of epistemological constraints that weigh on the work of observers like Réaumur. The Biblical story of the creation in six days and the Flood, which implies creationism and fixism, is not the framework for his investigations (a quotation from Genesis is treated ironically [Pensées, no. 1174]; Montesquieu’s opinion is “that there were very few species at the beginning, and they subsequently multiplied” [Pensées, no. 2014]; very clear reservations are expressed on Réaumur’s catastrophism [Pensées, no. 1481]). Nor do we find the common notion of the great chain of being that prefigures divine order. Bonnet’s reading of the first chapter of L’Esprit des lois in his Contemplation de la nature is very much in line with his project for a science that accords with religion, but it is a misinterpretation of the text. Finally, at the end of Essai d’observations (p. 219-222), Montesquieu explicitly opposes anthropocentrism and its corollary, utilitarianism, according to which God created plants and animals and all have their utility, even it if remains hidden. Against providentialism, he pleads for a development of human capacities for adapting to circumstances. In this sense he maintains a utilitarianism, since botany remains dependent on medical and agronomic aims, but he frees himself from the burden of ecclesiastical science. Montesquieu remains a “physicist” against an “observer” like Réaumur, his “history” remains physical and does not inquire of nature according to the categories of the naturalist such as he appears at the beginning of the 18th century. But this quite “Cartesian” reservation is paradoxically what unties him from the epistemological constraints that weigh on researchers, and what makes him seem to foreshadow the naturalist approach of a Buffon, even though the scientific frameworks he uses are different. This “anticipatory” reservation appears in Montesquieu’s own theses on living things: he intends to maintain a rigid mechanism that places him in the line of Descartes and leads him to criticize preformation at the very moment when the great majority of scientists are in agreement on this paradigm for thinking about reproduction. A retrospective view could lead one to compare certain points of this critique and the epigenesis that Montesquieu develops beginning with the thought of Buffon, though the context and the nature of the interrogation are completely renewed by the latter.

7Chapter 2 of book XIV of L’Esprit des lois lets us see the structure of our machine and how it moves. It enters both into a description of the machine order and a history of sensitivity, since the object of the chapter is to show how men feel differently in various climates. The understanding of this “sensitive creature” comes via an examination of the physical being of man (EL, I, 1). The text first insists on the characteristics of fibers, which enables one to clarify the relation of the machine to its milieu, and the inner order of the machine itself. For fiber is both the surface of man and his insides: it knits all of man’s matter. Which explains that the matter of man can be seen in the “tissue” (‘knit’) of the sheep’s tongue. Fiber’s first characteristic is its contractibility, which determines its quality: when tight, the fiber has more “spring”; relaxed, it has less strength and resilience (EL, XIV, 2). The attention to fibers manifests the desire to pursue the mechanistic study of living phenomena while recognizing the insurmountable difficulties which Descartes’s mechanism encountered. Representation of the body as being constituted of fibers derives from the microscopic observations that were multiplying at the end of the 17th century and theoretical efforts to conceive the order of the machine beginning with its microstructures. We find in Baglivi an original conception of the living fiber which might have been Montesquieu’s inspiration. It indeed seems that Montesquieu also thought of the fiber as an elementary form: the fiber contracts, hardens, lengthens, bends, prolongs itself by weaving itself. Its malleability makes of it the form that can take on all other forms, by its transformation it thus can compose all the body’s organs (Spicilège, no. 27). The body as a whole is thus but a fabric in which everything is connected, since each fiber attaches or prolongs itself in another fiber (for example, Spicilège, no. 679). If the fiber can change form that is because its structure allows it: the fiber is a tube. This representation accords with the mechanistic microstructuralist approach which tries to account for the properties of a body by a description of the structures and their transformations. The texture of the fiber makes it modifiable. As the fibers are hollow, the variations in their length and resilience make them more or less filled, and the liquid they contain is more or less under pressure. The theory of fibers is inseparable from a dynamics of fluids, as can be seen in the presentation Montesquieu makes in the book on climate. So it is not surprising to find in these texts a hydraulic model as among the iatrophysicists. The liquid is pressed, deflected, carried along by these contractile channels at the same time that it presses, dilates or empties these canals. Thus the movement of fluids is guided and communicated to all parts of the body. There is a mutual causality between the play of fibers and the movement of fluids (EL, XIV, 2) that should make it possible to account for the phenomena of autoregulation that characterize the living body, but also the disruptions that can occur. This schema appears distinctly in a reproduced text which deals with the contraction of the muscles and their strength (Spicilège, no. 105).

8It remains to be seen according to what principles Montesquieu conceived the integration of these microstructures. There again, the approach is strictly mechanical: the problem is to understand “the mechanics of the body (Essai sur les causes qui peuvent influer sur les esprits et les caractères, OC, t. IX, p. 238), to see how the “organic parts” are disposed (p. 237). It is this organization that is characteristic of the living and which needs to be brought to light (Pensées, no. 76). In no text is allusion made to a spiritual principle, a soul, a natural faculty to account for the specificity of the living. Since everything is tubes (or fibers, or vessels, or canals) and all the tubes are filled with liquids in motion, the organization of living bodies must be apprehended on the bases of two theses which refer back to each other: in a living body, everything is empty (Spicilège, no. 501) and everything is full (Pensées, no. 1239). Everything must be empty in order for everything to be filled, and vice versa. The whole of the living body must be understood as the knitting of an ensemble of fibers that is penetrated by the ensemble of fluids in motion, it is a dynamic knit. It is remarkable that this theory of the fiber, which manifests the microstructuralist and iatromechanistic influence, does not suppose, in Montesquieu’s text, an analytic approach to the living. Understanding the functioning of the body does not depend on an atomistic representation of the living. Montesquieu presupposes an economical physiology in which everything is in relation to everything. In this sense, the fiber serves as a paradigm: it is the primary microstructure. It is not, however, elementary in the sense that it would suffice to decompose the body into its elements to understand its structure. The fiber cannot be on the level of the living what the atom might be for inert matter because it cannot be isolated. By dint of its structure (a tube), it supposes a connection to other fibers. The fiber is primary because it is in relation and the relation is primary. The fibers are the ensemble of relations that constitute the organic being, the tubes are only the knitting that takes place among them; they are the circuits that make everything in the body connected. While defending a mechanistic approach, Montesquieu maintains a relational approach to the living, which allows him to articulate theses of Cartesian inspiration to a Hippocratic eye that supposes a principle of totality. That is also why his physiological research, despite the mechanism, does not engage him towards a materialistic reductionism. The question of generation concentrates the difficulties with regard to the living (Pensées, no. 16). At the beginning of the 18th century, the situation seems however to clarify itself, or at least to stabilize around the theory of the preformation of seeds. Yet it was to oppose this thesis that Montesquieu wrote his Essai d’observations. He speaks of the “mystery” of generation when he examines the difficulties of animalculism. He carefully notes observations, but his reservation concerning the “worm opinion” doubtless is owing to the fact that it supposes the preformation of germs; in certain texts the two theses are distinctly associated; and the arguments which Montesquieu uses refer to difficulties encountered by the thesis of preformation (Spicilège, no. 105; Pensées, nos. 16 and 1174). The examination of Geoffroy’s work, which was a medical and worldly event in 1704, manifests this opposition more clearly still (Spicilège, no. 105): the text which he reproduces confronts the thesis with descriptions, as if to oppose the system of preformation and history, the fable of creation and the observations that make natural history. The last observation weakens the idea of a containment of seeds maintained by the defenders of preformation; the allusion to Malebranche’s tulip (De la recherche de la vérité, book I, chap. VI, § 1) is transparent; the question then is to explain that his thesis is affirmed against observation. To be sure Geoffroy was not an ovist like Malebranche, but he was an author of reference. The praise of the Creator shows the theological framework that blinds the observer. In many places the text recopied by Montesquieu mimics that of Bougeant (Observations curieuses sur toutes les parties de la physique, Paris, 1719; Catalogue, no. [‣]) which is intended to confirm Geoffroy’s theses by new observations. The explanations of these scientists are put to the test. Montesquieu’s Essay, even in its title, takes a position opposed to those observers who contemplate the admirable order of Creation, without really trying to look at nature in a way that might be able to write its history.

9On these complex questions everything is thus played out in blades of grass. If the vegetal domain since Malpighi is a terrain of predilection for approaching living things as a body, it is also the source of Malebranche’s inspiration on preformation; the adversary needs to be dislodged on his own terrain. Such seem indeed to be the principal stakes in the Essai d’observations sur l’histoire naturelle: the observations on mistletoe, mosses and the willow branch are not only the most developed, but it is particularly with respect to them that Montesquieu draws general conclusions about the order of nature and situates his research in contemporary debates. It is concerning mosses that the thesis of preformation is clearly named and becomes the object of detailed refutation. The text brings in the hypothesis on seeds: it is the beginning hypothesis to which Montesquieu subscribes or pretends to subscribe and which would be put to the test of observation (Essai d’observations, p. 202-203; see also Spicilège, no. 247). Preformation indeed supposes that all plants come from seeds, since it is in seeds that the contained seeds are contained and develop, and unfold when the plant grows. Now the object of observing the mistletoe, as of mosses, was to show that there are plants that do without seeds. To complement this critique, Montesquieu evokes, as polemical facts, the phenomena of cuttings or regeneration. The stakes then seem double in this passage; the idea is indeed to invalidate preformation, but also to show how fiber representation opposes the seed theses. Having a clear notion of the fiber theory is important since Montesquieu was next going to develop a mechanistic explanation of vegetation on the basis of the notion of the fiber.

10He was seeking to establish a model of mechanical epigenesis of a general character on the basis of the examination of the particular case of the willow branch. The idea was to show what this “simple operation” can be for the production of plants, beginning with movements of matter. Montesquieu displaces the meaning of the “mystery” of generation in such a way as to restart scientific research: we pass from a theological unknown to a scientific unknown. The question then is how these fibers are formed, how they grow, how a fabric develops with nothing being enveloped. For the fiber is hollow, in itself it does not contain all these subsequent developments (it is not a seed) which are “fortuitous”. The overall idea is that it is the movement of the fluids that moves the fibers and makes them grow. The juices contained in the fibers coagulate in contact with air and reform a conduit by stretching. It is on the basis of this movement of the juices and the resistances they encounter that a circuit is formed that will make it possible to assure the development of the plant. This text, which goes against the majority theses accepted by the scientific community, manifests a resistance. Its conclusion claims the Cartesian filiation in polemical fashion. By distinguishing the “rigid Cartesians” to whom he belongs, and the “mitigated Cartesians” (Essai d’observations, p. 213), he intends to assert that mechanism and science have suffered a detrimental blow with the theory of preformation. With it theological discourse comes in, deflecting scientists from their research and blinding observers. Though the text of the Essai d’observations sur l’histoire naturelle does not explain everything, it stands as an example of the attitude which the researcher must adopt in the face of natural reality.


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

Essai sur les causes qui peuvent influer sur les esprits et les caractères, OC, t. IX, 2006, p. 203-269 (ed. Guillaume Barrera).

Essai d’observations sur l’histoire naturelle, OC, t. VIII, 2003, p. 185-223 (ed. Lorenzo Bianchi).

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

Denis de Casabianca, Montesquieu : de l’étude des sciences à l’esprit des lois, Paris: Champion, 2008.

Denis de Casabianca, “Le bon usage de ‘notre demeure’ : le regard de Montesquieu sur ‘les ouvrages des hommes’ dans la nature”, Dix-Huitième Siècle 45 (2013),