1 A Successful Preface
In the Discourse on the Method, there is something of everything Descartes had written or was yet to write. The First Part, autobiographical, probably connects to the lost Studium bonae mentis; the Second Part, dedicated to method, and the Fifth Part, concerning issues of physics, return to themes already addressed in the Regulae and in The World; the Third Part announces the moral themes of the later years, which culminate in the Passions of the Soul; the Fourth Part connects back to the lost metaphysical treatise of 1629 and anticipates the future Meditations, while the Sixth Part expresses the ambition to propose a new paradigm of knowledge that will be realized in the Principles of Philosophy. There is thus the cogito ergo sum [je pense, donc je suis], there are the rules for reaching truth through self-evidence, there is the fable of the world, the demonstration of the existence of God founded on that of the thinking subject, the theory of animals as unconscious machines, the anatomical description of certain organs of the human body; there is, finally, the German Stube and the time at La Flèche. But it is a revised and corrected Descartes, who offers, for many of his principal doctrines, a toned-down version for undemanding readers, and moreover in French, so that everyone, “even women”,1 will be able to follow him some way.
A writing conceived as a simple “preface” or as a brief “warning” to the reader2 gradually overwhelmed and finally suppressed the three scientific essays it was supposed simply to introduce, and which follow it in the original 1637 edition: the Dioptrics, the Meteors, and the Geometry. That is the paradox of the Discourse on the Method, which, after a modest beginning (very few copies of the first edition were sold),3 would go on to enjoy an extraordinary and unfailing success, especially from the nineteenth century onwards. But among the hundreds of modern editions of the text, translated and reprinted in all the major languages of the planet, those which also contain the scientific works
On the other hand, if Descartes finally decided to publish something, it was above all to extract from his research some important results that had long been ready: he was already discussing some of the topics treated in the Dioptrics and Meteors in the autumn of 1629;5 as for the Geometry, although materially drafted at the last moment,6 it finally brings to fruition the long labour of unification of algebra and geometry begun way back in 1619.
The idea of a Discourse on the Method emerged only at the end of 1635.7 For the writing intended to introduce his scientific essays, Descartes imagined a long and grandiloquent title, vaguely reminiscent of his youthful reflections on mathesis universalis. Thus: The Project of a Universal Science, That Can Elevate Our Nature to Its Highest Degree of Perfection. Plus the Dioptrics, the Meteors, and the Geometry, in which the most curious subjects that the Author has been able to choose to demonstrate the universal science he proposes are explained in such a way that even those who have not studied may understand them.8 In the end, he fell back on the more modest – but not yet concise – Discourse on the Method of rightly conducting one’s reason and seeking the truth in the sciences and in addition the Optics, the Meteors and the Geometry, which are essays in this Method – to emphasize that he did not intend to write a dogmatic treatise but only to present certain aspects of his procedures of inquiry. The method, indeed, can neither be taught nor learnt from anyone, nor even studied, but
On 2 December 1636, Descartes signed with the bookseller Jan Maire of Leiden the publishing contract for the Discourse and the three essays that follow it, demanding the absolute anonymity of the publication. He successfully required that even the royal “privilege” granted in France – a kind of copyright11 – make no mention of the author’s name. The printing was finished in June 1637 and the volume began to circulate immediately, thanks above all to Descartes himself, who asked for two hundred copies to send to his correspondents: that number is not small for an author who declared himself alien to any aspiration to worldly glory (“I fear reputation more than I desire it,” he had declared a few years earlier).12 The anonymity was also more superficial than real, since Mersenne circulated the book even before it was bound, immediately revealing its authorship.13 In a short time, the learned and powerful of Europe knew the volume and its author. Descartes sent copies to the King of France Louis XIII, to Cardinal Richelieu, to Prince Frederick Henry of Orange-Nassau, Stadtholder of the United Provinces, to two important Vatican prelates, Cardinals Barberini and Guidi di Bagno, and also to one of his former teachers at La Flèche, recognizing his debt to the Jesuits and asking that the book be examined by the doctors of the Society of Jesus (not without the hope “of having them all on [his] side”).14 And, naturally, he also sent it to a great number of scientists and philosophers, among them Galileo. In 1639, finally, Descartes would willingly abandon anonymity.15
Protagonist as the object of analysis, but also and above all as subject, through its spokesman Descartes, who speaks directly in the first person: another tangible sign of Montaigne’s influence. The subjectivist point of view, however, is only apparent. Rather than describing himself, Descartes gives voice to the rational man within him, recognizing himself as not superior to the average person and even less capable than others in many things (“For my part, I have never presumed my mind to be in any way more perfect than that of the ordinary man”).18 But this very display of modesty, more than truthfully representing the author’s character – highly competitive and vain19 – is expressed in order to advance his purpose, which is to show that reason, in its potential, is equal in all men. To demonstrate this, Descartes immediately places himself under the authority of the scholastics, that is, of his own adversaries, who held that “more” and “less” apply only to the accidental characteristics of individuals of a given species, but not to their “forms or natures” – and the “rational soul” was precisely, for the scholastics, the substantial form of man. In other words, if the essence of man is to be a rational animal, reason is necessarily equal in all – and, it is implied, the guiding rules for its optimal exercise will be equally universal.
Thus, in only two paragraphs, Descartes hopes already to have won over the average reader without philosophical training – perhaps fascinated by
In this conciliatory and seemingly reassuring framework, Descartes again exploits, from the beginning, the literary device of the fable, this time in order to introduce a kind of intellectual autobiography that occupies almost the entire First Part of the Discourse and reappears in various places in the subsequent parts, providing the continuous thread of the writing. What I propose, writes Descartes, is only a “a story or, if you prefer, a fable in which, among certain examples worthy of imitation, you will perhaps also find many others that it would be right not to follow”; and he does not intend to dictate a general method for conducting reason “but only to reveal how I have tried to direct my own.”22 The rest of the text will progressively and strikingly contradict this statement – the method will even find its first warrant in God – but the boundary between individual experience and universal message is so skilfully blurred as to be often imperceptible. And this too contributes to giving the Discourse on the Method that underlying ambiguity, or that illusory clarity, which still makes it attractive and readable today beyond stale and pompous celebration.
Descartes’s autobiography begins with his time at La Flèche and his dissatisfaction with scholastic knowledge, source of doubts and errors in all those disciplines learnt with effort but uncertain and useless for life, and in particular a mathematics limited to practical applications and lacking philosophical depth. He recounts a journey in knowledge lasting almost nine years, during which he often delved into history: to read ancient books, for Descartes, is like travelling and “conversing with [men] of past centuries”. But the result is disheartening:
Until finally, tired of the world of books and of the book of the world, Descartes resolves to study himself. And it is precisely in himself that he will find the method for “distinguishing the true from the false in order to see clearly into my own actions and proceed with confidence in this life.”24
2 Four Rules and a General Principle
It may seem strange that, in a work programmatically dedicated to defining the method of human knowledge, no more than a single page is devoted to the fundamental rules of the method itself.25 Perplexity also arises from the disproportion between the broad presentation, which occupies the entire beginning of the Second Part of the Discourse, and the actual enunciation of the rules, which is quite concise. In the presentation, the aim is to show – by an elaborate argument including five examples – that reforms made by “a single individual” are much better than those elaborated by a number of different agents. In the case of science, this single reformer would naturally identify with the author of the Discourse, and the fact that one of the examples chosen by way of comparison is “God” himself – the sole author of all the precepts of true religion – shows how deeply Descartes felt himself invested with a truly important mission. As for the origin of his reflections on method, everything is once again traced back to the fateful winter of 1619–1620, when Descartes had retired to meditate in Germany – although, as we have seen, the authentic account of those memorable reflections contained nothing more, regarding method, than vague references to the unity of knowledge. Likewise, as already mentioned, in the autobiographical section of the Discourse, there is no trace of dreams or nocturnal revelations.
“The first was never to accept anything as true if I did not have self-evident knowledge of its truth: that is, to carefully avoid precipitate conclusions and preconceptions, and to include nothing more in my judgements than what presented itself to my mind so clearly and so distinctly that I had no occasion to doubt it”;
“The second, to divide each of the difficulties examined into as many parts as possible and as may be required in order to resolve them better”;
“The third, to direct my thoughts in an orderly manner, by beginning with the simplest and most easily known objects in order to ascend little by little, step by step, to knowledge of the most complex, and by supposing some order even among objects that have no natural order of precedence”;
“And the last, throughout to make enumerations so complete, and reviews so comprehensive, that I could be sure of leaving nothing out.”
Even though similar precepts can be found in the Regulae ad directionem ingenii, written only a few years earlier, it does not seem legitimate to speak of a strong continuity with that work: the horizon of Descartes’s methodological reflections has significantly changed.26 And the signs of this change are plain for all to see: simple natures have disappeared, in name and in fact (except for the mention of the “simplest and easiest objects to know” referred to in the third rule, without further specification). But not only simple natures: also absent are the other two cornerstones of the youthful work – namely, intuition and deduction – which are no longer mentioned at all. And this applies not only to the Discourse but to all of Descartes’s subsequent production. It is as if, after the Regulae, Descartes had come to distrust such concepts, no longer considering them adequate for his new speculative horizon. In some cases, there is a sort of retranslation: the intuitus of the Regulae survives, in the mature writings, in the knowledge each person has of his/her own existence as a thinking being (the cogito), and in that of the axioms attested in a non-discursive way by “natural light” – whereas, after the metaphysical turn of 1630, intuitus is excluded precisely from the domain in which its application had seemed most obvious: mathematics.27
But now Descartes is no longer willing to claim that there are notions valid in themselves, prior to any inquiry into their foundation. The question becomes, for the time being, to define what must be accepted “as true” (pour vrai), according to the subtly but decisively subjectivist nuance that characterises the first rule of the Discourse. Only afterwards will it be discovered that what we accept “as true” on the basis of its self-evidence is actually true and not an illusion: but this will require an entire metaphysics, of which the Discourse itself provides only a summary in the Fourth Part. It is, in fact, within metaphysics that it can finally be asserted that “the things we conceive very clearly and distinctly are all true”. This “general rule”, or rather principle – indeed, the Cartesian principle par excellence – is enunciated for the first time precisely in the Fourth Part of the Discourse.28 As for the foundation of such a principle, it is once again in God that it must be sought: however self-evident our ideas may be, if we did not know ourselves to be created by a perfect and infinite Being, “we would have no reason to be sure that they had the perfection of being true”.29 In short: self-evidence per se is not a guarantee of truth – a thesis simply inconceivable in the era of the Regulae.
The other three rules defined in the Discourse are closely connected, in agreement here with the Regulae, where they constituted a unified block around the notion of an “order” of knowledge. The rule of division (sometimes, but improperly, called that of “analysis”) and that of enumeration are in reality only operational precepts that allow one to apply, to its fullest extent, the third rule, that of order, which prescribes a hierarchy of cognitions from the simplest to the more complex: in short, this is the “secret” of the method, already widely disclosed in the Regulae (here too, a term sometimes used to indicate
The generic nature of the rules of the method, combined with their succinct enunciation, was not well received by all readers. Indeed, on many contemporaries, as well as on many readers in the following centuries, the four rules did not make a great impression. Even Arnauld and Nicole, authors of the Port-Royal Logic (La Logique, ou L’Art de penser, 1662), limited themselves to mentioning them briefly and without much comment: “they may be useful”.35 The ironic paraphrase of Leibniz, who compared them to the empty formulas of certain alchemists, has become famous: “Take what is needed, do what you must, and you will obtain what you desire”.36 Is that all? To be sure, the first to lend little importance to the rules of the method was Descartes himself, who never returned to them after the Discourse. In the prefatory letter to the French edition of the Principles of Philosophy (1647), in which he redesigns the whole architecture of knowledge, he devotes only a few lines to the question of method, referring to the “rules” of a logic different from common logic, to be practised before proceeding to “true philosophy”.37 By that very gesture, the whole issue of method is relegated to a mere propaedeutic.
From another point of view, however, Descartes’s method cannot be reduced to the enunciation of the four rules in the Second Part of the Discourse. The method is active throughout Descartes’s writings and is applied – without burdensome normative paraphernalia – in his philosophical practice. And this applies not so much to the texts that he himself explicitly indicates (such as
3 A Provisional Morality
Having finally – after so many hesitations – entered onto the stage of the world, Descartes experiences an impulse of prudence. To the first two parts of the Discourse, in which he boldly presents himself as the reformer of knowledge, he adds in the Third Part a digression, necessary to clarify the scope of his methodological reform founded on the rejection of all probable knowledge and on the primacy of clear and distinct ideas – a reform from which he excludes, in one stroke, morality and religion. He had already excluded politics: state reforms are always harmful, and only “folly” could lead someone not already in power to believe he could undertake one.40 However, the cases of religion and morality are quite different from one another. For religion – and in particular for revealed theology, already mentioned in the First Part – the exclusion from the procedures of the method is to be presumed definitive, but for morality it is only a temporary solution, albeit expedient while awaiting better times. This is the meaning of the “provisional” morality (par provision, in the original
Once again, he has recourse to the metaphor of houses and foundations: while constructing the new building after demolishing the old one, we need a roof above our heads, a shelter for use while the site remains unfinished. Indeed, there are actions that do not allow delay or suspension: morality is the site of our daily choices, which cannot await the completion of the entire process of reconstruction of knowledge. It is therefore necessary to clarify, from the outset, how one must act in the world while still lacking the light of science. The maxims of “provisional” morality are presented by Descartes with his usual subjectivist nuance: he claims to have conceived them for himself – like the rest of the method – during the winter of 1619–20, in his Neuburg retreat.42 It is also in the same period that he may have received as a gift (from a Jesuit!) a copy of Charron’s Sagesse – a copy still preserved in a private collection in that city, in which there is a dedication addressed to him.43 Charron’s Sagesse was a scandalous work, placed on the Index as early as 1605 and destined shortly thereafter to become the target of traditionalist authors such as Father Garasse (and even Mersenne); but it was a work that undoubtedly exerted a certain influence on the provisional morality of the Discourse.
In reality, nothing in the writings preceding the Discourse on the Method attests an engagement of Descartes in the field of morality, apart from some vague statements in the Private Thoughts concerning human free-will.44 Even admitting that he might have read Charron’s Sagesse in 1619, it is plausible to
In the third part of the Discourse, Descartes declares that “I have formed for myself a provisional moral code consisting of just three or four maxims, which I should like to tell you about.” Descartes’s first three maxims are the following:
“The first was to obey the laws and customs of my country, holding constantly to the religion in which by God’s grace I had been instructed from my childhood, and governing myself in all other matters according to the most moderate and least extreme opinions – the opinions commonly accepted in practice by the most sensible of those with whom I should have to live.” (CSM I, 122)
“My second maxim was to be as firm and decisive in my actions as I could, and to follow even the most doubtful opinions, once I had adopted them, with no less constancy than if they had been quite certain” […] “Similarly, since in everyday life we must often act without delay, it is a most certain truth that when it is not in our power to discern the truest opinions, we must follow the most probable.” (CSM I, 123)
“My third maxim was to try always to master myself rather than fortune, and change my desires rather than the order of the world.” (CSM I, 123–124)
The first maxim immediately highlights the conservative and conformist side of Descartes’s “provisional” morality, preaching acceptance of the status quo and the rejection of all extremism – a conception widely diffused at the time, with key references in Montaigne and Charron. The latter were the noble fathers, in general, of the entire tradition of libertinage érudit in the first half of the seventeenth century. The libertine sage does not present himself as a reformer of morality, much less of religion; rather, he adopts and maintains the
The rejection of all radicalism and extreme options applies not only to public decisions but also to private ones: that one ought not to restrict one’s freedom of action by contracting indissoluble bonds, is in fact a corollary of the first maxim. In the text, only commercial contracts and religious vows are mentioned: useful and praiseworthy, but not for me, affirms Descartes (and this statement would bring some reproaches down on him).48 But it is possible that he was also thinking of something else, as a brief look at his – rather bleak – emotional life confirms. In 1635, two years before the publication of the Discourse on the Method, his daughter Francine was born in Deventer, by Helena (or Eijlena) Jans van der Strom, one of his maids. Both mother and child were in fact extremely ephemeral ties, from which he would soon be freed, albeit for different reasons: Francine died in infancy in 1640; as for Helena, Descartes would secure her future by financing her marriage to the son of a Dutch innkeeper, thus freeing himself from what Baillet defines a “dangerous commitment”.49 Nor are any other romantic involvements of the philosopher known, apart from a “slightly cross-eyed” girl50 who had made an impression on him when he was a child: an episode which all biographers – even the most serious – mention for lack of better material.
What emerges from the second maxim is above all the attempt to dissociate morality from the strict canon of the Cartesian method: is it possible to behave morally well even in the absence of epistemic certainty? A probabilistic approach, however unacceptable to Descartes in physics and metaphysics, allows him to reconnect with late scholasticism, and in particular with Suárez, in the field of morals. Suárez had increasingly distanced himself from certain key theses of Aristotelianism, insisting on the intrinsic value of moral conscience: one can act with the certainty of acting virtuously even without possessing the light of truth. Probability or doubt must be distinguished from truth when science is at stake but in the practical realm it is legitimate to translate probability into certainty. Descartes follows Suárez on this point, literally reversing what had been – and would remain – his position in purely theoretical matters: whereas, in the search for truth, what is only “probable” or subject to doubt must be considered “absolutely false,” on the contrary, in moral choices, a doubtful or uncertain opinion must be considered “most true and certain,” once embraced, either because it is more probable than others or simply because a decision had to be made without further delay.53
The provisional morality concludes with a final recommendation (“Finally, to conclude this moral code”), which is in fact to be understood as an additional maxim (at the beginning of the Third Part there was indeed mention of “three or four maxims”). The register is again subjectivist: Descartes speaks of his decision to “continue my self-instruction” so as to acquire all the knowledge necessary to “to judge well”.57 But, as usual, the message is intended for everyone. Indeed, this final recommendation ultimately reveals “the sole basis of the foregoing three maxims”.58 It turns out, in fact, that the first three maxims of the provisional morality are suspended upon a condition and a condition that is anything but provisional – rather, it is foundational in all Descartes’s moral thought: that of striving to increase one’s knowledge, because practical
However, the moral analyses offered by Descartes in the Discourse have something intrinsically “provisional.” They do not include, for instance, an adequate reflection on human freedom – a topic never addressed thematically in his writings prior to the Meditations.61 The most provisional, if not precarious aspect of Descartes’s moral questioning in the Discourse lies ultimately in its moralism: the entire question of individual choices is reduced to an internal play of thoughts and opinions, conceived as mental states entirely independent from bodily conditioning. Morality seems to have nothing to do with those things that are “in man” but do not depend “on man” (that is, precisely, bodily movements).62 In the Third Part of the Discourse, the case of a possible interaction between the two components of the human being is never contemplated: the word “passion” does not appear at all.63 This is an approach that Descartes would later abandon. However, the direction in which he was heading can be inferred from a revealing phrase in the Sixth Part of the Discourse, where he states that every human good depends strictly “on the temperament and
4 The Body Machine
One of Descartes’s most revolutionary writings is the treatise on the human body which constitutes the final part of Le Monde and which would be published separately, fourteen years after his death, with a perhaps spurious title: L’Homme (generally translated as Treatise on Man).65 The Fifth Part of the Discourse contains a muted echo of this text – consistent with the cautious tone adopted throughout the work – but still enough to draw the attention of readers, particularly by the allusions it contains to one of Descartes’s most famous and infamous theses: that of animals as machines lacking any sort of thought or consciousness.
The Treatise on Man opens with a section expressly entitled “The Body Machine”. This title precisely conveys Descartes’s decisive move, the originality of which lies not so much in the use an artificial model to explain certain bodily functions (this had already been considered by the Scholastics and even by Aristotle),66 but rather in the reductionist rigour with which he proceeds in his reasoning: the human body, for Descartes, is nothing but a machine. In asserting this, he does not claim great originality from a strictly anatomical point of view. He is aware of having “nothing new” to say compared to what had already been shown by other specialists in the field, from Vesalius to Bauhin.67
In this connection, Descartes distances himself from the medical science of his time, still heavily influenced by the Galenic tradition and the theory of bodily humours; but he distances himself not so much in the single physiological explanations, as in their translation into the new language of the scientific revolution. This is the case, for example, in the analysis of digestion. Descartes follows the main lines of Galen’s explanation but eliminates all reference to supposed “faculties” and virtues of the bodily organs. His explanatory theory is entirely based on mechanical models, particularly that of the fermentation and dilation due to the overheating of particles of matter, that is, ultimately, to their vortical motion. Digestion thus consists in the breakdown of food by liquids present in the stomach, which separate its parts just as acids attack metals. The finer parts pass through small pores and flow into a large vein that carries them to the liver, where they are purified and transformed into blood, which then begins to circulate within the organism.68
Around 1630, the thesis of blood circulation was no trivial matter. William Harvey (1578–1657) had published his discovery only two years earlier, in his De motu cordis. Before that, it was believed that blood, continuously produced by the liver and heated by the heart, irrigated the body and was then extinguished in the peripheral tissues. Descartes, for his part, declared he had read Harvey only after writing his Treatise on Man.69 But we have only his word for that, and it is plausible that he came to know Harvey’s thesis even without consulting the work directly. In any case, in the Discourse on the Method and in other subsequent texts, Descartes honestly acknowledges that the discovery of circulation is the achievement of the English physician, renouncing any claim to paternity.70 In any case, Descartes’s approach is certainly different from Harvey’s. The latter regarded the heart as a muscle capable of contracting and expanding,
From a strictly medico-scientific point of view, Harvey is far more advanced than Descartes. However, Descartes is far more capable than Harvey of giving an explanation of the heart’s motion compatible with the laws of physics, reinterpreting in mechanistic terms – without any occult faculty or “pulsific virtue”72 – the classical thesis (already held by Plato and Aristotle) of the heart as the warmest place in the body. Moreover, for Descartes, the circulatory system is connected to the nervous system and the main bodily functions rely on their interaction. The nerves are small tubes equipped with an internal filament and spread throughout the organism. Inside them flow the “animal spirits,” another traditional term of Galenic origin, which Descartes borrows to indicate small particles of extremely fine matter (similar to those of the “first element”) and thus endowed with rapid motion. Descartes believes that the animal spirits are generated mechanically in the brain, which is continuously irrigated by blood: as it flows from the heart to the brain, the blood is filtered by a sort of sieve formed of cerebral tissue, which allows to pass through its pores only the smallest parts of which the blood is composed – the animal spirits – destined to pass into the nerves.73 The animal spirits have various functions, all dependent exclusively on their motion: 1) they determine and guide the contraction and relaxation of the muscles; 2) they keep the nerve filaments taut, allowing the transmission of impulses; 3) they modify the brain (in a way we will consider below) in correspondence with events in the internal and external organs of the body.
The brain is the directional centre of the entire bodily machine.74 It consists of a complex of nerve filaments capable of assuming and preserving different physical states (like the “folds” that a sheet of paper retains after being creased) depending on the stimuli received from the passage of the animal spirits. The cerebral “folds” are the seat of memory, that is, the ability to retain traces of
The analysis of the sensory apparatus constitutes perhaps the most original and fascinating section of the Treatise on Man. To explain the functioning of the five sense organs and their relationship with the brain, Descartes does not postulate the existence of any special faculty, but rigorously applies the figurative model of the Regulae, now integrating the physical aspect of the question, previously only sketched. All the messages transmitted from the nervous system to the brain consist in the agitation of the internal filaments of the nerves, which is transmitted from the sensory terminations to the brain, provoking the opening of the corresponding pores in the inner cavity of the brain. The animal spirits, coming from the pineal gland, can then flow into the nerves through these same pores, determining the motor response to the stimulus received (thus, at the first sensation of a burn, we immediately pull our foot away from the fire).79
As for sensations and emotions, they do not depend on structurally different cerebral events: only the “figures” (that is, the configurations of cerebral tissue) to which they correspond are different. Thus, the various colours, sounds, tickling, fear, good mood, and hunger differ only because they correspond to different states of cerebral matter. Sight, in particular, does not depend at all –
Just as in physics, so too in physiology, Descartes pursues a radical reductionism: in physics, he dispenses with “qualities” and “forms,” in physiology, even with the soul. For the Scholastics, the soul (which was regarded as the “substantial form” of man) was necessary for life, for locomotion, for the most basic functions of every living being, starting with sensation. The Scholastics, however, distinguished between the “vegetative soul” of plants (living but devoid of sensation), the “sensitive soul” of animals (not only living but also capable of sensation), and the “rational soul,” characteristic only of man, which contains the principle of rationality and also those of life and sensation. The first two “souls” were generally considered to be corruptible, unlike the rational soul, which, while containing the others as its inferior faculties, is nevertheless immortal.82 But Descartes intends to avoid any contamination between thought and body. For this reason, he rejects the tripartition of the soul’s faculties and reduces all lower functions to bodily matter alone, mechanically organized, the latter being sufficient to explain life, organic functions, the sensory apparatus, memory, and corporeal imagination. In the conclusion of the Treatise on Man, he argues that, “to explain these functions, then, it is not necessary to conceive of any vegetative or sensitive soul, or any other principle of movement or life, other than its blood and its spirits which are agitated by the heat of the fire that burns continuously in its heart, and which is of the same nature as those fires that occur in inanimate bodies”.83
Thus, the peculiarity of Descartes’s position does not consist merely in the claim that animals are machines, but in the subsequent assertion that they are machines without consciousness. This latter claim, moreover, is not made explicitly in the Discourse on the Method, which generates a whole series of misunderstandings. In the Fifth Part, in particular, Descartes is chiefly concerned with denying that animals have reason, thereby responding to a famous remark by Montaigne. In one of his celebrated Essays, Montaigne had sought to subvert the commonplace of man’s preeminence over animals, polemically reversing it and attributing a form of rationality to animals.87 Against Mon-taigne, Descartes reiterates that the outward acts of animals, even those that appear most human and refined, still show their lack of reason. This, for two reasons: 1) language, which is proper to man and which no animal can imitate except by producing sounds in response to certain stimuli – something a machine could also do; 2) the universality and creativity of human reason,
With this manoeuvre, Descartes perhaps hoped to ingratiate himself with the Scholastics, whom he followed by his use of the term “rational soul,” of which animals are said to be entirely deprived (on this point, indeed, the Scholastics agreed). This equivocation, perhaps intentional, generated another that was certainly unintentional. The first readers were in fact led to think that Descartes was willing to maintain that bodily organs are sufficient to produce sensations (that is: not merely responses to specific sensory stimuli, but the actual awareness of such stimuli), and thus that he was proposing a kind of materialistic theory of sensitivity – albeit limited to animals. Moreover, certain statements in the Discourse were not free of ambiguity. For instance, Descartes maintained that the machine of the body is sufficient for all those functions in which animals resemble us and which are independent of the rational soul. A Scholastic could only interpret this to mean that matter is sufficient for sensation, although not for reason. That is, indeed, how one of the first critics of the Discourse on the Method – Libert Froidmont, professor of theology in Louvain – understood it.89
At this point, Descartes was forced to clarify things. And he did so at last, but only in private. Animals, he wrote in a letter of October 1637 to Plemp, do not have a soul – but not because they are incapable of reacting to a visual or auditory stimulus with observable external behaviour. Animals are obviously capable of doing all that, as common experience shows. Moreover, they also have a form of memory, based on the persistence of traces of animal spirits in the brain, just as they have retinal images and a convergence of various nervous stimulations in the common sense. The point is that animals are not aware of possessing all these functions and capacities. A mystery? No more so, Descartes explains, than are the involuntary actions of humans, like reflex movements, which certainly do not depend on the soul, but on an internal
In reality, Descartes’s position on animal consciousness is not so rigid, and little by little he will shift from the assertive declaration of 1637 to more cautious expressions that border on agnosticism: we cannot know what animals feel – he writes to More in 1649 – because consciousness is a private fact and thus only an animal itself could testify to its possible conscious states.91 Nevertheless, the doctrine of animals-as-machines was from the beginning one of the most controversial points of Descartes’s philosophy and would lend itself to all kinds of accusations and caricatures, especially in popular publications and polemical pamphlets. What was most unacceptable was the thesis that animals are incapable of feeling pain: it seemed to open the door to every kind of sadistic cruelty towards them, including vivisection. Descartes was undoubtedly responsible for this interpretation of his thought. Although he was well-versed in animal behaviour and even owned a dog (“Monsieur Grat”), he had effectively asserted that only the “external movements that accompany pain” are to be found in beasts, and “not the pain itself”.92
Yet one last, perhaps most unsettling question remained: if the body of both man and animals is a machine, who is its designer and maker? God, replies Descartes in the first instance, both at the beginning of the Treatise on Man and in the Discourse on the Method, where he specifies, however, that only the insufficiency of available data had prevented him from treating the question “in the same style as the rest,” that is, without distinguishing the question of the origin of life from that of the origin of the universe as a whole.93 In a letter to Mersenne dating from 1639, Descartes goes so far as to postulate that the body of organized beings is formed in the same manner as the rest of matter generated from the original chaos: a machine, thus, that assembles
Finally, shortly before his death, Descartes would embark on another impossible challenge: to explain, on the basis of the laws of motion alone, the formation of the foetus in the mother’s womb. He would not succeed, for obvious reasons, but the path towards the unification of what would later be called “biology” with the other exact sciences – though still steep and long – was thus indicated.95
5 Science and Society
The Sixth Part of the Discourse on the Method – important above all in order to understand Descartes’s overall cultural programme – starts with a small exercise in rhetoric. Descartes must deny being a Copernican, while at the same time making clear – to those who are ready and able to understand – that he is a Copernican and that his decision not to disclose his physics (i.e., The World) is entirely justified. Hence we are confronted with a series of linguistic contortions, allusive descriptions, and meaningful disclaimers: “persons for whom I have particular respect” (i.e., the Roman Inquisition) disapproved of “an opinion in matters of physics” (Copernican heliocentrism) published “by someone else” (Galileo); an opinion in which I saw nothing dangerous to religion or the state but which “I do not wish to say I shared” (that is: I do not wish to say so because I am forbidden to do so, but in reality I did and still do share it); an opinion, in any case, that I could have upheld publicly “if reason had persuaded me to it” (that is: I could publicly uphold Copernicanism, of which I am rationally persuaded, but I do not do so because the Church forbids it).96
This cautious strategy is also confirmed by the three scientific essays that he offers at the end of the Discourse itself: a step back, compared to the ambitions of The World. In these, Descartes explicitly adopts a much more restricted point of view, which he considers necessary in order not to reveal too much of his physics. What is missing in these essays is precisely what was most boldly Cartesian in The World: the search for first principles, the laws of nature and their foundation, the aspiration towards a unified explanation of nature based on a few simple notions. In the Dioptrics, Descartes speaks of light, but discards from the outset the question of its “nature,”101 and starts with certain empirical data, seeking to proceed on the basis of mere “suppositions” (not in the sense that they are hypotheses, but simply because he refrains from showing how such suppositions might be deduced a priori, restricting himself to applying them to experience).102 The same precaution appears in the Meteors, which is devoted to the mechanistic explanation of meteorological phenomena such as winds, clouds, rain, hail, and snow, as well as the rainbow.103
In reality, the Sixth Part of the Discourse also makes it clear that something has changed in Descartes. The public impact of his mission is increasingly present in his mind: the time when he wrote the Regulae only for his personal use now seems the distant past. The Discourse lays out a genuine programme of scientific and cultural reform. A programme conceived for “purely human” men,106 that is, for human beings in their natural state, lacking divine grace; for men who must build their life experience in this world by themselves, using the intellect and the other cognitive faculties – but using them to the best of their ability and bringing them to their highest perfection.107 It is therefore, first of all, a matter of changing knowledge – since Descartes is unable or unwilling to change religious and political power. But the ambition to change knowledge does not aim to construct a new cathedral of thought, but to create a “practical philosophy,” by which, knowing “the power and action of fire, water, air, the stars, the heavens and all the other bodies in our environment, as distinctly as we know the various crafts of our artisans”, we may exploit them to “make ourselves, as it were, the lords and masters of nature”.108 This is the Baconian side of Descartes, generally absent (with some exceptions) from his writings prior to the Discourse on the Method.
Again like Bacon – who is the privileged reference for the entire Sixth Part – Descartes also begins to focus on the relationship between science and technology, another typical theme of the seventeenth-century scientific revolution,
Descartes personally devotes his efforts especially to the possible applications of his knowledge in optics. Hence his study of lenses and collaboration with craftsmen in the field, like Jean Ferrier, to produce instruments for manufacturing them. Specifically, Descartes evokes the fabrication of hyperbolic lenses intended for a new and more powerful telescope: an initiative that dragged on for several years without yielding the expected results. At one point, even Richelieu became involved, as Descartes’s French friends asked him to promote “the invention of telescopes”, but in the end the economic aspect of the venture also proved disappointing.110
The fact is that, in order to change knowledge and truly create a “practical philosophy,” many contributions were necessary. Not so much in the sense, as we will soon see below, of philosophical cooperation, but rather in that of a division of experimental labour. Experimentation also played a role in Descartes’s deductive physics, as the Principles of Philosophy would confirm a few years later. If the laws of physics are universal and necessary, and if the whole world is a machine, the “gears” of that machine remain unknown. And here too Bacon came to Descartes’s aid: he had to identify a crucial experiment (instantia crucis) that would determine unambiguously, by excluding all other possibilities, which particular configuration of matter underlies a given phenomenon.111 But the experiments to be carried out were many and required substantial funding. Science was expensive: the lodestone alone, Descartes would say years later, “costed Gilbert more than fifty thousand écus”. And in that context, he would explicitly mention Bacon’s Instauratio Magna and Novus Atlas, noting that in
Thus, funding was needed: public funding, essentially. Descartes had spoken of private individuals eager to invest in science back in 1632, already in connection with Bacon’s scientific program, but without much conviction.113 Years later – as Baillet reports – some noblemen would offer to support him in his investigations, but Descartes would always remain very wary regarding even this kind of patronage, partly because of his choice, attested by the “provisional morality,” not to contract ties and obligations toward anyone. In short, Descartes always believed “that it was up to the public to pay for what he did for the public”.114
However, it would be a mistake to assume that Descartes had a clear and modern vision of scientific progress as a collective endeavour, perhaps under the aegis of the state. Public funding, as Descartes presents it in the Sixth Part of the Discourse and in subsequent works, would be intended for him and for him alone: his task “could not be accomplished so well by someone other than the person who began it”.115 The call for collaboration among scientists, on which Mersenne placed all his hopes for progress, only applied to the material aspect of research, not to the great theoretical choices. In any case, Descartes’s isolation and his distance from France and the court made it highly unlikely that he would readily obtain royal stipends. And thus, public funds, moreover always requested in a rather lukewarm manner, never arrived.116
The Sixth Part of the Discourse on the Method concludes with a precise request from Descartes: that objections be addressed to him. And so they were.117 In addition to those already mentioned from Libert Froidmont, objections came from Jean-Baptiste Morin, a physician and astrologer, as well as more aggressive criticisms from Pierre Petit, the king’s engineer – himself a marginal and heterodox figure, whom Descartes treated with sovereign disdain. Petit went so far as to characterize the proof of God presented in the
However, as Descartes had feared, these objections and ensuing discussions ultimately distracted him from what he continued to regard as his primary goal: the publication of The World, a project he pursued until the summer of 1640, before it was eventually absorbed into the Principles of Philosophy.119 Instead of continuing along that path, Descartes began composing a treatise on metaphysics. This shift arose, at least initially, from his dissatisfaction with the summary of his metaphysical thought in the Fourth Part of the Discourse. There, in an effort not to antagonise “weaker minds”,120 Descartes had deliberately watered down his theses – at the risk of compromising the order of reasoning to which he was so deeply committed. Hence emerged the increasingly urgent need to intervene with a fully developed metaphysics. In April 1637, Descartes considered appending his 1629 metaphysical draft to a prospective Latin translation of the Discourse – a project that would be delayed until 1644. By July 1638, he began to think that metaphysics merited a separate and independent treatment, written in Latin. In November 1639, he confirmed to Mersenne that he was working on a discourse intended to “clarify what I have previously written on this subject”.121 Thus, while the intellectual community was expecting The World, or at the very least a treatise on physics containing the principles only partially disclosed in the Discourse and the Essays, Descartes disconcerted his readers by presenting the Meditations, completed by the spring of 1640. Upon hearing the news, Huygens was taken completely by surprise; he had anticipated a discussion on optics and lens-grinding but instead found himself confronted with “a work on the soul and divinity.”122
The decision to publish a metaphysical treatise marked indeed a complete reversal of Descartes’s private and public strategy. In 1630, when corresponding with Mersenne on the creation of eternal truths, he believed his metaphysics was too audacious to be presented before his physics had gained widespread
Descartes to Vatier, 22 February 1638 (AT I, 560; CC I, 129–30).
Descartes to Huygens, 1 November 1635 (AT I, 592; CC I, 231); Descartes to Mersenne [April 1637] (AT I, 349; CC I, 151–52).
See Descartes to Mersenne, 9 January 1639 (AT II, 481). See also Pierre Costabel’s note in Bulletin cartésien V, Archives de philosophie, 1976, pp. 445–54.
Huygens to Descartes, 24 March 1637 (AT I, 626; CC I, 149 – translation edited). Constantijn Huygens (1596–1687), State counselor of the United Provinces and father of the great scientist Christiaan Huygens, was one of Descartes’s most faithful correspondents since 1635.
For the Dioptrics (mentioned as a separate work already in Chapter 2 of The World), see Descartes to Ferrier, 8 October 1629 (AT I, 32–37; CC I, 20–27), and 13 November 1629 (AT I, 53–69; CC I, 28–37). For the Meteors, see Descartes to Mersenne, 8 October 1629 (AT I, 23; CC I, 17–18).
Descartes to Deriennes, 22 February 1638 (AT I, 458; CC I, 233).
Descartes to Huygens, 1 November 1635 (AT I, 592; CC I, 129).
Title proposed to Mersenne in March 1636 (AT I, 339; CC I, 135) and rectified almost a year later, see Descartes to Huygens, 25 February 1637 (AT I, 620–21; CC I, 146–7).
Descartes to Huygens, 25 February 1637 (AT I, 620–1; CC I, 146); Descartes to Mersenne [April 1637] (AT I, 349; CC I, 151–52).
Balzac to Descartes, 30 March 1628 (AT I, 570; CC I, 13–14 – translation edited).
Descartes to Huygens, 3 March 1637 (AT I, 622–3; CC I, 147).
Descartes to Mersenne, March 1636 and 15 April 1630 (AT I, 339, 136; CC I, 135, 60).
Descartes to Mersenne and to X***, May 1637 (AT I, 364, 369–70; CC I, 157–59).
Descartes to Wilhem, 12 June 1637 (AT I, 387; CC I 163); Descartes to Huygens, 27 June 1637 (AT I, 639–40; CC I, 167); and Descartes to Mersenne, 31 March 1638 (AT II, 85; CC I, 265 – see also Descartes to Mersenne, 19 June 1639 – AT II, 565); Descartes to [Fournet], 14 June 1637 and 3 October 1637 (AT I, 383, 455; CC I, 165, 191–92); Descartes to Huygens, 9 March 1638 (AT II, 662; CC I, 246).
Descartes to Mersenne, 19 June 1639 (AT II, 564). For the sending to Galileo, via Mersenne, see Galileo Galilei, Opere, vol. XVII, p. 226 (Marin Mersenne to Galileo Galilei, 27 November 1637).
AT VI, 1–2 (CSM I, 111).
See Gilson’s commentary on the Discourse, ed. 1987, p. 83.
AT VI, 2 (CSM I, 111–112).
Descartes’s constant fear, especially in mathematics, is that others appear to “know more than I do” (cf. Descartes to Mersenne, late December 1637 and January 1638 – AT I, 478–81, 487, 491–3; CC I, 199, 207–8). See also below, p. 222 (on the Letter-Preface to the Passions of the Soul).
On this point, see Henri Gouhier, La Pensée métaphysique de Descartes [1962], Paris, Vrin, 1999, p. 95 f. (“Une philosophie sans rhétorique”).
Descartes to Regius, end of January 1642 (AT III, 491 ff.).
AT VI, 4; CSM I, 112.
AT VI, 6; CSM I, 113–114.
AT VI, 10; CSM I, 115.
AT VI, 18–19; CSM I, 120.
A different and quite popular reading is found in Étienne Gilson’s commentary, op. cit., p. 196 ff.: “the two works, in substance, coincide”.
Intuitus will reappear only twice: see Descartes to Mersenne, 16 October 1639 (AT II, 599: “the natural light, or intuitus mentis”) and the 2nd Replies (AT VII, 140), while discussing the cogito. As for deductio, the only occurrence will be in the Entretien avec Burman (AT V, 170). The French word intuition is not attested in Descartes, while déduction occurs only once in the sense relevant here (AT IX–2, 2). Descartes speaks of a “connaissance intuitive” with Silhon [?] in 1637 (AT I, 354) and again in 1648 (AT V, 136–8, still on the cogito); an “inuitive” cognition, referred to God and the angels, is also discussed in the letter to Plemp of 3 October 1637 (AT I, 415; CC I, 177).
AT VI, 33; CSM I, 127: “I decided that I could take it as a general rule that the things we conceive very clearly and very distinctly are all true”.
AT VI, 38–39; CSM I, 130. See also ibid.: “what I took just now as a rule, namely that everything we conceive very clearly and very distinctly is true, is assured only for the reasons that God is or exists, that he is a perfect being, and that everything in us comes from him”.
See AT X, 407; CSM I, 37 (Rule XI).
See Descartes, Principles of Philosophy, 1st Part, §45–46: the perception of pain is “clear”, because it imposes itself upon the mind of the sufferer; but it is not distinct, because it is connected with and mixed with deceptive perceptions (AT VIII, 21–22; CSM II, 207–208). However, the distinction is quite unstable: in the Meditations we read that sensations are “in their own way more distinct” than intellectual ideas (AT VII, 75; CSM I, 52); see also Principles 1st Pt., §68: “pain and colour […] are clearly and distinctly perceived when they are regarded merely as sensations or thoughts” and not as “real things existing outside our mind” (AT VIII, 33; CSM II, 217).
AT VI, 33; CSM I, 127. See below, pp. 156–157, 169.
The use of the pair analysis/synthesis to indicate the second and third rules of Descartes’s method is ancient: it dates back to Nicolas-Joseph Poisson, author of the first commentary on the Discourse (1671). See G. Rodis-Lewis, L’Œuvre de Descartes, cit., I, p. 173 (and note 61). On “analysis” and “synthesis”, understood as different argumentative procedures, see below, pp. 173–177.
AT VI, 19, 21. On the propaedeutic value of mathematics, already apparent in the Regulae, see AT V, 176–77 (Conversation with Burman).
A. Arnauld, P. Nicole, La Logique, ou L’Art de penser [1662], ed. P. Clair and F. Girbal, Paris, Vrin, 1981, p. 306.
Leibniz, Die philosophischen Schriften, ed. Gerhardt, vol. IV, p. 329.
AT IX-2, 13–14.
On this point, see Descartes to Vatier, 22 February 1638 (AT I, 559; CC I, 230–231), and Jean-Robert Armogathe, “L’arc-en-ciel dans les Météores”, in Descartes, ed. Jean-Luc Marion et al., Paris, Bayard, 2007, pp. 161–176.
Descartes to X***, May 1637 (AT I, 370; CC I, 159).
AT VI, 14–15; CSM I, 118 (Discourse on the Method, Part 2).
On the sense in which the moral maxims of the Discourse are “par provision” see the remarks of Vincent Carraud and Gilles Olivo, “Une saignée pour en finir avec la morale dite ‘par provision’”, Bulletin cartésien, 48 (2017), pp. 143–147: not a temporary morality, they argue, to be surpassed by another (and better-founded), but a true morality imperfectly sketched. However, here as elsewhere, a fixist reading of Descartes’s thought clashes with his ever-evolving philosophical creativity. See infra, p. 73, on the intrinsic instability of the “morale par provision”; pp. 214–215, on Descartes’s letter to Elizabeth of 4 August 1644; and pp. 234–237, on the unheard of theory of “generosity” in the Passions of the Soul.
AT VI, 28; CSM I, 125.
See Frédéric de Buzon, “Un exemplaire de la Sagesse de Pierre Charron offert a Descartes en 1619”, Bulletin cartésien 20 (ed. 1992), pp. 1–3. However, the fact that in the dedication the Latinized name appears (“Doctissimo Amico grato et minori fratri Renato Cartesio”), which came into use only around 1640 (cf. above, p. 2, note 4), does not fail to raise some doubts about its authenticity.
See AT X, 218: “Tria mirabilia fecit Dominus: res ex nihilo, liberum arbitrium, & Hominem Deum”.
Conversation with Burman, AT V, 178. Similar expressions, more euphemistic, already occur in a letter to Pollot of 1638 (AT II, 35).
The anecdote is reported by Charles Adam in AT [1st ed.] XII, p. 345, note. For the relevant texts by Balzac, see G. Rodis-Lewis, Le Développement …, p. 442.
Descartes to Mersenne, 16 October 1639 (AT II, 593).
See AT VI, 24, and Gilson’s Commentaire [ed. 1987], p. 240, on religious vows.
Further details are provided by G. van de Ven, “Quelques données nouvelles sur Helena Jans”, in Bulletin cartésien XXXII, Archives de philosophie, 2004, pp. 10–12. On the “dangerous commitment” see Baillet, Vie, II, p. 91, who cites a testimony – who knows how reliable? – by Clerselier. Descartes speaks of Francine as “my niece” (Descartes to [Unknown]), 10 August 1637 (AT I, 393; CC I, 168).
Descartes to Chanut, 6 June 1647 (AT V, 57).
See Vincent Carraud, “Morale par provision et probabilité”, in Descartes et le Moyen-Âge, ed. J. Biard and R. Rashed, Paris, Vrin, 1997, pp. 259–279.
AT VI, 24; CSM I, 123.
AT VI, 31, 25; CSM I, 126, 123. See Vincent Carraud, “Morale par provision et probabilité”, esp. pp. 272–276.
AT VI, 25–26; CSM I, 123–124. On the sources (ancient and modern) of these positions of Descartes, see Gilson’s Commentaire, pp. 247–261.
AT VI, 8; CSM I, 114–115.
AT VI, 26; CSM I, 124.
AT VI, 27–8; CSM I, 124.
See Jean-Marie Beyssade, Descartes au fil de l’ordre, cit., pp. 237–58, who sees here the emergence of yet another Cartesian “circle”.
AT VI, 27; CSM I, 124. Cf. Descartes to Mersenne, May 1637 (AT I, 367; CC I, 158).
AT VI, 28; CSM I, 125.
The only possible exception is a passage from a fragment lgredy entitled Cartesius, of very uncertain dating (AT XI, 647–653), transcribed by Leibniz and published by Vincent Carraud in Bulletin cartésien 14, 1985 (for the year 1983), pp. 1–6.
Descartes to Reneri for Pollot, April or May 1638 (AT II, 36; CC I, 293).
In the Fifth Part of the Discourse, Descartes still mentions “hunger and thirst” as instances of “internal passions” (AT VI, 55; CSM 139), without distinguishing them from the true “passions of the soul” – on which see below, chap. 7.
AT VI, 62; CSM I, 143. On Descartes’s medicine, see below, chap. 7.
Descartes’s Treatise on Man was first published in a Latin translation (De homine) by Florentius Schuyl, in 1662. A French version appeared in Paris two years later. In August 2022, Erik-Jan Bos announced his discovery (in Leiden) of another Latin translation, see his blog “An Unknown Latin Manuscript Translation of Descartes’ L’Homme” – https://www.leidenspecialcollectionsblog.nl/articles/an-unknown-latin-manuscript-translation-of-descartes-lhomme. See also Delphine Antoine-Mahut and Stephen Gaukroger (eds.), Descartes’ Treatise on Man and its Reception, Springer, 2017.
See Dennis Des Chene, Spirits and Clocks: Machine and Organism in Descartes, Ithaca, Cornell University Press, 2001, p. 13.
Descartes to Mersenne, early June 1637 (AT I, 378; CC I, 161). On Vesalius (A. van Wesel, 1514–1564), cf. Descartes to Mersenne, 20 February1639 (AT II, 525). On Gaspard Bauhin (1560–1624), see Annie Bitbol-Hespériès, Le Principe de la vie chez Descartes, Paris, Vrin, 1990, pp. 195–209.
AT XI, 121–123. See F.A. Meschini, “La dottrina della digestione secondo Descartes. Itinerari tra testi, contesti e intertesti”, Physis, 2015/1–2, pp. 113–164; Carmen Schmechel, “Descartes on fermentation in digestion: iatromechanism, analogy and teleology”. The British Journal for the History of Science, 55, 2022; pp. 101–116.
Descartes to Mersenne, November or December 1632 (AT I, 263; CC I, 101).
See AT VI, 50; CSM I, 136. On Descartes and Harvey, see E. Gilson, Études sur le rôle de la pensée médiévale dans la formation du système cartésien [1930], Paris, Vrin, 1987, pp. 51–100.
See AT VI, 51–53; CSM I, 136–138.
The thesis of the vis pulsifica of the heart was already present in Galen; see W. Pagel, New Light on William Harvey, 1976, p. 72.
AT XI, 130–131. Cf. Descartes to Vorstius, 19 June 1643 (AT III, 688).
For a recent reappraisal of Descartes’s neurophysiology, see the papers collected in Denis Kambouchner, Damien Lacroux, Tad M. Schmaltz, & Ruidan She (eds.), The Cartesian Brain: Philosophical and Scientific Perspectives, New York, Routledge, 2025.
See A. Bitbol-Hespériés, Le Principe de la vie, p. 195 ff.
Descartes to Meyssonnier, 29 January 1640 (AT III, 19). Cf. Franco A. Meschini, “The Doctrine of the Pineal Gland: A Cryptic Doctrine”, in The Cartesian Brain, 2025, pp. 19–41.
AT XI, 174–178.
AT XI, 131.
AT XI, 142 ff.
AT VI, 85 (Dioptrics). Descartes offers a caricatural description of the scholastic thesis: see D. Perler, “Descartes, critique de la théorie médiévale des species”, in Descartes et le Moyen-Age …, pp. 141–53.
AT XI, 174 ff., 185–187.
Hence Descartes’s objection: how is it possible that “the sensitive soul, when it is alone, is of a corporeal and mortal nature, while, when it is united with the rational soul, it is spiritual and immortal”? (Descartes to Plemp, 3 October 1637 – AT 415; CC I, 177).
AT XI, 201–202 (Gaukroger, p. 169).
AT XI, 119 (Gaukroger. p. 99).
AT X, 415; CSM I, 42: “We refuse to allow that [animals] have any awareness of things but merely grant them a purely corporeal imagination.” Another early, but cryptic, reference to the soul of animals can be found Descartes’s letter to Mersenne of 27 May 1630 (AT I, 154; CC I, 63).
In the 2nd Replies (AT VII, 160) and then in the Principles of Philosophy, Pt. I, §9.
See Montaigne, Essays, II, 12, and the passages cited in Gilson’s commentary, p. 426 (1987 ed.).
AT VI, 57–59; CSM I, 140–141.
See Froidmont’s letter to Plemp, 13 September 1637 (AT I, 403), in reference to AT VI, 46; CSM I, 134: “when I looked to see what functions would occur in such a body, I found precisely those which may occur in us without our thinking of them, and hence without any contribution from our soul (that is, from that part of us, distinct from the body, whose nature, as I have said previously, is simply to think). These functions are just the ones in which animals without reason may be said to resemble us. But I could find none of the functions which, depending on thought, are the only ones that belong to us as men; though I found all these later on, once I had supposed that God created a rational soul and joined it to this body in a particular way which I described.” On this point, see especially Sergio Landucci, La mente in Cartesio, Milan, F. Angeli, 2002, pp. 39–54.
Descartes to Plemp, 3 October 1637 (AT I, 413; CC I, 176). For the (Pavlovian ante litteram) example of the dog, see Descartes to Mersenne, 18 March 1630 (AT I, 134; CC I, 56). For the example of the fall: AT VII, 229–230. On the topic: Georges Canguilhem, La Formation du concept de réflexe aux XVIIe et XVIIIe siècles, Paris, PUF, 1955, pp. 27–57.
See especially Descartes to More, 5 February 1649 (AT V, 276–277 – my italics): “Although I hold it as demonstrated that thought cannot be proven to exist in brute animals, I do not therefore think it can be demonstrated that none exists, because the human mind does not penetrate their hearts”.
Descartes to Mersenne, 11 June 1640 (AT III, 85). On Descartes’s dog, see Baillet, Vie, II, p. 456.
AT VI, 45.
Descartes to Mersenne, 20.2.1639 (AT II, 525).
On De la formation du fœtus, an unfinished work dating back to around 1648, cf. D. Des Chene, Spirits and Clocks, cit., pp. 32–52, and V. Aucante, La Philosophie médicale de Descartes, Paris, PUF, 2006, pp. 297–329.
AT VI, 60.
Huygens to Descartes, 24 March 1637 (AT I, 626; CC I, 149); see however Jacobus Revius, Statera philosophiae cartesianae, Lugduni Batavorum, P. Leffen, 1650, pp. 54–58.
Huygens to Descartes, 28 May 1639 (AT II, 680).
Descartes to Mersenne, [April] 1637 (AT I, 348–9; CC I, 151).
Descartes to [Unknown], May 1637 (AT I, 370; CC I, 158–159).
AT VI, 83; CSM I, 152: “I need not attempt to say what is its true nature”.
Cfr. AT VI, 76; CSM I, 150. As to Descartes’s reticence in the essays published with the Discourse in 1637, see Descartes to Morin, 13 July 1638 (AT II, 201; CC I, 322); Descartes to Mersenne, 9 January 1639 (AT II, 483); Descartes to Debeaune, 30 April 1639 (AT II, 544).
AT VI, 233.
AT VI, 392–393. See Michel Serfati, “Constructivisme et obscurités dans la Géométrie de Descartes”, in Mathématiciens français du XVIIe siècle: Descartes, Fermat, Pascal, ed. M. Serfati and D. Descotes, Clermont-Ferrand, Univ. Blaise Pascal, 2008, pp. 11–44.
Descartes to Mersenne, 4 April 1648 (AT V, 142).
AT VI, 3: “hommes purement hommes” (expression omitted in the English translation). “More than a mere man” is instead he who, aided by the grace of God, becomes capable of examining revealed truths (AT VI, 8; CSM I, 114).
On this humanistic theme in Descartes, see Emmanuel Faye, Philosophie et perfection de l’homme. De la Renaissance à Descartes, Paris, Vrin, 1998.
AT VI, 62; CSM I, 142–143.
AT VI, 62; CSM I, 143.
Descartes to Mersenne, 25 January 1638 (AT I, 501; CC I, 212).
Bacon, Novum organon, II, 36. However, while for Bacon the instantia crucis reveals, a posteriori, the cause of a phenomenon, for Descartes it only allows one to choose between various explanations compatible with the first principles, the latter being valid a priori.
Cf. AT VI, 72; CSM I, 148, and AT XI, 320 f.
Descartes to Mersenne, 10 May 1632 (AT I, 251–2; CC I, 97–98).
Baillet, Vie, II, p. 462, based on testimony by Clerselier.
AT VI, 72; CSM I, 148 (Discourse on the Method, 6th Part).
On the pension Descartes was promised in 1648, see below, p. 219.
Descartes lists the various objections received in the letter to Mersenne of 29 June 1638, giving different judgments on them (AT II, 191–192).
See C. de Waard, “Les objections de Pierre Petit contre le Discours et les Essais de Descartes”, Revue de métaphysique et de morale, 1927, pp. 53–89 (pp. 80–81); Claudio Buccolini, “Dalle Objections di Pierre Petit contro il Discours de la méthode alle Secundae objectiones di Marin Mersenne, in Nouvelles de la République des lettres, 1998, I, pp. 7–28 (but cf. Emanuela Scribano, “Traces of the Atheist. From Lessius to Descartes via Vanini, Mersenne, and Petit”, in Id., Descartes in Context. Essays, Oxford, OUP 2022, pp. 146–167).
See Descartes to Mersenne, 6 August 1640 (AT III, 146).
Descartes to Mersenne, April 1637 (AT I, 350; CC I, 152).
See respectively: Descartes to Mersenne, April 1637 (AT I, 350; CC I, 152), 27 July 1638 (AT II, 267; CC I, 348) and 13 November 1639 (AT II, 622).
Huygens to Descartes, 24 July 1640 (AT III, 749–50).
Descartes to Mersenne, 15 April 1630 (AT I, 144; CC I, 60): “I believe you already heard me say I had planned to put something of this [that is, of his early metaphysical reflections] in writing. But I do not consider it appropriate to do so until I first see how my physics will be received”.