DANIEL, GABRIEL (1649–1728). A French Jesuit who taught rhetoric, philosophy, and theology at Rennes, and eventually became librarian of the Jesuits in Paris. Daniel was a critic of Cartesianism who attacked Descartes’s philosophy in Voiage du Monde de Descartes (1690), and also in a sequel to this work, Nouvelles difficultés proposées par un péripaticien (1693). In both works, Daniel imagines travelling as a disembodied Cartesian soul through the Cartesian heavens, discussing issues in Cartesian natural philosophy with various of its proponents, including Descartes himself. The texts were an enormous success, appearing in several editions and translations. Pierre-Daniel Huet reported that his reading of the Voiage prompted him to write his own satirical account of Descartes’s life in Nouveaux mémoires (1692).
DEATH. According to Descartes, death never occurs through the fault of the soul but because one of the main parts of the body (the brain, the heart) is no longer working, or more precisely because the “fire without light” which is in the heart ceases to “burn” (Passions II, art. 122, AT, vol. XI, p. 418). At that point there is no longer any means of reviving it. Still, the only difference between a dead body and a living body is the one that holds between a clock that works and a broken clock—both are part of nature and subject to the laws of nature. Undoubtedly the fact that the animal machine is self-regulating (see automata) and adapts itself to a changing environment led Descartes to believe that life can be prolonged almost indefinitely, provided nothing interferes with it. Thus he writes to Constantijn Huygens in 1637 that he is quite confident that one day he will be a hundred years old: “For it seems evident to me that if only we abstain from certain mistakes we make in our way of life, we could live longer and happier” (December 4, 1637, AT, vol. I, p. 649; cf. June 6, 1639, AT, vol. II, p. 682).
The complexity of vital phenomena and the impossibility to control disease, however, were the reasons why eventually Descartes found more satisfaction in moral philosophy, which teaches us not to be afraid of death, than in medicine. Fear of death can be eliminated by knowing the nature of the soul as it can subsist without the body, but also by understanding that the soul is capable of many joys not found in this life and that we are part of a greater whole (family, society, state) for which we must be prepared to die. This does not mean that we should seek death; on the contrary, “one of the points of my moral philosophy is to love life without being afraid of death” (to Mersenne, January 1639, AT, vol. II, p. 480). Therefore, although we must be prepared to die, we must act as if we could reach an extremely old age. See also IMMORTALITY.
DEBEAUNE, FLORIMOND (1601–52). Florimond Debeaune (or, less correctly, de Beaune) was born on 7 October 1601 in Blois and was educated in Paris, where he also studied law. Like other mathematicians of his day he was not a professional, and became a councilor to the court in Blois. He proved that (xy + bx), (–dy + bx), and (bx – x) can be represented by hyperbolas, parabolas, and ellipses respectively.
It is not known how and when Descartes knew Debeaune, but from 1638 on he figures more or less frequently in the correspondence as someone interested in optics who shares Descartes’s interest in hyperbolic lenses. Indeed, Descartes hoped that Debeaune would succeed where he had failed, namely, in constructing a machine for grinding them. Descartes also thought highly of his mathematical expertise and his work in music theory and took the trouble of answering many of Debeaune’s questions; but he was less satisfied with his achievements in mechanics and natural philosophy, which in his view were vitiated by the fact that Debeaune followed Galileo Galilei. In a general way Descartes was glad for Debeaune’s support, if only because it contrasted favorably with the hostile reactions of “greater geometers,” such as Pierre de Fermat, Jean de Beaugrand, and Gilles Personne de Roberval. Inversely, he was disappointed when Debeaune proved to think as highly of Thomas Hobbes as did Marin Mersenne and was unable to understand his Meditations. Although Descartes did not meet Debeaune before 1644, he developed warm feelings for him and was very disturbed when Mersenne told him that Debeaune was seriously ill and possibly dead. Apart from the “Notes brièves” which Debeaune contributed to the Latin translation of Descartes’s Geometry, he did not publish anything else.
DEDUCTION. According to Descartes, deduction is one of the two fundamental ways of knowing things, the other one being intuition or also experience. The general theory of deduction has been the object of philosophical investigation since classical times. Aristotle’s theory of the syllogism codified an important class of deductive forms, and the study of logic in Descartes’s day was strongly influenced by Aristotle’s writings. Descartes’s general epistemology founds all knowledge on direct and immediate intuition of primary truths such as “nothing comes from nothing.” In addition to these primary truths, Descartes recognized that deductively valid inferences from such truths would also provide secure knowledge. In Descartes’s favored metaphor, a deductive inference is like a chain, and he speaks in the second part of the Discourse on Method of “those long chains of completely simple and easy reasoning that geometers commonly use to arrive at their most difficult demonstrations” (AT, vol. VI, p. 19).
For Descartes, the aim of the method is to teach how to use intuition and how to find deductions. Descartes defines deduction as “an inference of something following necessarily from some other things known with certainty” (Rules III, AT, vol. X, p. 369). In opposition to experience, which can be deceptive, “the deduction or pure inference of one thing from another can never be performed wrongly by an intellect which is in the least degree rational, though we may fail to make the inference if we do not see it” (Rules II, AT, vol. X, p. 365). So either a deduction is made, and then it is right, or it is not made at all. This shows that Descartes is not thinking of deduction as the application of the laws of logic; on the contrary, “those chains with which dialecticians suppose they regulate human reason seem to me to be of little use here, though I do not deny that they are very useful for other purposes” (Rules II, AT, vol. X, p. 365). In fact, what he has in mind is the type of deduction used in mathematics, when we “see” how different propositions relate to each other and how an unknown truth follows from one or two truths already known, or in music, where we can “deduce” a table of consonants once we know the principle. Thus, deduction is nothing but an attentive comparison of two or more things and seeing the relations between them. All we need therefore to deduce things in the right way is “sagacity.”
Although intuition and deduction are different in the sense that deduction involves more than one element, they both rely on a form of seeing the truth: “very many facts which are not self-evident are known with certainty, provided they are inferred from true and known principles through a continuous and uninterrupted movement of thought in which each individual thing is clearly intuited” (Rules III, AT, vol. X, p. 369). While deduction is reliable, Descartes consistently ranks it as less worthy than immediate intuition. The reason for this relative priority of intuition over deduction lies in the fact that intuition is instantaneous and requires no recourse to memory or other potentially faulty cognitive processes—to intuit the truth of a first principle is to see its truth in a way that rules out any possibility of error. Deduction, on the other hand, requires a kind of “movement” from accepted premises to inferred conclusion, and this means it must have at least some recourse to memory, especially in the case where a very long demonstration depends on establishing intermediate results. As Descartes put the matter in the Rules, “we distinguish the intuition of the mind from certain deduction by the fact that we are aware of a movement or some sort of succession in the latter, but not in the former, and furthermore because immediate self-evidence is not necessary for deduction, as it is for intuition; rather, deduction in some sense gets its certainty from memory” (Rule 3; AT, vol. X, p. 370). Given the fact therefore that memory may be uncertain, deduction should be frequently confirmed by an enumeration. In later works the term seems to lose its specific meaning and is applied even to the type of deduction Descartes usually rejects, namely, syllogistic inference.
DEMON, EVIL. See DOUBT.
DEMONSTRATION. In the tradition of logic following Aristotle’s Posterior Analytics, a demonstration is a special kind of syllogism, namely one whose premises are true, better known than the conclusion, and related to the conclusion as cause to effect. In the “Geometrical Appendix” to his reply to the second set of Objections Descartes distinguished between two modes of demonstration—analysis and synthesis (AT, vol. VII, pp. 156–57). A synthetic demonstration satisfies the traditional definition, while an analytic demonstration begins with what is known or sought and works “backward” to uncover the clear and distinct ideas that form the basis of all real knowledge. It is the intuition of such ideas that must form the basis for any demonstration, and these are obtained by focusing the mind on the clear ideas of the intellect rather than those provided by the sensation. As Descartes explained to Marin Mersenne, his proofs for the existence of God are “more clear in themselves than any demonstrations of the geometers; in my view they only seem obscure to those who don’t know how to withdraw the mind from the senses” (AT, vol. I, pp. 350–51).
DESARGUES, GIRARD (1591–1661). French mathematician, credited with founding projective geometry, although his contributions were largely ignored until the 19th century. Born to a wealthy and influential aristocratic family in Lyon, Desargues came to Paris in 1626 and became active in the circle of mathematicians around Marin Mersenne, which included Descartes, Gilles Personne de Roberval, Claude My-dorge, Jean de Beaugrand, and Blaise Pascal. Desargues had a lifelong interest in applied mathematics, especially in the use of perspective by architects and stonemasons, and in 1636 he published a treatise on perspective, Exemple de l’une des manières universelles . . . touchant la practique de la perspective. He developed ideas taken from the theory of perspective into a geometric theory he applied to conic sections in his Brouillon projet d’une attainte aux événemens des rencontres d’un cone avec un plan (1639). Desargues’s treatise took as its point of departure Johannes Kepler’s principle of continuity, according to which the conic sections are members of the same closely related family of curves; a circle, for instance, can be transformed into an ellipse by continuous motion, and the ellipse into a parabola by removing one focus to infinity. Using techniques from the theory of perspective, Desargues considered geometric figures as “projected” into a plane in the same way that painters represent three-dimensional objects as two-dimensional projections on a canvas. He then showed that although shapes and sizes of geometric figures changed according to the plane of incidence in which they are projected, certain essential properties remain invariant under projection, and these became the object of his study.
Desargues maintained a cordial relationship with Descartes, supporting him in his disputes with Pierre de Fermat and Beaugrand (with whom he quarreled independently). He offered to enlist the aid of Cardinal Richelieu in having lenses ground in accord with Descartes’s optical theories, but the project came to nothing after Descartes expressed reservations, complaining that “if someone should work on this without my direction, I suspect that he would not succeed on the first try, and would perhaps attribute the mistake to me in order to excuse himself” (AT, vol. I, p. 501). The significance of his own geometric work was shrouded both by his penchant for a convoluted and eccentric language that made the full generality of his results difficult to appreciate, as well as his failure to exploit the algebraic methods which had made Descartes’s analytic techniques so powerful. Desargues did not publish his works for a wide readership; he was content to print a small number of copies to be distributed to other mathematicians. As a result, his work in projective geometry fell into obscurity. Only with the reinvention of the subject by Gaspard Monge and his pupils in the 19th century did Desargues’s contributions become widely known.
DESCRIPTION OF THE HUMAN BODY (DESCRIPTION DU CORPS HUMAIN). After Descartes put into order a neat copy of what was later known as the Treatise on Man (“Traité de l’homme”) in 1640–41, he seems to have neglected human biology. The reason was that he needed more experiments than he could do, which was also the reason why neither animal nor human biology was treated in the Principles. In the winter of 1647–48, however, Descartes started writing a new work containing “a description of the functions of animal and man” which would also contain an explanation of “the way an animal is formed from the beginning” (to Elisabeth, 25 January 1648, AT, vol. V, p. 112). This is confirmed by a remark in the so-called “Conversation with Burman” of 1648, where a “Treatise on Animals” is mentioned, on which Descartes had still worked “last winter” (AT, vol. V, p. 170). The occasion of rethinking animal biology may be provided by the work on the Passions of the Soul, by which however the Description was presumably also superceded—indeed, the physiological part of the Passions is by far the most complete that was published during Descartes’s lifetime. In any case Descartes never finished the work. The program spelled out at the beginning of the text announces not only discussions on the movement of the heart and on nutrition, but also on animal spirits, perception, imagination, and memory, but it is not carried out beyond nutrition. After a long “digression” (consisting of two chapters) on embryology the text abruptly ends. The part on embryology is also its main interest, given the fact that that subject is not treated in any other work, although Descartes was already interested in it in 1632 (to Mersenne, June 1632, AT, vol. I, p. 254).
The Description was among the papers left by Descartes when he died in Stockholm. Claude Clerselier posthumously published it in 1664 as a sequel to the Treatise on Man. Although it was given the title “Description du corps humain” (which may or may not be Descartes’s but vaguely corresponds to the formula used in the letter to Elisabeth), the title page announces it as Treatise on the Formation of the Fetus (“Traitté de la formation du foetus”), which is also the running title at the head of the pages. In it Descartes defends an epigenetic view of the formation of the embryo, claiming that it is initially produced by the coming together of male and female seed, which being heterogeneous, cause some sort of fermentation out of which grows the heart. In that view Descartes was practically alone, not only in the 17th century, but also in the Cartesian school, who adopted a preformationist view (the idea that the embryo is preformed in the male or the female “seed”).
DESGABETS, ROBERT (1610–78). A Lorraine Benedictine who was a partisan both of the new Cartesian philosophy and of Jansenist theology. Desgabets held various academic and administrative posts in his order. During a brief stay in Paris toward the end of the 1650s, Desgabets joined in the discussions of Cartesian physics in the private academies there, and even composed his own treatise on a technique for blood transfusion. Earlier in this decade, Descartes’s literary editor Claude Clerselier had drawn him into disputes concerning Descartes’s claim in correspondence with Denis Mesland concerning transubstandation. Desgabets defended this account in an anonymous pamphlet, Considérations sur l’état présent, that was published in 1671 and was promptly condemned by the French royal confessor Jean Ferrier as “heretical and very pernicious.” Even the fellow Jansenist and Cartesian Antoine Arnauld criticized this pamphlet, and Desgabets’s order was prompted by the controversy to prohibit him from speaking out publicly on theological matters. Ferrier’s condemnation of the pamphlet also coincided with a decree from Louis XIV that requested the suppression of anti-Aristotelianism at the University of Paris. This decree marks the start of an official campaign against the teaching of Descartes in the French schools and religious orders that continued until the end of Louis’s reign.
In his pamphlet, Desgabets defended Descartes’s account of transubstantiation by appealing to his own doctrine of the “indefectibility” or indestructibility of matter. In an early, unpublished work on this doctrine, the “Traité de l’indéfectibilité des créatures” (ca. 1654), Desgabets defended it by appealing to Descartes’s claim that God is the free cause of eternal truths. Desgabets argued that such truths are grounded in created substances that have an atemporal and therefore immutable existence.
Desgabets only published philosophical text was his Critique de la critique de la recherche de la vérité (1675), a response to the critique of Nicolas Malebranche’s Recherche by the French skeptic Simon Foucher. Malebranche professed himself to be displeased by this response, which offered an argument for the existence of the external world that conflicts with his own claim that we see bodies through ideas in God. Desgabets’s most systematic exposition of his philosophical views occurs not in his Critique, however, but in the “Supplément de la philosophie de M. Descartes” (1675), his unpublished commentary on the Meditations. In addition to further developing his version of Descartes’s account of the eternal truths there, he further defended two controversial claims that he took to undermine the Cartesian method of beginning philosophical investigation with hyperbolic doubt of the existence of the external world. The first claim is that all of our ideas of substances correspond to objects that exist external to those ideas. Here Desgabets took himself to be developing Descartes’s “truth rule,” according to which all of our clear and distinct perceptions are true. The second claim is that the nature of time reveals that our temporal thoughts depend essentially on the mind-body union, and in particular with the union of our thought with bodily motion. Desgabets appealed to this claim in rejecting the implication of Descartes’s discussion of the cogito that we have knowledge of our existence as thinking things that does not presuppose any knowledge of body.
These controversial features of Desgabets’s version of Cartesianism were the primary topic of discussion at a series of conferences held at the Commercy chateau of Cardinal de Retz, a former leader of a rebellion against the monarchy in the late 1640s (the Fronde). This version of Cartesianism also gained a following in the Lorraine Benedictine monasteries, though the publication of an official edition of Desgabets’s works was thwarted by officials due to concerns over the suspect nature of his theological views. Outside of the Benedictine order, Desgabets’s most prominent admirer was the French Cartesian Pierre-Sylvain Régis, who called him “one of the greatest metaphysicians of our century.” This compliment is reflected in the fact that Régis took over Desgabets’s views on the eternal truths, the correspondence of ideas to external objects, and the essential nature of the union of temporal thought with motion.
DESIRE. Together with admiration, love and hatred, joy and sadness, desire is one of the six primitive passions for Descartes. It is distinguished from those other passions by the fact that its object is in the future and that it has no opposite. Descartes defines it as “an agitation of the soul, caused by the spirits, which causes the soul to will the things it represents to itself as suitable” (Passions II, art. 86, AT, vol. XI, p. 392). There is no contrary passion because aversion also springs from desire. There are as many forms of desire as it can have different objects. It is also an ingredient in other passions, like hope, despair, jealousy, etc. It is based on a violent motion of the heart, causing an abundant flow of animal spirits to the brain, which in turn sharpens the senses and makes all parts of the body more mobile. However, this happens only if the desired object is imagined as being obtainable. Otherwise the agitation remains limited to the brain, where it engenders a kind of indolence or languor. As long as desire is based on true knowledge and is not excessive, it is always good. If it is based on a passion it can also be bad. It is indispensable in the economy of the passions because without it no passion could ever lead to an action.
DIGBY, SIR KENELM (1603–65). English natural philosopher, naval commander, and diplomat. Born to a wealthy aristocratic family, Digby attended Gloucester Hall, Oxford from 1618–20, but left without taking a degree. He toured throughout continental Europe in 1620–23, ending in Madrid where his uncle was the English ambassador. The Prince of Wales (later Charles I) came to Madrid in 1623 on a matrimonial mission and Digby became a member of his household. He accompanied the prince on his return to England after the failure of that mission, was knighted later in the year and became a member of the prince’s privy council. In 1627–28 Digby led a successful privateering expedition against French ships in the Mediterranean, an exploit that earned him an appointment as naval commissioner from 1629 to 1635. The death of his wife Venitia in 1633 affected Digby greatly; he withdrew from public life and spent two years at Gresham College in London studying various topics in natural philosophy, including magnetism, optics, and physiology. In 1636–37 Digby was in France, where he met Thomas Hobbes and Marin Mersenne and became an active participant in the “Mersenne circle.” By 1639 Digby had returned to England, but in the political climate of the time his Catholicism (which had not previously hindered his career) made him a target of Protestant radicals, who were concerned that his close relationship with Charles I might assist a reconciliation between the Church of England and the Roman Church. In 1641 he was summoned to face charges in Parliament and was imprisoned in 1642. He was discharged after a few months, on the condition that he accept exile in France.
Digby left England for Paris, where in 1644 he brought out his most important work, the Two Treatises, one of which dealt with the nature of body and the other with the nature of the human soul. Paris remained Digby’s principal residence for a decade, but between 1645 and 1648 he undertook two diplomatic missions to Rome in the company of Thomas White to negotiate on behalf of the exiled queen, but these missions delivered no concrete results. After his return to England in 1654 he was a confidant of Cromwell, who employed his diplomatic skills in several foreign diplomatic affairs. Notwithstanding his service to Cromwell, Digby was well received by Charles II at the Restoration in 1660. Digby’s remaining years were devoted primarily to the study of natural philosophy. He joined the Royal Society in 1660 as one of its earliest members and served on its council in 1662–63.
Digby’s natural philosophy combines Aristotelian, atomist, and Cartesian themes. It is best characterized as an attempt to retain certain Aristotelian categories (such as the theory of four elements) while embracing a broadly mechanistic account of the world in which local motion and impact are fundamental explanatory principles. Digby’s insistence in the Two Treatises on an essential distinction between soul and body, in which the soul’s “operations are such, as cannot proceed from those principles [of body],” met with Descartes’s approval, although he had no great enthusiasm for Digby’s Aristotelian leanings.
Descartes first mentions Digby in a letter to Mersenne in June of 1638, remarking that he “is much obliged to M. Digby for what he says so favorably of me,” and in another letter from August of the same year he tells Mersenne that he has “received the writing against me that M. Digby addressed” (AT, vol. II, p. 192, p. 336). Just what hostile work Descartes is referring to here remains obscure, as does the nature of Digby’s response, but the two men were clearly on good terms. This is made more evident in Descartes’s description of himself as “extremely concerned” at the news of Digby’s imprisonment in 1642 and “relieved” to hear that he had been released (AT, vol. III, p. 582, p. 590). According to Adrien Baillet, Digby “had long and frequent talks [conférences] with Descartes at the College of Boncourt,” during Descartes’s 1644 stay in Paris, which apparently dealt with Digby’s account of mind and body as it was worked out in his Two Treatises (Baillet, Vie de M. Descartes, vol. II, p. 244).
DIOPTRICS (DIOPTRIQUE). Although the Dioptrics (a treatise on refraction) was published in 1637 as one of the “essais” belonging to the Discourse, it is one of Descartes’s earliest works, presumably started in his Parisian period (1625–28), when he worked with Claude Mydorge. The work is first mentioned by name in a letter to Marin Mersenne of November 25, 1630. Toward the end of the letter it becomes clear that it is the first work Descartes intended to publish: “My Dioptrics will teach me whether I am capable of explaining my ideas and convincing others of a truth of which I have convinced myself—that which I do not believe” (AT, vol. I, p. 182). The indications are that most of it was ready when Descartes came to the Low Countries. What Descartes lacked as yet was a machine for grinding hyperbolic lenses in a controlled way, which he hoped to realize there. Descartes did not work on Dioptrics as he had planned in Franeker, not only because Jean Ferrier, a Parisian artisan he invited to work with him, but possibly also because Adriaan Metius (1571–1635), Franeker professor of astronomy (to whose brother Jacobus Descartes attributed the invention of the telescope) did not meet his expectations. Back in Amsterdam, Descartes’s thoughts were soon occupied by his plan to write a general physics (see The World). Still, a treatise on refraction is sometimes mentioned in his correspondence.
In 1632 Descartes sent Jacob Golius, professor of oriental languages and mathematics in Leiden, a copy of his “Analyse” (presumably an early version of the Geometry) and Dioptrics, apparently because Golius wanted to do some experiments. In April 1632, Golius told Constantijn Huygens that the Dioptrics was almost ready and, in a letter of June 1632, Descartes told Mersenne that he would not leave Deventer (where he had settled the previous May) before he had finished the Dioptrics. In the first week of April 1635, Descartes finally read parts of his work in Amsterdam to a party that included Huygens, who received the text from him two weeks later. In fact, Descartes’s problem was the same as when he came to the Low Countries: although he had the design of a machine for grinding hyperbolic lenses (the same presumably he submitted to Ferrier) it proved unpractical. In any case, no lens cutter seemed ready to try it out, since they were used to the traditional “tour,” or spinning top, the use of which Descartes forbid because it caused an irregular surface. Even so, Huygens urged Descartes to publish his work—to which Descartes finally consented. This is the start of the project of the Discourse, ultimately published almost two years later, in the summer of 1637. In March 1636 Descartes had already decided that the work would consist of four treatises in French: Dioptrics, Meteors, and Geometry, preceded by “the plan of a universal science by which our nature can be elevated to the highest level of perfection” (AT, vol. I, p. 339).
Of the works composing the Discourse, the Dioptrics was printed first, starting presumably in May 1636. The engraver worked on it in June, at any rate, and it was finished at the end of October. On January 1, 1637, Descartes had the printed text sent to Huygens to forward it by diplomatic mail to Paris, where it was needed in connection with the French printing license. As the result of an indiscretion of the censor, Jean de Beaugrand, the work was shown to others, particularly Pierre Fermat and Gilles Personne de Roberval. The news that Descartes was publishing a book began to spread in Paris. See also OPTICS.
DISCOURSE ON METHOD (DISCOURS DE LA MÉTHODE, DISSERTATIO DE METHODO). The Discourse on the Method of Rightly Conducting one’s Reason and Seeking the Truth in the Sciences was Descartes’s first publication (1637), which in its original form also comprised “dioptrics, meteorology, and geometry which are applications of that method.” The whole was meant as a kind of prospectus of the new philosophy, a presentation of its main achievements so far, preceded by an introduction on the method used, which in turn would be not only the reason for its success, but also its main distinction. When, at the end of 1633, the condemnation of Galileo Galilei caused Descartes to decide that he would never publish anything, he did not stop working. For one thing he carried on with the second part of the original Treatise on Light, on human biology, and he also continued to work on the Dioptrics and the Meteors. From 1635 on Descartes was much encouraged in these efforts by Constantijn Huygens and Jacob Golius (1596–1667, a Leiden professor of oriental languages and mathematics), both of whom had a keen interest in optics. It is they, together presumably with Henricus Reneri, who pressed Descartes to revisit his decision and to publish, if not a work on the whole of physics, some samples of “subjects which, without being highly controversial and without obliging me to reveal more of my principles than I wished, would nonetheless show quite clearly what I can, and what I cannot, achieve in the sciences” (Discourse VI, AT, vol. VI, p. 75).
The evolution of this project can be followed closely in the correspondence with Huygens and Marin Mersenne. In September or October 1635 Descartes decided to publish his Dioptrics with the Leiden Elzeviers, but the plague prevented him from going to Leiden and to supervise the printing. In November he added the Meteors and decided that the whole would be preceded by a short introduction, which corresponds presumably to the actual Sixth Part of the Discourse. When in January 1636 Descartes finally did move to Leiden, Elzeviers no longer showed any interest and Descartes sought another publisher and even considered the possibility of having his book printed in France. But the delay also allowed him to revise his plans and include some other work as well. At that point Descartes thought of a book of 50 to 60 leaves (that is, 200 to 280 pages), which would consist of four parts: a first part in which he presents his method and proves the existence of God and the incorporeality of the soul; a second containing his thoughts on light and vision; a third on meteorology; and a fourth on geometry. A few months later he decided to publish his book with the Leiden publisher Jean Maire (or Le Maire), with whom Descartes signed a contract on December 2, 1636. The drawings for the engravings were made by Frans van Schooten.
Since it was Descartes’s intention to obtain not only a Dutch privilege (which was granted on December 20, 1636), but also a French privilège (to protect the publisher’s interests in France and to be safe in case of future publications in France), Descartes had to submit to the censor either the entire manuscript or an important part of it. This was the reason that the Dioptrics was already printed in the last months of 1636 and could be sent to France in the first week of 1637, together perhaps with a small part of the Discourse. The unexpected result was that the Dioptrics started to circulate among French mathematicians, especially Pierre de Fermat, to whom the censor, Jean de Beaugrand, had passed a copy, and later Gilles Personne de Roberval. Although at first Descartes humored Mersenne on his attempts to organize this discussion, he became annoyed when Fermat and Roberval remained unconvinced and reacted in ways he did not like. He was also increasingly irritated by the fact the privilège did not come. There were several complications: 1) Descartes wanted a privilège not only for this particular book but for any book he would publish later; 2) Descartes wished that the privilège be given in such a way that his name would not be revealed to the public; 3) the privilège could be granted only on the basis of a complete text. Since printing had been going on after the Dioptrics was sent to Paris, this condition could be fulfilled in March 1637. The privilege was granted finally on May 4, 1637. Descartes was informed of it by Huygens in a letter of June 2, after he had again complained about its failure to appear in a letter of May 20. Apparently, it was sent directly to the printer, as Descartes had asked Mersenne to do. For the publisher this was the signal to have the title page and the pages containing the privileges printed (the achevé d’imprimer is from June 8). In June Descartes started the distribution, sending copies to the stadtholder, the French ambassador, the king of France, and others.
As already pointed out the discussion about the Discourse started even before the book was published. And although Descartes did not particularly like the reactions of Fermat and others to his Dioptrics and in a general way was skeptical about the use of discussion, he encouraged his readers “to take the trouble to send [their objections] to the publisher,” so that they could be published in a second edition, with his replies “so that readers can see both sides together and decide the truth all the more easily” (Discourse VI, AT, vol. VI, p. 75). But only a few people cared to react. Apart from three professors from Louvain, Libertus Fromondus, Vopiscus Fortunatus Plemp, and the Jesuit mathematician Jean Ciermans, Descartes obtained objections only from Jean-Baptiste Morin and from a group of Dutch friends, organized possibly by Alphonse Pollot. Although Descartes was only half satisfied with that result he took the trouble of having all texts copied, possibly to include them in a Latin translation. But although eventually a Latin translation was published, the plan to include objections was shelved definitively on the advice of Huygens.
Plans for a translation on the other hand seem to have been formed as early as 1637. A letter shows not only that a translation of the Essays (and presumably also of the Discourse) was made somewhere in 1639 or even earlier, but also that it was extensively revised by Descartes. Presented as a companion volume to the Principles (1644) the translation of the Discourse, the Dioptrics, and the Meteors (the Geometry was left out) was finally published under the title: Specimina philosophiae (1644). The translation is generally attributed to the Remonstrant minister Étienne de Courcelles or Curcellaeus (1586–1659), who also worked as a reader and corrector for Elzevier. An examination of the variants with respect to the French version make it more than likely that it was revised by Descartes.
DISTINCTION, REAL, MODAL, AND RATIONAL. The word distinctio appears in the title of the second edition of the Meditations (1642), in effect correcting the title of the first, which promised but did not deliver a demonstration of the immortality of the soul. Instead Descartes (responding in effect to a point raised by the Second Objections) promises only to show that they are distinct; from this, one may conclude that the alteration of the body, or even its destruction, is not a sufficient cause for the destruction of the soul (Second Replies, AT, vol. VII, p. 153). In the Fourth Objections, Antoine Arnauld introduces the Scotist terminology of formal and real distinctions, holding that Descartes has not managed to prove that mind and body are really distinct.
The terminology of distinctions is inherited from medieval logic. The first and most fundamental division is between those distinctions that have some foundation in things, and those that do not, but are entirely creatures of our conception. A distinction of reason is a distinction between ways of conceiving the same thing: for Descartes, a body and its quantity or extension are one and the same thing conceived in two ways. The primary instance of a distinction of reason is the distinction between a substance and its essence or nature, which Descartes calls its “principal attribute” (Principles I, art. 62, AT, vol. VIIIA, p. 30). Among those distinctions that have some foundation in things, Descartes recognizes a real and a modal distinction. A real distinction in the primary sense holds between two substances—more precisely, between two things each of which is self-subsistent; from that it follows that each can subsist without the other. A modal distinction holds between two things such that the first can subsist without the second, but not the second without the first. The primary instance is the distinction between a substance (or the principal attribute from which it is distinct only in reason) and any of its nonprincipal modes; the figure of a cube cannot subsist if the substance or quantity of the cube is annihilated, but that quantity can certainly subsist with a new figure.
Descartes distinguishes between the ontological basis of distinctions and their epistemology: we recognize that mind and body are really distinct by virtue of having a “complete idea” of each, an idea by virtue of which we understand that a thinking thing (that is, a thing to which we attribute only thought and its modes) can subsist independently of all things save God, and likewise an idea of body by virtue of which we understand that an extended thing can subsist independently of all things save God; and, finally by virtue of understanding that in the idea of mind there is nothing that pertains to body and in that of body nothing that pertains to mind. Similarly we recognize that a mere distinction of reason exists between a body and its duration by virtue of noting that we cannot clearly and distinctly perceive either without the other (Principles I, art. 62, AT, VIIIA, p. 30).
Divine power is invoked as the cause, in a certain sense, of a real distinction rather than as its basis in things: God, it is said, can bring about whatever we clearly and distinctly perceive, or—in Descartes’s most careful formulation—whatever we conceive “as complete” (Fourth Replies, AT, vol. VII, p. 221). In other words, we can be certain that such-and-such a situation is within God’s power to realize if (and only if) we clearly and distinctly perceive the things in that situation: mind existing while the body is annihilated, for example. Modal truths (“it is possible that my mind should exist without my body”) are grounded in the creative act of God; our thought cannot set limits to divine power, but our clear and distinct ideas can, by virtue of the warrant provided by God’s veracity for our faculties when they are used correctly, enable us to discover some of those truths once they and we have been created.
DIVISIBILITY. According to Descartes, the essence of body is extension. This carries the consequence, clearly indicated in the Sixth Meditation, that every body is divisible: “there is no corporeal or extended thing I can think of which I cannot easily divide into parts in my thought; and this very fact makes me understand that it is divisible” (AT, vol. VII, p. 86). The divisibility of extension is part of the basis of the real distinction between mind and body—the mind is by nature a thinking, unextended thing, while nature of body entails that it is extended and divisible. A further consequence of the fact that every body is divisible is that there can be no atoms or indivisible least parts of extension. This consequence is drawn in the Principles of Philosophy: “if indeed there were [atoms], they would necessarily be extended, no matter how small we might imagine them to be, and hence we could divide each of them in our thought into two or more smaller parts, and thus know that they are divisible” (Principles II, art. 20). This denial of atoms makes the structure of the physical bodies mirror that of geometric magnitudes; just as the lines, angles, or surfaces of pure geometry are always divisible into smaller magnitudes of the same kind, every Cartesian body is divisible into smaller extended bodies.
This raises some conceptual puzzles in the foundation of Descartes’s physics. In particular, it seems to make traditional paradoxes of the infinite divisibility of geometric continua apply to the minute particles that constitute Cartesian matter. Such paradoxes reason that, if every part of a geometric magnitude contains an infinity of lesser parts, then every magnitude is infinitely large or contains a half which is equal to its whole. Descartes emphasized that it was only the indefinite division of matter that was an issue, but he admitted that “the mind does not comprehend . . . the division of any particle of matter infinitely or indefinitely, and in so many parts that however small we make a particle in our thought, we always understand that it is in fact divided into still smaller particles” (Principles II, art. 34). This inability is merely a consequence of our minds’ being finite, however, and takes nothing away from the clarity and distinctness of the principle that every body is divisible into smaller bodies.
DOUBT. According to the Rules for the Direction of the Mind doubt is the opposite of science (or knowledge): “All knowledge is certain and evident cognition. Someone who has doubts about many things is no wiser than one who has never given them a thought; indeed he appears less wise if he has formed a false opinion about any of them. Hence it is better never to study at all than to occupy ourselves with objects which are so difficult that we are unable to distinguish what is true from what is false and are forced to take the doubtful as certain” (Rules II, AT, vol. X, p. 362). That is also the point of the first rule of the method: “never to accept anything as true if I did not have evident knowledge of its truth: that is, carefully to avoid precipitate conclusions and preconceptions, and to include no more in my judgments than what presented itself to my mind so clearly and so distinctly that I had no occasion to doubt it” (Discourse II, AT, vol. VI, p. 18). Meanwhile the reason why something is doubtful has changed or at least has got a different accent.
In the Rules doubt is the result of a lack of method and order (some things are too difficult not to be doubtful if they are not approached in the right order), whereas in the Discourse doubt is the result of prejudice and hasty reasoning. In any case we should try and become free from doubt, even if Descartes makes it clear frequently that in practical matters we should not expect the certainty we are entitled to ask for in the domain of theoretical science. This field, where we are dealing with probability, pertains to the will and is ruled by authority and obedience, the senses, the bodily sensations (hunger, thirst), and the passions. Inversely if we use the rule of doubt to achieve certainty we should set apart whatever pertains to practical life and to the public sphere (religion in particular) and decide not to doubt it.
The rule of doubt is applied to theoretical truth in the Discourse, the First Meditation, and the Principles, where Descartes systematically tests his beliefs according to this criterion, after having divided them into two or three different classes: beliefs based on the senses and the imagination (including memory) and beliefs based on the intellect (see enumeration). But the senses are sometimes deceptive; the imagination also produces dreams; and we know of people who are mad and as a result completely mistaken about their own condition. Descartes concludes that the senses and the imagination are doubtful and accordingly that beliefs based on the senses and the imagination (among other things the belief that there is an external world and that we have a material body) may as well be rejected as false. In the Meditations and the Principles doubt also extends to mathematical demonstrations. This particular doubt, which Descartes calls “hyperbolic” or “metaphysical,” is inspired by the idea that we were created by God who, given his infinite power, could have made us in such a way that we are continually deceived. Of course, one could deny the existence of God, but that makes things worse, given the fact that in that case I would be dependent of something that is even less perfect than God. As an alternative Descartes suggests the hypothesis of what he calls an evil genius (genius aliquis malignus, malin génie) who is powerful enough to deceive me whenever I am irresistibly inclined to affirm something as true.
In the Principles a similar argument returns, but formulated in a somewhat different way: we have heard that there is a God, who is powerful enough to deceive us and who, given the fact that in judgments based on the senses we are actually deceived is, apparently, able to deceive us. Accordingly, we should not trust ourselves even in those judgments we believe to be the most certain of all, namely, mathematical demonstrations. As a result, this exercise in doubt, which was meant to separate what is clear from what is unclear, seems to leave us with nothing at all. However, someone who doubts knows at least that he doubts, a point Descartes already makes in the Rules for the Direction of the Mind but which from the Discourse will take the form of the cogito. Accordingly, if systematic doubt is part of a skeptical argument, radical doubt shows that it is self-defeating—that the more I doubt, the more certain it becomes that I think. The main problem of this argument is that, if we do seriously doubt whatever we believe to know, there should be nothing left to remove doubt. For even if I grant that I think and therefore exist I need certain general principles (such as the notion that an effect cannot have more reality than its cause) to go beyond that and to prove that God exists. So either I doubt those principles and am no longer able to prove that God exists or I do not doubt them but then my doubt is not really radical. Descartes solves this problem by relying on what he calls “natural light” (see intuition) but, according to many critics, an appeal to the natural light could be justified only after I know that God cannot deceive me. See also CARTESIAN CIRCLE.
DUALISM. In the 17th century dualists are those, like Zoroastrians or Manichaeans, who believe in a dual ontology of principles of good and evil. That is how Pierre Bayle employs the term in his Historical Dictionary and how Gottfried Wilhelm Leibniz in turn uses it in his Theodicy. In contemporary philosophy, the term refers generally to the view that reality consists of two disparate elements, that there is an unbridgeable gap between two orders of being. Descartes’s real distinction between extended and thinking substance, between passive body and active mind, thus qualifies as substance dualism. Given the gap between Descartes’s two kinds of substances, the problem becomes one of reconciliation: how can those essentially different substances causally interact? How can the mind influence the body, the body influence the mind? Baruch Spinoza’s property dualism of mutually exclusive but parallel attributes, Nicolas Malebranche’s occasionalism, and Leibniz’s pre-established harmony are all taken to be solutions proposed to the problem of interactive dualism. See also UNION OF MIND AND BODY.
DUHAMEL, JEAN († ca. 1734). Not to be confused with Jean-Baptiste Duhamel, this Duhamel was a professor of philosophy at the Collège du Sorbonne-Plessis from 1668 to about 1690 and a confirmed scholastic critic of the new Cartesian philosophy. He was the author of the Réflexions critiques sur le système cartésien de la philosophie de M. Régis (1692), which beyond responding to the particular version of Cartesian metaphysics and physics in Pierre-Sylvain Régis’s Système also repeats criticisms of Descartes’s views on the method of doubt and the cogito in Pierre-Daniel Huet’s Censura (1690). Régis had this latter feature in mind when he protested in a Réponse to Duhamel’s Réflexions that his critic merely repeats old objections that have already been refuted. Duhamel responded to Régis in a further Lettre . . . pour servir de réplique à M. Régis (1699), but this drew no reply from his Cartesian opponent. Duhamel subsequently published his Philosophia universalis (1705), one of the last defenses of traditional Aristotelianism against the new Cartesian philosophy. This text includes an appendix that records various censures that go back to the Condemnation of 1277 of positions found in Descartes.
DUHAMEL, JEAN-BAPTISTE (1623–1706). Duhamel entered the Oratorians in 1643 and left in 1653 to become the curé of Neuilly-sur-Marne, near Paris. He held further prominent church and academic positions, such as royal almoner, prior of Saint-Lambert, and chair of Greek and Latin Philosophy at the Collège Royal (1682–1704). Duhamel was the first secretary of the Académie Royale des Sciences. He is best known for his attempt to reconcile ancient and modern philosophy. For example, he wrote Astronomia physica and De meteoris et fossilibus (both 1660) as conversations among three persons—Theophilus, the advocate of ancient philosophy, Menander, a passionate Cartesian, and Simplicius, a philosopher indifferent between ancients and moderns, who takes what is best from each (representing Duhamel’s own position). Duhamel also wrote De consensu veteris et novae philosophiae (1663) and Philosophia vetus et nova ad usum scholae accomodata (1678) in this same vein.
DURATION. See CONSERVATION; TIME.
DU ROURE, JACQUES (fl. 1654–83). One of the first followers of Descartes, belonging to the group centering on his literary executor Claude Clerselier. Du Roure is the first to have published a complete textbook of Cartesian philosophy, La Philosophie divisée en toutes ses parties (1654), and subsequently Abrégé de la vraye philosophie (1665), before the more famous ones of Antoine Le Grand and Pierre-Sylvain Régis. In Du Roure’s case, the parts of philosophy include the usual parts of the curriculum—metaphysics, logic, ethics, and physics—plus natural theology. Thus, Du Roure is the first to have written a Cartesian logic or ethics. He also published popular essays, some about Latin language and grammar. Of particular interest is his Dessein d’une institution universelle, inspired by Francis Bacon’s Advancement of Learning. In the section on philosophy as a whole, Du Roure recommends reading scholastics such as Eustachius a Sancto Paulo, but says that he “could set aside some of these, as he has set aside others, because they have given us only trifles” and because he “has never or almost never noticed any demonstrations or experiments in their works, only interminable disputes and a confusion of speech beyond anything that can be imagined” (p. 5). He adds, “whoever wants to become attached to truth in philosophy, rather than to sects, must read the works of Descartes, Gassendi, Hobbes, Kepler, Galileo, Bacon,” among others (p. 6).