Sämtliche schriften und briefe series II, volume 1 (2nd edition)
Deutsche Akademie der Wissenschaften (ed)
pp 775-82

Date: 1679

Translated from the French

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[A II 1, p775]


     Since you are happy for me to freely tell you my thoughts on Cartesianism, I will conceal nothing from you of what I think about it and which can be stated succinctly; and I will not put forward anything without giving or being able to give a reason for it.
     Firstly, all those who wholly fall in with the opinions of any author become enslaved, and bring suspicions of error upon themselves; for to say that Descartes is the only author who is exempt from substantial error is a supposition which is possibly true although not probable. Indeed, this attachment belongs only to those who [A II 1, p776] do not have the natural ability or the time to engage in contemplation, or who do not wish to make the effort to do so. This is why the three renowned Academies of our time, England's Royal Society, which was established first, and then the Académie Royale des Sciences in Paris and Accademia del Cimento in Florence,1 have openly declared that they do not wish to be Aristotelians or Epicureans or followers of any author whatsoever.
     Also, experience has taught me that those who are utterly Cartesian are scarcely capable of discovery; they merely take on the role of interpreters of or commentators on their master, as the Scholastic philosophers did with Aristotle. And of the many wonderful discoveries since Descartes, I do not know of any which comes from a true Cartesian. I know these gentlemen a little, and I defy them to name such a discovery from one of their number. This is a sign either that Descartes did not know the true method, or else that he did not bequeath it to them.
     Descartes himself had a rather limited mind. He excelled in speculations over all men, but discovered nothing useful for the life which falls under the senses and which serves in the practice of the arts. All his meditations were either too abstract, such as his metaphysics and geometry, or too fanciful, such as his principles of natural philosophy. The only useful thing he thought he had given were his telescopes made in accordance with the hyperbolic line, with which he promised to show us animals, or parts as small as animals, on the moon.2 Unfortunately, however, he could not find workmen capable of executing his designs, and since then it has been demonstrated that the advantage of the hyperbolic line is not as great as he had thought.
     It is true that Descartes was a great genius and that the sciences are greatly indebted to him, but not in the way the common run of Cartesians believe. I must therefore [A II 1, p777] dip into specifics and give examples of what he took from others, what he did himself, and what he left us to do, whereby it will be clear whether I speak without knowing the facts of the matter. Firstly, his ethics is a blend of Stoic and Epicurean opinions, which wasn't very difficult to achieve since Seneca had already reconciled them very well.3 He wants us to follow reason, or else the nature of things, as the Stoics said, about which everybody will agree. He adds that we should not worry ourselves about things which are not in our power. This is precisely the doctrine of the Portic,4 which established the greatness and freedom of their much-vaunted wise man5 in his strength of mind to bring himself to do without things which do not depend upon us, and to endure them when they happen despite ourselves. This is why I usually term this form of ethics 'the art of patience.' The supreme good, according to the Stoics and Aristotle too, is to act in accordance with virtue or prudence, and the resulting pleasure together with the aforementioned resolution is precisely that tranquillity of the soul or impassibility that the Stoics and Epicureans sought for and also recommended, under different names. One has only to look at the incomparable handbook of Epictetus and the Epicurean Laertius to acknowledge that Descartes did not much advance the practice of ethics.6 But it seems to me that this art of patience, in which he takes the art of living to consist, is still not everything.7 A patience without hope cannot last and is scarcely consoling, and it is in this that Plato, in my view, surpasses the others, as he makes us hope for a better life by means of good arguments, and is closest to Christianity; it is sufficient to read his excellent dialogue on the immortality of the soul, or on the death of Socrates, which Theophile has translated into French, to [A II 1, p778] have a high idea of him.8 9 I think that Pythagoras did the same thing, and that he only used his doctrine of metempsychosis to adapt himself to the capacities of the common man, while among his disciples he reasoned in a completely different way. So Ocellus Lucanus, who was one of his disciples, and from whom we have a small but excellent fragment of his Universe,10 says not one word about it. I will be told that Descartes established the existence of God and the immortality of the soul particularly well. But I fear that we are deceived by fine words, as Descartes' God or perfect being is not God as he is imagined or hoped for, that is, just and wise, doing everything for the good of creatures insofar as it is possible, but rather something similar to Spinoza's God, namely the principle of things and a certain supreme power or primitive nature which sets everything in motion and does everything possible. Descartes' God has neither will nor understanding, since according to Descartes he does not have the good as the object of his will or the true as the object of his understanding. Consequently he does not claim that his God acts in accordance with some end, and this is why he removes the search for final causes from philosophy, under the shrewd pretext that we are incapable of knowing God's ends.11 12 Whereas Plato has shown particularly well that if God is the author of things and acts in accordance with wisdom, then true physics involves knowing the ends and uses of things, since science involves knowing reasons, and the reasons for what has been created by an understanding are the final causes or intentions of the one who created the things.13 These reasons are apparent from the use and function things have, which is why the consideration of the use parts have is so helpful in anatomy. This is why a God like that of Descartes does not permit us any other consolation than that of forced patience. In some passages he says that matter passes successively through all possible forms,14 that is, that his God created everything which is possible and which passes through all possible combinations according to a necessary and inevitable order. But [A II 1, p779] only the necessity of matter would suffice for that, or rather, his God is nothing but this necessity or this principle of necessity acting in matter as it can. Hence it should not be thought that this God has concern for intelligent creatures any more than others; each creature will be happy or unhappy depending on whether it finds itself caught up in these great torrents or tempests, and consequently Descartes is right to recommend to us patience without hope (instead of happiness).
     But an upstanding person among the Cartesian gentlemen, deceived by the fine words of his master, will tell me that Descartes established the immortality of the soul particularly well, and consequently a better life. When I hear things like these I am surprised by how easy it is to deceive people when all one does is shrewdly play around with pleasing words, even if one corrupts their meaning. For just as hypocrites misuse piety, heretics the Scriptures, and seditious people the word 'freedom', Descartes likewise has misused the important words 'the existence of God' and 'the immortality of the soul.' We must therefore clear up this mystery and show them that the immortality of soul according to Descartes is scarcely better than his God. I genuinely think that I will not please some, for people are not happy at being woken up when they are occupied with a pleasant dream. But what else can I do? Descartes wants false thoughts uprooted before introducing true ones.15 We must follow his example; and I believe I will be doing the public a favour if I can disabuse people of such dangerous doctrines.
     I say, then, that the immortality of the soul, such as Descartes establishes it, is useless, and cannot console us in any way. For let us suppose that the soul is a substance and that no substance is completely destroyed; that being so, the soul will not perish, as indeed nothing will perish in nature. But like matter, the soul will also change in a way, and just as the matter which composes a man has at other times composed plants and other animals, this soul will also be able to be immortal in fact, although it will pass through a thousand changes and have no memory of what it was. But this immortality without memory is completely useless for ethics, as it overturns all reward and punishment. What [A II 1, p780] would be the use, Sir, of becoming the King of China on the condition that you forget what you have been? Would this not be the same thing as God creating a King of China at the same time as he destroyed you? This is why, in order to satisfy the hope of humankind, it must be proved that the God who governs all is wise and just, and that he will allow nothing without administering reward and punishment; these are the great foundations of morality. But the doctrine of a God who does not act for the good, and of a soul which is immortal without memory, serves only to deceive simple folk and to corrupt spiritual people.
     Yet I could show the defects in Descartes' so-called demonstration, for there are still many things to prove before it is complete. But I think it is pointless to distract ourselves with this now, since these demonstrations would scarcely be useful even if they were correct, as I have just proved.
     It remains for me to say a little about the other sciences Descartes has dealt with, in order to show examples of what he has done, or of what he has not done. I will begin with geometry, since it is thought that this is Mr Descartes' strength. We must do him justice and say that he was an able geometer, but not so as to outshine the others. He conceals the fact that he had read Viete,16 yet Viete said a great deal, and what Descartes added is, firstly, a more distinct investigation of solid curved lines or curved lines which go through the solid, by means of equations in accordance with loci, and secondly, the method of tangents by two equal roots. Yet in his geometrical works he speaks with an unbearable overconfidence. He boldly says that all problems can be resolved by his method, yet he was obliged to admit on occasion, firstly, that he was unable to solve Diophante's problems of arithmetic, and secondly, that the inverse of tangents surpassed him too. Yet these inverses of tangents comprise the most sublime and most useful part of geometry. I think few Cartesians will understand what I have just said, for there are very few excellent geometers among them; they content themselves with solving some minor problems by the calculations of their master, and two or three great geometers of our times, who are [A II 1, p781] commonly counted among them, recognize the things I have just said only too well to be able to be judged Cartesians.
     Descartes' astronomy is ultimately only that of Copernicus and Kepler, to which he gave a better twist by explaining in a more distinct way the connection of mundane bodies by means of the fluid matter which is pushed by their motion, whereas Kepler, who retained some traces of the School, still made use of some imaginary powers.17 But Kepler had prepared this matter so well that the compromise Mr Descartes made between the corpuscular philosophy and Copernicus's astronomy was not very difficult. I say the same thing about Gilbert's magnetic philosophy,18 and nevertheless I recognize that what Descartes said about the magnet, the ebb and flow of the sea, and meteors, is utterly ingenious, and surpasses everything the ancients said about these things.19 However, I still do not dare to say that he has been completely successful. His Optics has some admirable passages, but it also has some indefensible passages; for example, he succeeded in establishing the proportion between sines but by fumbling around, as the reasons he gave to prove the laws of refraction are worthless.20 I myself think that able geometers now agree about this.
     As for anatomy and the knowledge of man, Descartes is greatly indebted to Harvey, who discovered the circulation of blood, though I do not think he discovered anything which is useful and demonstratively true. He was too preoccupied with reasoning about our body's invisible parts before having properly researched the visible ones. Steno has clearly shown that Descartes was completely mistaken in his opinion about the movement of the heart and muscles.21 And most unfortunately for physics and medicine, Descartes lost his life by believing himself overly able in medicine and by putting off listening to others and accepting treatment when he fell ill in Sweden.22 It must be acknowledged that he was a great man, and if he had lived perhaps he would have looked again at certain errors (if his arrogance would have enabled him to permit it). Most certainly he would have made some important discoveries. But it is also certain that he would not have the reputation he had in his time, in which there were few able people capable of [A II 1, p782] standing up to him, or else were young people only starting out. But since then, things in geometry have been found which Descartes thought impossible, and discoveries have been made in physics which surpass in usefulness all these pleasing fictions of his imaginary vortices. Aside from that, Mr Descartes was ignorant of chemistry, without which it is impossible to advance in applied physics. What he said about salts inspires pity in those who understand the matter, and it is quite clear that he did not know the differences between them.23 If he had had less ambition to form a sect, more patience in reasoning about sensible things, and less inclination to be seduced by the invisible, he would perhaps have laid the foundations of the true physics, for he possessed the admirable genius to succeed in this. But by straying from the true path he damaged his reputation, which will not be as enduring as that of Archimedes, and the fine novel of physics he gave us will soon be forgotten.24 So it is up to posterity to start building on the better foundations which the illustrious Academies are busy laying down in such a way that nothing can shake them. Let us follow their example then; let us contribute to such excellent designs, or else, if we are not suited to discovery, let us at least hold on to the freedom of mind so necessary for being rational.


1. The Royal Society was officially incorporated in 1662 though meetings between founding members were held as far back as 1645; the Accademia del Cimento [Academy of Experiment] was founded in 1657, and the Académie Royale des Sciences [Royal Academy of Sciences] in 1666.
2. See the tenth discourse of Descartes' Optics.
3. For Descartes' ethics, see The Correspondence between Princess Elisabeth of Bohemia and René Descartes, trans. Lisa Shapiro (Chicago: Chicago University Press, 2007).
4. The term 'Portique' ['Portic'] refers to the portico in the agora of ancient Athens which hosted the assemblies of Zeno of Citium (the founder of Stoic philosophy) and his followers. The term is sometimes used to refer either to Zeno himself or to the Stoics as a whole.
5. Zeno of Citium (336-264 B.C.E.).
6. Leibniz is referring to Epictetus, Enchiridion [Handbook], and Diogenes Laertius, De vitis, dogmatis et apophthegmatis clarorum philosophorum libri X [Ten books on the lives and opinions of eminent philosophers], X.
7. everything | , and one thing must be added, which he scarcely considers: it is to be convinced that there is a being which does all things for the general good and for the particular good. The fact is that there must be hope for a better life | deleted.
8. him. | History records, moreover, that there were people who killed themselves after having read this dialogue. | deleted.
9. Leibniz is referring to Plato's Phaedo. As he notes, Theophile de Viau published a French translation - Traicté de l'immortalité de l'âme, ou la mort de Socrate [Treatise on the immortality of the soul, or the death of Socrates] (1619).
10. Ocellus Lucanus, De universi natura libellus [Little book on the nature of the universe] (Venice, 1559).
11. ends | , which in this matter is quite the opposite of Plato's admirable views | deleted.
12. See Descartes, Principles of Philosophy, I.28.
13. Plato, Phaedo, 97b9-98b6.
14. See Descartes' Principles of Philosophy III.47, and his letter to Mersenne of 9 January 1639 in Oeuvres de Descartes, eds. Charles Adam and Paul Tannery (Paris: Vrin), vol. II, p485.
15. An allusion to the first of Descartes' Meditations.
16. See Descartes' letters to Mersenne of 31 March 1638 and 20 February 1639 in Oeuvres de Descartes, op. cit., vol. II, p82 and p524.
17. See Descartes, The World, in The Philosophical Writings of Descartes volume 1, trans. John Cottingham, Robert Stoothoff and Dugald Murdoch (Cambridge: Cambridge University Press, 1985), pp79-108. Also see the third part of Descartes' Principles of Philosophy (various English translations available).
18. William Gilbert, De magnete [On the magnet] (London, 1600).
19. See Descartes, The World, op. cit. Also see the fourth part of Descartes' Principles of Philosophy, and Descartes' Meterology, of which an English translation can be found in Discourse on Method, Optics, Geometry, and Meteorology, trans. Paul J. Olscamp (Indianapolis: Hackett, 2001).
20. See the second discourse of Descartes' Optics, entitled 'Of Refraction.' English translation in Discourse on Method, Optics, Geometry, and Meteorology, op. cit., pp75-83.
21. See Steno's letter to Leibniz of November 1677 in A II 1 (2nd edition), pp576-8, in which Steno claims that his own experiments 'overturned the whole of Mr Descartes' system' relating to the heart (p577). For Descartes on the movement of the heart, see the fifth part of his Discourse on Method.
22. Descartes' biographer, Adrien Baillet, writes of Descartes' final illness in Sweden: '[The fever] was within him the first days, it posses'd his Brain so far, as to make him Rave; took away the liberty of knowing what Condition he was in or hear the advice of his Friends; and deprived him of all strength but only to resist every bodies will... The sick person upon sight of this Doctor [Weulles], and others that the Queen [Christina] sent with him, was so obstinate as to do nothing that he order'd him, but especially he would not hear of being let Blood, all the while the transport of his Brain lasted... His Brain began to be discharged at the end of the 7th day, which made him a little more the Master of his Head, and faculties of his Reason; that was the first time he was sensible of his Feaver: He took notice of the Error he had hitherto laboured under, and now thought of nothing but to dye like a Christian Philosopher. He got himself let Blood twice together, and in a great quantity, but to no purpose, it was then too late.' Adrien Baillet, The Life of Monsieur Des Cartes (London, 1693), pp252-3.
23. See the third discourse of Descartes' Meteorology, entitled 'Of Salt.' English translation in Discourse on Method, Optics, Geometry, and Meteorology, op. cit., pp275-86.
24. This is perhaps an allusion to Descartes' statement in the preface to the Principles of Philosophy that he 'should like the reader first of all to go quickly through the whole book like a novel, without straining his attention too much or stopping at the difficulties which may be encountered.' Descartes, The Philosophical Writings of Descartes I, op. cit., p185.

© Lloyd Strickland 2008