René Descartes

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René Descartes
It is not enough to have a good mind. The main thing is to use it well.

René Descartes (March 31, 1596February 11, 1650) was a highly influential French philosopher, mathematician, physicist and writer. He is known for his influential arguments for substance dualism, where mind and body are considered to have distinct essences, one being characterized by thought, the other by spatial extension. He has been dubbed the "Father of Modern Philosophy" and the "Father of Modern Mathematics." He is also known as Cartesius.

See also: Meditations on First Philosophy


  • On the one hand I have a clear and distinct idea of myself, in so far as I am a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far a this is simply an extended, non-thinking thing. And, accordingly, it is certain that I am really distinct from my body, and exist without it.
  • I do not see how God could be understood to be anything but a deceiver if the ideas were transmitted from a source other than corporeal things. It follows that corporeal things exist. They may not all exist in a way that exactly corresponds with my sensory grasp of them, for in many cases the grasp of the senses is very obscure and confused. But at least they possess all the properties which I clearly and distinctly understand, that is, all those which, viewed in general terms, are comprised within the subject-matter of pure mathematics.
    • Meditations on First Philosophy (1641), tr. John Cottingham, Descartes: Meditations on First Philosophy (1986)
  • Cogito, ergo sum.
    • I think, therefore I am.
    • Variant: I think therefore I exist.
    • Principia philosophiae (Principles of Philosophy) (1644), Part I, Article 7
  • Ex nihilo nihil fit.
    • Nothing comes out of nothing.
    • Principia philosophiae, Part I, Article 49
  • Me tenant comme je suis, un pied dans un pays et l’autre en un autre, je trouve ma condition très heureuse, en ce qu’elle est libre.
  • So blind is the curiosity by which mortals are possessed, that they often conduct their minds along unexplored routes, having no reason to hope for success, but merely being willing to risk the experiment of finding whether the truth they seek lies there.
    • Rules for the Direction of the Mind: IV
  • The entire method consists in the order and arrangement of the things to which the mind’s eye must turn so that we can discover some truth.
    • Rules for the Direction of the Mind: X.379
    • As quoted in Clarke, Desmond M. (2006). Descartes : a Biography. Cambridge Press. p. 67. ISBN 978-0-521-82301-2. 
  • Mais apud me omnia fiunt Mathematicè in Natura
    • Loosely translated: With me, everything turns into mathematics.
    • More closely translated as: but in my opinion, all things in nature occur mathematically.
      • Note: "Mais" is French for "but" and the "but in my opinion" comes from the context of the original conversation. apud me omnia fiunt Mathematicè in Natura is in latin.
    • Sometimes the Latin version is incorrectly quoted as Omnia apud me mathematica fiunt.
    • Sources: Correspondence with Mersenne note for line 7 (1640), page 36, Die Wiener Zeit page 532 (2008); StackExchange Math Q/A Where did Descartes write...

Le Discours de la Méthode (1637)[edit]

Discourse on the Method of Rightly Conducting the Reason, and Seeking Truth in the Sciences
  • Of all things, good sense is the most fairly distributed: everyone thinks he is so well supplied with it that even those who are the hardest to satisfy in every other respect never desire more of it than they already have. (fr; en)
    • Pt. 1
    • Variants:
      • Good sense is of all things in the world the most equally distributed, for everybody thinks he is so well supplied with it, that even those most difficult to please in all other matters never desire more of it than they already possess.
      • Common sense is the best distributed commodity in the world, for every man is convinced that he is well supplied with it.
      • Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has.
  • Car ce n'est pas assez d'avoir l'esprit bon, mais le principal est de l'appliquer bien. [1]
    • Translation: It is not enough to have a good mind. The main thing is to use it well.
    • Pt. 1
  • The greatest minds, as they are capable of the highest excellencies, are open likewise to the greatest aberrations; and those who travel very slowly may yet make far greater progress, provided they keep always to the straight road, than those who, while they run, forsake it.
    • Pt. 1
    • Variants:
      • The greatest minds are capable of the greatest vices as well as of the greatest virtues.
  • The first precept was never to accept a thing as true until I knew it as such without a single doubt.
    • Pt. 2
  • Divide each difficulty into as many parts as is feasible and necessary to resolve it.
    • Pt. 2
  • The last rule was to make enumerations so complete, and reviews so comprehensive, that I should be certain of omitting nothing.
    • Pt. 2
  • The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, to the knowledge of which man is competent, are mutually connected in the same way, and that there is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it, provided only we abstain from accepting the false for the true, and always preserve in our thoughts the order necessary for the deduction of one truth from another.
    • Pt. 2
  • Each problem that I solved became a rule, which served afterwards to solve other problems.
    • Pt. 2
  • On ne sauroit rien imaginer de si étranger et si peu croyable, qu’il n’ait été dit par quelqu’un des philosophes...
    • One cannot conceive anything so strange and so implausible that it has not already been said by one philosopher or another.
    • Variant: There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.
    • Pt. 2
    • Cf. Cicero's "Nihil tam absurde dici potest, quod non dicatur ab aliquo philosophorum [There is nothing so absurd that it has not been said by some philosopher]" (De Divinatione, Book II, chapter LVIII, sec. 119).
  • Je pense, donc je suis.
    • I think, therefore I am.
    • Pt. 4
  • [B]ut if there were machines bearing the image of our bodies, and capable of imitating our actions as far as it is morally possible, there would still remain two most certain tests whereby to know that they were not therefore really men.
    • Pt. 5

Quotes about Descartes[edit]

  • Descartes maintained his confidence in the instantaneity of light. ...Yet in his derivation of the law of refraction, Descartes reasoned that light travelled faster in a dense medium than in one less dense. He seems to have had no qualms about comparing infinite magnitudes!
  • Newton's proof of the law of refraction is based on an erroneous notion that light travels faster in glass than in air, the same error that Descartes had made. This error stems from the fact that both of them thought that light was corpuscular in nature.
    • John Freely, Before Galileo, The Birth of Modern Science in Medieval Europe (2012)
  • Aristotle remarks in his Poetics that poetry is superior to history, because history presents only what has occurred, poetry what could and ought to have occurred, poetry has possibility at its disposal. Possibility, poetic and intellectual, is superior to actuality; the esthetic and the intellectual are disinterested. But there is only one interest, the interest in existing; disinterestedness is the expression for indifference to actuality. The indifference is forgotten in the Cartesian Cogito-ergo sum, which disturbs the disinterestedness of the intellectual and offends speculative thought, as if something else should follow from it. I think, ergo I think; whether I am or it is (in the sense of actuality, where I means a single existing human being and it means a single definite something) is infinitely unimportant. That what I am thinking is in the sense of thinking does not, of course, need any demonstration, nor does it need to be demonstrated by any conclusion, since it is indeed demonstrated. But as soon as I begin to want to make my thinking teleological in relation to something else, interest enters the game. As soon as it is there, the ethical is present and exempts me from further trouble with demonstrating my existence, and since it obliges me to exist, it prevents me from making an ethically deceptive and metaphysically unclear flourish of a conclusion.
  • "There is one basis of science," says Descartes, "one test and rule of truth, namely, that whatever is clearly and distinctly conceived is true." A profound psychological mistake. It is true only of formal logic, wherein the mind never quits the sphere of its first assumptions to pass out into the sphere of real existences; no sooner does the mind pass from the internal order to the external order, than the necessity of verifying the strict correspondence between the two becomes absolute. The Ideal Test must be supplemented by the Real Test, to suit the new conditions of the problem.
  • By... confounding the properties of matter with those of space he arrives at the logical conclusion, that if the matter within a vessel could be entirely removed the space within the vessel would no longer exist. In fact he assumes that all space must be always full of matter.
  • The primary property of matter was indeed distinctly announced by Descartes in what he calls the "First Law of Nature": "That every individual thing, so far as in it lies, perseveres in the same state, whether of motion or of rest."
    • James Clerk Maxwell, Matter and Motion (1876)
  • Descartes... fell back on his original confusion of matter with space—space being, according to him, the only form of substance, and all existing things but affections of space. This error... forms one of the ultimate foundations of the system of Spinoza.
  • I would inquire of reasonable persons whether this principle: Matter is naturally wholly incapable of thought, and this other: I think, therefore I am, are in fact the same in the mind of Descartes, and in that of St. Augustine, who said the same thing twelve hundred years before. ...I am far from affirming that Descartes is not the real author of it, even if he may have learned it only in reading this distinguished saint; for I know how much difference there is between writing a word by chance without making a longer and more extended reflection on it, and perceiving in this word an admirable series of conclusions, which prove the distinction between material and spiritual natures, and making of it a firm and sustained principle of a complete metaphysical system, as Descartes has pretended to do. is on this supposition that I say that this expression is as different in his writings from the saying in others who have said it by chance, as in a man full of life and strength, from a corpse.
  • Descartes subscribed to the doctrine of instantaneous propagation, but with him something new emerged: for his was the first uncompromisingly mechanical theory that asserted the instantaneous propagation of light in a material medium... Indeed, mechanical analogies had been used to explain optical phenomena long before Descartes, but the Cartesian theory was the first clearly to assert that light itself was nothing but a mechanical property of the luminous object and of the transmitting medium. It is for this reason that we may regard Descartes' theory of light as legitimate starting point of modern physical optics.
    • A. I. Sabra, Theories of Light, from Descartes to Newton (1981)
  • Man occupies a special place in the Cartesian scheme. He alone is endowed with mind. Descartes believed that animals did not possess one, that they were simply extremely complicated automatons. Other thinkers have rejected this point of view and proposed to endow all matter in the universe—living or inanimate—with consciousness. This "panpsychism" has been promoted by, among others, Teilhard de Chardin and, more recently by the British-American physicist Freeman Dyson, who holds that mind is present in every particle of matter.
  • The truth is sum, ergo cogito — I am, therefore I think, although not everything that is thinks. Is not consciousness of thinking above all consciousness of being? Is pure thought possible, without consciousness of self, without personality? Can there exist pure knowledge without feeling, without that species of materiality which feelings lends to it? Do we not perhaps feel thought, and do we not feel ourselves in the act of knowing and willing? Could not the man in the stove [Descartes] have said: "I feel, therefore I am"? or "I will, therefore I am"? And to feel oneself, is it not perhaps to feel oneself imperishable?
  • After Bruno's death, during the first half of the seventeenth century, Descartes seemed about to take the leadership of human thought... in promoting an evolution doctrine as regards the mechanical formation of the solar system... but his constant dread of persecution, both from Catholics and Protestants, led him steadily to veil his thoughts and even to suppress them. The execution of Bruno had occurred in his childhood, and in the midst of his career he had watched the Galileo struggle in all its stages. He had seen his own works condemned by university after university under the direction of theologians and placed upon the Roman Index. ...Since Roger Bacon, perhaps, no great thinker had been so completely abased and thwarted by theological oppression.


  • An optimist may see a light where there is none, but why must the pessimist always run to blow it out?
    • Michel de Saint-Pierre, as quoted in Cryptograms and Spygrams (1981) by Norma Gleason, p. 106; attributed to Descartes in The Athlete's Way : Training Your Mind and Body to Experience the Joy of Exercise (2008) by Christopher Bergland, p. 271.
  • Doubt is the origin of wisdom and Latin: Dubium sapientiae initium. This has been attributed to Descartes, including here previously, but no original attribution has been found. Descartes Meditationes de prima philosophia has been cited as the source of Dubium sapientiae initium, but this quote is not found in this work.

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