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
Discourse on the Method
Meditations on First Philosophy
Principles of Philosophy


  • 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

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!
  • This momentous finding of nonlocality has, in common with that of Einstein concerning time, the additional feature that it disproves the validity, not of a "view of the World", but of a deeply ingrained concept. And this brings me to the second reason. It is that this disproof of a deeply ingrained concept pointed in fact in a direction quite consonant with my own line of thought. In a way, it brings us back to Descartes, for, as we all know, Descartes was the first scientist who dared to question our common views, including even all the notions that had always seemed so primitive and obvious that thinkers, scientists and so on never hesitated in making use of them. He found out that, at the start, he could doubt of everything but his own thinking, and in this, according to Hegel, he was a hero. Unfortunately he then constructed a grand metaphysical argument that led him to the view that, after all, since God is not a liar, the "obvious" realistic concepts must apply. He thereby founded mechanicism, which is the theory that, apart from thought, everything has to be described by the exclusive means of familiar concepts. We know, of course, how deficient such a view is. But I think Descartes' really significant contribution on these matters is not mechanicism. It is what I just said. In other words, it is the realization that a sharp distinction has to be made between rationality on the one hand and the use of seemingly obvious concepts on the other hand. And that therefore, if you are a rational person you cannot demand that science should be based exclusively on seemingly obvious concepts without first logically justifying this demand. This Descartes tried to do but, since his argument based on God not being a liar is now considered as not convincing enough, we are not bound to his conclusion. Indeed, I consider that we are not even bound to the idea that physics should be expressed in an ontological language, which was more or less Einstein's view. The older Einstein seems to have considered that Reality, and even physical objects in the plural, can be described as they really are, if not by familiar concepts, at least by unfamiliar ones, such as those borrowed from mathematics. I do not think this is necessarily true. I consider that mere predictive rules, such as the Born rule in quantum mechanics, count as fully fledged explanations, or, more precisely, as constituting, when all taken together, a first step in an explanation, the second step being the philosophical idea that these predictive rules dimly reflect some existing, largely hidden structures of Mind-Independent Reality. Of course, these speculations of mine go much further than nonlocality. But you understand that they receive some support from it.
    • Bernard d'Espagnat, "My Interaction with John Bell", in Quantum [Un]speakables (2002) edited by R.A. Bertimann, A. Zeilinger
  • 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)
  • There seems to me to exist a sort of rationalism which, by not recognizing these limits of the powers of individual reason, in fact tends to make human reason a less effective instrument than it could be. … This sort of rationalism is a comparatively new phenomenon, though its roots go back to ancient Greek philosophy. Its modern influence, however, begins only in the sixteenth and seventeenth century and particularly whith the formulation of its main tenets by the French philosopher, René Descartes.
    • Friedrich Hayek, "Kinds of Rationalism", The Economic Studies Quarterly (1965)
  • 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.
  • Thus was the Nixon Administration first exposed to the maddening diplomatic style of the North Vietnamese. It would have been impossible to find two societies less intended by fate to understand each other than the Vietnamese and the American. On the one side, Vietnamese history and Communist ideology combined to produce almost morbid suspicion and ferocious self-righteousness. This was compounded by a legacy of Cartesian logic from French colonialism that produced an infuriatingly doctrinaire technique of advocacy.
    • Henry A. Kissinger, The White House Years
  • As a symbol of the power of absolutism, Versailles has no equal. It also expresses, in the most monumental terms of its age, the rationalistic creed—based on scientific advances, such as the physics of Sir Isaac Newton (1642–1727) and the mathematical philosophy of René Descartes (1596–1650)—that all knowledge must be systematic and all science must be the consequence of the intellect imposed on matter. The whole spectacular design of Versailles proudly proclaims the mastery of human intelligence (and the mastery of Louis XIV) over the disorderliness of nature.
    • Fred S. Kleiner, Gardner’s Art through the Ages: A Global History (2009)
  • "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)
  • In the theory of the state of the seventeenth century, the monarch is identified with God and has in the state a position exactly analogous to that attributed to God in the Cartesian system of the world.
  • Descartes may have made a lot of mistakes, but he was right about this: you cannot doubt the existence of your own consciousness. That's the first feature of consciousness, it's real and irreducible. You cannot get rid of it by showing that it's an illusion in a way that you can with other standard illusions.
  • 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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