René Descartes

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

René Descartes (1596-03-311650-02-11) was a highly influential French philosopher, mathematician, scientist, and writer. He has been dubbed the "Father of Modern Philosophy" and the "Father of Modern Mathematics." He is also known as Cartesius.


  • Cogito, ergo sum.
    • Translation: I think, therefore I am.
    • Variant: I think therefore I exist.
    • Principia philosophiae (Principles of Philosophy) (1644)
  • Ex nihilo nihil fit.
    • Translation: Nothing comes out of nothing.
    • Principia philosophiae
  • 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.
    • Translation: Staying as I am, one foot in one country and the other in another, I find my condition very happy, in that it is free.
    • Letter to Elisabeth of Bohemia, Princess Palatine (Paris, June/July 1648)
  • If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.

Le Discours de la Méthode (1637)

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.
    • 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 most fairly distributed thing in the world, for each one thinks he is so well-endowed with it that even those who are hardest to satisfy in all other matters are not in the habit of desiring more of it than they already have.
    Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has.
  • It is not enough to have a good mind. The main thing is to use it well.
    • Pt. 1
  • The greatest minds are capable of the greatest vices as well as of the greatest virtues.
    • Pt. 1
  • 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
  • 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
  • Je pense, donc je suis.
    • Translation: I think, therefore I am.
    • Pt. 4
  • 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.


  • larvatus Prodeo
    • translation: I wear a mask
  • Everything is self-evident.
  • The pituitary gland is the seat of the soul.
  • Except our own thoughts, there is nothing absolutely in our power.
  • I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.
  • I am indeed amazed when I consider how weak my mind is and how prone to error.
  • I concluded that I might take as a general rule the principle that all things which we very clearly and obviously conceive are true: only observing, however, that there is some difficulty in rightly determining the objects which we distinctly conceive.
  • I hope that posterity will judge me kindly, not only as to the things which I have explained, but also to those which I have intentionally omitted so as to leave to others the pleasure of discovery.
  • If I found any new truths in the sciences, I can say that they follow from, or depend on, five or six principal problems which I succeeded in solving and which I regard as so many battles where the fortunes of war were on my side.
  • If we possessed a thorough knowledge of all the parts of the seed of any animal (e.g. man), we could from that alone, by reasons entirely mathematical and certain, deduce the whole conformation and figure of each of its members, and, conversely if we knew several peculiarities of this conformation, we would from those deduce the nature of its seed.
  • If you choose not to decide, you still have made a choice.
  • It is a mark of prudence never to trust wholly in those things which have once deceived us.
  • Illusory joy is often worth more than genuine sorrow.
  • In order to improve the mind, we ought less learn than to contemplate.
    • Variant: In order to improve the mind, we ought less to learn, than to contemplate.
  • It is easy to hate and it is difficult to love. This is how the whole scheme of things works. All good things are difficult to achieve; and bad things are very easy to get.
  • It is only prudent never to place complete confidence in that by which we have even once been deceived.
  • De omnibus dubitandum
    • Translation: All is to be doubted
  • Omnia apud me mathematica fiunt.
    • Translation: With me everything turns into mathematics.
  • Perfect numbers like perfect men are very rare.
  • The long concatenations of simple and easy reasoning which geometricians use in achieving their most difficult demonstrations gave me occasion to imagine that all matters which may enter the human mind were interrelated in the same fashion.
  • The reading of all good books is indeed like a conversation with the noblest men of past centuries who were the authors of them, nay a carefully studied conversation, in which they reveal to us none but the best of their thoughts.
    • Variant: The reading of all good books is like a conversation with the finest minds of past centuries.
  • The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.
  • To do is to be.
  • To know what people really think, pay regard to what they do, rather than what they say.
  • Traveling is almost like talking with those of other centuries.
  • When I consider this carefully, I find not a single property which with certainty separates the waking state from the dream. How can you be certain that your whole life is not a dream?
  • When it is not in our power to determine what is true, we ought to follow what is most probable.
    • Variant: When it is not in our power to follow what is true, we ought to follow what is most probable.
  • When writing about transcendental issues, be transcendentally clear.
  • Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.


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

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