Pierre-Simon Laplace

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Pierre-Simon Laplace (1749–1827), French mathematician and astronomer, discoverer of the Laplace transform and Laplace's equation.


  • "[Sire,] je n'ai pas eu besoin de cette hypothèse."
    • De Morgan, Augustus (January 1872). Sophia Elizabeth De Morgan ed. A Budget of Paradoxes, London: Longmans, Green, and Co. As found in http://www-history.mcs.st-andrews.ac.uk/~history/Quotations/Laplace.html, accessed February 13, 2006.
    • Translation: "[No, Sire,] I had no need of that hypothesis."
    • Reputed reply to Emperor Napoleon I, who had asked why he hadn't mentioned God in his discourse on secular variations of the orbits of Saturn and Jupiter ("Mais où est Dieu dans tout cela ?").
  • The exchange is reported by Victor Hugo (who in turn was citing Arago) as:
  • "Comment, vous faites tout le système du monde, vous donnez les lois de toute la création et dans tout votre livre vous ne parlez pas une seule fois de l'existence de Dieu !"
    • Translation: "How can this be! You made the system of the world, you explain the laws of all creation, but in all your book you speak not once of the existence of God!"
    • Alternate translation: "You have written this huge book on the system of the world without once mentioning the author of the universe!"
    • Alternate translation: "How is it that, although you say so much about the Universe, you say nothing about its Creator?"
  • "[Sire,] je n'avais pas besoin de cette hypothèse."
  • Lagrange, also present, then commented: "Ah, but that is such a good hypothesis. It explains so many things!"
  • To which Laplace replied: "Indeed, Sire, Monsieur Lagrange has, with his usual sagacity, put his finger on the precise difficulty with the hypothesis: it explains everything, but predicts nothing."

  • "Probability theory is nothing but common sense reduced to calculation."
    • Also reported as:
  • "The theory of probabilities is at bottom nothing but common sense reduced to calculus; it enables us to appreciate with exactness that which accurate minds feel with a sort of instinct for which ofttimes they are unable to account."
  • "Tous les événemens, ceux même qui par leur petitesse, semblent ne pas tenir aux grandes lois de la nature, en sont une suite aussi nécessaire que les révolutions célestes. [...] Mais dans l'ignorance où nous sommes de l'immensité des données nécessaires à la solution de ce grand problème, et dans l'impossibilité, vu notre faiblesse, d'assujétir au calcul la plupart de celles qui nous sont connues [...] nous attribuons les phénomènes [... au] hasard, [...] qui n'est au fond que l'expression de notre ignorance."
    • Translation: "All events, who by their smallness seem not consequences of natural laws, are in fact outcomes as necessary as celestial movements [...] but because of our ignorance of the immense majority of the data required and our inability to submit to computation most of the data we do know of, [...] we attribute these phenomena to randomness, [...] an expression of nothing more than our ignorance."

  • "Les questions les plus importantes de la vie ne sont en effet, pour la plupart, que des problèmes de probabilité."
    • Translation: "Life's most important questions are, for the most part, nothing but probability problems."

  • "La dernière chose que nous attendions de vous, Général, est une leçon de géométrie !"
    • Translation: "The last thing we expected of you, General, was a lesson in geometry!"
    • Laplace to Napoléon, after the latter had reported on some new elementary geometry results

  • "What we know is not much. What we do not know is immense."
    • Allegedly his last words, as quoted in Augustus De Morgan's Budget of Paradoxes (1866).

  • "Man follows only phantoms."
    • His true last words, according to Augustus De Morgan's Budget of Paradoxes (1866).

  • "Lisez Euler, lisez Euler, c'est notre maître à tous."
    • Translation: "Read Euler: he is our master in everything." (Although a more accurate translation would be: "Read Euler, read Euler, he is the master of us all.")
    • Reported by Gugliemo Libri in the Journal des Savants, January 1846, p. 51: « ...ces paroles mémorables que nous avons entendues de sa propre bouche : "Lisez Euler, lisez Euler, c'est notre maître à tous". »

  • "Nature laughs at the difficulties of integration."
    • Quoted in I. Gordon and S. Sorkin, The Armchair Science Reader, New York, 1959.

  • "Il est facile de voir que..."
    • Translation: "It is therefore obvious that..."
    • Frequently used in the Traité de mécanique céleste when he had proved something and mislaid the proof, or found it clumsy. Notorious as a signal for something true, but hard to prove.

See also

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