Pierre-Simon Laplace (23 March 1749 – 5 March 1827) was a French mathematician and astronomer, discoverer of the Laplace transform and Laplace's equation.

Pierre-simon Laplace — Translation: "One sees, from this Essay, that the theory of probabilities is basically just common sense reduced to calculus; it makes one appreciate with exactness that which accurate minds feel with a sort of instinct, often without being able to account for it." From the Introduction to Théorie Analytique des Probabilités, second and later editions; also published separately as Essai philosophique sur les Probabilités (1814). Œuvres complètes de Laplace, tome VII, p. cliii, Paris: Gauthier-Villars, 1878-1912. 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." Or as: "Probability theory is nothing but common sense reduced to calculation."

Pierre-simon Laplace — Translation: "The last thing we expect of you, General, is a lesson in geometry!" Laplace to Napoléon, after the latter had reported on some new elementary geometry results^{}

Pierre-simon Laplace — Translation: "What we know is not much. What we do not know is immense." Allegedly his last words, reported in Joseph Fourier's "Éloge historique de M. le Marquis de Laplace" (1829) with the comment, "This was at least the meaning of his last words, which were articulated with difficulty." Quoted in Augustus De Morgan's Budget of Paradoxes (1866).

Pierre-simon Laplace — Translation: "Man follows only phantoms." His true last words, according to Augustus De Morgan's Budget of Paradoxes (1866). Compare Edmund Burke's famous remark, after a parliamentary candidate's sudden death, about "what shadows we are, and what shadows we pursue".

Pierre-simon Laplace — 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.