Certainty can be defined as either:

  1. perfect knowledge that has total security from error, or
  2. a synonym for certitude, the mental state of being without doubt


  • Certainty is the mark of the common-sense life: gracious uncertainty is the mark of the spiritual life. To be certain of God means that we are uncertain in all our ways, we do not know what a day may bring forth. This is generally said with a sigh of sadness, it should be rather an expression of breathless expectation. We are uncertain of the next step, but we are certain of God. Immediately we abandon to God, and do the duty that lies nearest, He packs our life with surprises all the time.
  • No disorders have employed so many quacks, as those that have no cure; and no sciences have exercised so many quills, as those that have no certainty.
  • In this world nothing can be said to be certain, except death and taxes.
    • Benjamin Franklin, Letter to M. Leroy (Nov. 13, 1789). Complete Works, vol. 10, ed. John Bigelow (1887-1888)
  • The quest for certainty blocks the search for meaning. Uncertainty is the very condition to impel man to unfold his powers.
  • Certainty has become a consumer product. It is marketed the world over–by insurance companies, investment advisers, election campaigns, and the medical industry.
  • A common fallacy in much of the adverse criticism to which science is subjected today is that it claims certainty, infallibility and complete emotional objectivity. It would be more nearly true to say that it is based upon wonder, adventure and hope.
  • I believe that we do not know anything for certain, but everything probably.
    • Christiaan Huygens, in a letter to Pierre Perrault, 'Sur la préface de M. Perrault de son traité de l'Origine des fontaines' [1763], Oeuvres Complètes de Christiaan Huygens (1897), Vol. 7, 298. Quoted in Jacques Roger, The Life Sciences in Eighteenth-Century French Thought, ed. Keith R. Benson and trans. Robert Ellrich (1997), 163
We may not be able to get certainty, but we can get probability, and half a loaf is better than no bread. ~ C. S. Lewis
  • We may not be able to get certainty, but we can get probability, and half a loaf is better than no bread.
  • Ah, what a dusty answer gets the soul
    When hot for certainties in this our life!
  • There is no such thing as absolute certainty, but there is assurance sufficient for the purposes of human life.
  • As mathematical and absolute certainty is seldom to be attained in human affairs, reason and public utility require that judges and all mankind in forming their opinions of the truth of facts should be regulated by the superior number of the probabilities on the one side or the other whether the amount of these probabilities be expressed in words and arguments or by figures and numbers.
  • What certainty can there be in a Philosophy which consists in as many Hypotheses as there are Phenomena to be explained. To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty, & leave the rest for others that come after you, than to explain all things by conjecture without making sure of any thing.
  • What is known for certain is dull.
    • Max Perutz, 'My Commonplace Book', in I Wish I'd Made You Angry Earlier (1998), 314
  • Since we can never know anything for sure, it is simply not worth searching for certainty; but it is well worth searching for truth; and we do this chiefly by searching for mistakes, so that we have to correct them.
  • It is said to await certainty is to await eternity.
    • Jonas Salk, Telegram to Basil O'Connor (8 November 1954). In J. S. Smith, Patenting the Sun: Polio and the Salk Vaccine (1990), 295
  • I believe in evil. It is the property of all those who are certain of truth. Despair and fanaticism are only differing manifestations of evil.
    • Edward Teller, as quoted in The Martians of Science : Five Physicists Who Changed the Twentieth Century (2006) by Istvan Hargittai, p. 251
  • Une hypothèse qui permet de prévoir certains effets qui se reproduisent toujours ressemble absolument à une vérité démontrée. Le système de Newton ne repose guère sur un autre fondement. Si en réalité et de l aveu du.
    [A hypothesis which permits the prediction of certain effects that always reoccur under certain conditions does, in its way amount to a demonstrable certainty. Even the Newtonian system had no more than such a foundation.]
    • Alexis de Tocqueville, Letter to de Gobineau (August 5, 1858) Correspondance entre Alexis de Tocqueville et Arthur de Gobineau 1843-1859 (1908) p. 330.
      [Tr. John Lukacs, At the End of an Age (2002)]
Doubt is not a pleasant condition, but certainty is an absurd one. ~ Voltaire
  • Doubt is not a pleasant condition, but certainty is an absurd one.
    • Voltaire, letter to Frederick William, Prince of Prussia (28 November 1770), in S. G. Tallentyre (ed.), Voltaire in His Letters. New York: G. P. Putman's Sons, 1919, p. 232
    • Robert Anton Wilson, in The Illuminatus! Trilogy (1975) (co-written with Robert Shea), Part I : The Eye in the Pyramid p. 176 of 1988 edition
  • If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.

See also

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