Certainty can be defined as either:
- perfect knowledge that has total security from error, or
- a synonym for certitude, the mental state of being without doubt
- 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.
- Charles Caleb Colton, in Lacon: Many Things in Few Words (1820-22, 1866), 314
- 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.
- Erich Fromm, in Man for Himself (1947), Ch. 3
- 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.
- Certainty generally is illusion, and repose is not the destiny of man.
- 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' , 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
- Clive Staples Lewis, in Christian Reflections (1967), 111
- 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.
- William Murray, 1st Earl of Mansfield, reported in Andrew Stuart, Letters to the Right Honorable Lord Mansfield (1773), p. 29.
- The scientist believes in proof without certainty, the bigot in certainty without proof.
- Ashley Montagu, Ashley Montagu (ed.), Science and Creationism (1984), Introduction, 9
- 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.
- Sir Isaac Newton, as quoted in Richard S. Westfall, The Life of Isaac Newton (1994), 256
- What is known for certain is dull.
- Max Ferdinand 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.
- Sir Karl Popper, in In Search of a Better World (1994)
- Not to be absolutely certain is, I think, one of the essential things in rationality.
- 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
- The certainties of one age are the problems of the next.
- Richard Henry Tawney, in Religion and the Rise of Capitalism (1926, 2008), 282