“…no matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans are white.”

—  Karl Popper , book The Logic of Scientific Discovery

The Logic of Scientific Discovery (1934)

Adopted from Wikiquote. Last update Nov. 18, 2022. History

Help us to complete the source, original and additional information

Do you have more details about the quote "…no matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans …" by Karl Popper?
Karl Popper photo
Karl Popper 82
Austrian-British philosopher of science 1902–1994

Related quotes

“Establishing by observation that there is just one black swan falsifies "all swans are white". This is an unexceptional and undeniable point. However, using it as grounds to support a falsificationist philosophy of science is not as straightforward as it might seem.”

Alan Chalmers book What Is This Thing Called Science?

Source: What Is This Thing Called Science? (Third Edition; 1999), Chapter 7, The limitations of falsificationism, p. 87.

Giovanni Boccaccio photo

“Charming ladies, the beauty of a flock of white doves is better enhanced by a black crow than by a pure white swan.”

Giovanni Boccaccio book The Decameron

Leggiadre donne, infra molte bianche colombe aggiugne più di bellezza uno nero corvo, che non farebbe un candido cigno.
Ninth Day, Tenth Story
The Decameron (c. 1350)

Karl Popper photo

“… The answer to this problem is: as implied by Hume, we certainly are not justified in reasoning from an instance to the truth of the corresponding law. But to this negative result a second result, equally negative, may be added: we are justified in reasoning from a counterinstance to the falsity of the corresponding universal law (that is, of any law of which it is a counterinstance). Or in other words, from a purely logical point of view, the acceptance of one counterinstance to 'All swans are white' implies the falsity of the law 'All swans are white' - that law, that is, whose counterinstance we accepted. Induction is logically invalid; but refutation or falsification is a logically valid way of arguing from a single counterinstance to - or, rather, against - the corresponding law. This shows that I continue to agree with Hume's negative logical result; but I extend it. This logical situation is completely independent of any question of whether we would, in practice, accept a single counterinstance - for example, a solitary black swan - in refutation of a so far highly successful law. I do not suggest that we would necessarily be so easily satisfied; we might well suspect that the black specimen before us was not a swan.”

Karl Popper book The Logic of Scientific Discovery

Source: The Logic of Scientific Discovery (1934), Ch. 1 "A Survey of Some Fundamental Problems", Section I: The Problem of Induction http://dieoff.org/page126.htm p. 27

Letitia Elizabeth Landon photo

“Yes; for, while memory languidly is fetching
Her treasures from the depths which they have lain among,
A fragile hand — how thin — how weak — is sadly sketching
Figures and fancies that cell's white walls along.
On the lip there is a murmur —
It is the swan's last song.”

Letitia Elizabeth Landon (1802–1838) English poet and novelist

(1838 2) (Vol 53) Subjects for Pictures - The Death of Camoens
The Monthly Magazine

Bertrand Russell photo

“For example, a man who had seen a great many white swans might argue, by our principle, that on the data it was probable that all swans were white, and this might be a perfectly sound argument. The argument is not disproved by the fact that some swans are black, because a thing may very well happen in spite of the fact that some data render it improbable. In the case of the swans, a man might know that colour is a very variable characteristic in many species of animals, and that, therefore, an induction as to colour is peculiarly liable to error. But this knowledge would be a fresh datum, by no means proving that the probability relatively to our previous data had been wrongly estimated. The fact, therefore, that things often fail to fulfill our expectations is no evidence that our expectations will not probably be fulfilled in a given case or a given class of cases. Thus our inductive principle is at any rate not capable of being disproved by an appeal to experience. The inductive principle, however, is equally incapable of being proved by an appeal to experience.”

Bertrand Russell (1872–1970) logician, one of the first analytic philosophers and political activist

"On Induction"
1910s, The Problems of Philosophy (1912)

“And then the heart in its white sailing pride
Launches among the swans and the stretched lights
Laid on the water, as on your cheek
The other kiss and my listening
Life, waiting for all your life to speak.”

Stephen Spender (1909–1995) English poet and man of letters

"Two Kisses"
The Still Centre (1939)

Robert Burton photo

“All our geese are swans.”

Robert Burton book The Anatomy of Melancholy

Section 2, member 3, subsection 14.
The Anatomy of Melancholy (1621), Part I

Epictetus photo

“Were I a nightingale, I would act the part of a nightingale; were I a swan, the part of a swan.”

Epictetus (50–138) philosopher from Ancient Greece

Book I, ch. 16.
Discourses

Benjamin Franklin photo

“Geese are but Geese tho' we may think 'em Swans; and Truth will be Truth tho' it sometimes prove mortifying and distasteful.”

Benjamin Franklin (1706–1790) American author, printer, political theorist, politician, postmaster, scientist, inventor, civic activist, …

"A Dissertation on Liberty and Necessity, Pleasure and Pain" (1725) https://thefederalistpapers.org/founders/franklin/benjamin-franklin-mankind-naturally-and-generally-love-to-be-flatterdm.
Context: Mankind naturally and generally love to be flatter'd: Whatever sooths our Pride, and tends to exalt our Species above the rest of the Creation, we are pleas'd with and easily believe, when ungrateful Truths shall be with the utmost Indignation rejected. "What! bring ourselves down to an Equality with the Beasts of the Field! with the meanest part of the Creation! 'Tis insufferable!" But, (to use a Piece of common Sense) our Geese are but Geese tho' we may think 'em Swans; and Truth will be Truth tho' it sometimes prove mortifying and distasteful.

Related topics