Source: 1850s, An Investigation of the Laws of Thought (1854), p. 42
“… 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.”
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
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Karl Popper 82
Austrian-British philosopher of science 1902–1994Related quotes
Introduction
Idea for a Universal History from a Cosmopolitan Point of View (1784)
Context: Whatever concept one may hold, from a metaphysical point of view, concerning the freedom of the will, certainly its appearances, which are human actions, like every other natural event are determined by universal laws. However obscure their causes, history, which is concerned with narrating these appearances, permits us to hope that if we attend to the play of freedom of the human will in the large, we may be able to discern a regular movement in it, and that what seems complex and chaotic in the single individual may be seen from the standpoint of the human race as a whole to be a steady and progressive though slow evolution of its original endowment.
German orgiginal: Dimensionslose Konstanten in den Naturgesetzen, die vom rein logischen Standpunkt aus ebensogut andere Werte haben können, dürfte es nicht geben.
As quoted in Begegnungen mit Einstein, von Laue, und Planck (1988) by Ilse Rosenthal-Schneider, p. 31, English edition Reality and Scientific Truth : Discussions with Einstein, von Laue, and Planck (1980) by Ilse Rosenthal-Schneider
Attributed in posthumous publications
Introduction to Logic: and to the Methodology of Deductive Sciences. (1941/2013) Tr. Olaf Helmer, pp. 108-110.
Justification By Faith Alone (1738)
Speech https://api.parliament.uk/historic-hansard/commons/1887/mar/28/motion-for-leave-first-reading#column_1656 in the House of Commons (28 March 1887) introducing the Irish Crimes Bill
Chief Secretary for Ireland
1920s, The Reign of Law (1925)