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Home > Dictionary of Science Quotations > Scientist Names Index P > Karl Raimund Popper Quotes > Theory

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Karl Raimund Popper
(28 Jul 1902 - 17 Sep 1994)

Austrian-British philosopher of science remembered for his writings on theory of scientific method.


Karl Raimund Popper Quotes on Theory (11 quotes)

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A principle of induction would be a statement with the help of which we could put inductive inferences into a logically acceptable form. In the eyes of the upholders of inductive logic, a principle of induction is of supreme importance for scientific method: “... this principle”, says Reichenbach, “determines the truth of scientific theories. To eliminate it from science would mean nothing less than to deprive science of the power to decide the truth or falsity of its theories. Without it, clearly, science would no longer have the right to distinguish its theories from the fanciful and arbitrary creations of the poet’s mind.” Now this principle of induction cannot be a purely logical truth like a tautology or an analytic statement. Indeed, if there were such a thing as a purely logical principle of induction, there would be no problem of induction; for in this case, all inductive inferences would have to be regarded as purely logical or tautological transformations, just like inferences in inductive logic. Thus the principle of induction must be a synthetic statement; that is, a statement whose negation is not self-contradictory but logically possible. So the question arises why such a principle should be accepted at all, and how we can justify its acceptance on rational grounds.
— Karl Raimund Popper
…...
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Almost everyone... seems to be quite sure that the differences between the methodologies of history and of the natural sciences are vast. For, we are assured, it is well known that in the natural sciences we start from observation and proceed by induction to theory. And is it not obvious that in history we proceed very differently? Yes, I agree that we proceed very differently. But we do so in the natural sciences as well.
In both we start from myths—from traditional prejudices, beset with error—and from these we proceed by criticism: by the critical elimination of errors. In both the role of evidence is, in the main, to correct our mistakes, our prejudices, our tentative theories—that is, to play a part in the critical discussion, in the elimination of error. By correcting our mistakes, we raise new problems. And in order to solve these problems, we invent conjectures, that is, tentative theories, which we submit to critical discussion, directed towards the elimination of error.
— Karl Raimund Popper
The Myth of the Framework: In Defence of Science and Rationality (1993), 140.
Science quotes on:  |  Conjecture (22)  |  Correction (28)  |  Criticism (52)  |  Difference (208)  |  Discussion (37)  |  Elimination (17)  |  Error (230)  |  Everyone (20)  |  Evidence (157)  |  History (302)  |  Induction (45)  |  Methodology (8)  |  Mistake (107)  |  Myth (43)  |  Natural Science (62)  |  Observation (418)  |  Prejudice (58)  |  Problem (362)  |  Theory (582)  |  Tradition (43)

In point of fact, no conclusive disproof of a theory can ever be produced; for it is always possible to say that the experimental results are not reliable or that the discrepancies which are asserted to exist between the experimental results and the theory are only apparent and that they will disappear with the advance of our understanding. If you insist on strict proof (or strict disproof) in the empirical sciences, you will never benefit from experience, and never learn from it how wrong you are.
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (2002), 28.
Science quotes on:  |  Experiment (543)  |  Proof (192)  |  Result (250)  |  Theory (582)

It is easy to obtain confirmations, or verifications, for nearly every theory—if we look for confirmations. Confirmations should count only if they are the result of risky predictions... A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice. Every genuine test of a theory is an attempt to falsify it, or refute it.
— Karl Raimund Popper
Conjectures and Refutations: The Growth of Scientific Knowledge (1963), 36.
Science quotes on:  |  Attempt (94)  |  Conception (63)  |  Confirmation (15)  |  Ease (29)  |  Event (97)  |  Falsification (7)  |  Genuine (19)  |  Non-Scientific (4)  |  Prediction (67)  |  Refutation (10)  |  Result (250)  |  Risk (29)  |  Test (96)  |  Theory (582)  |  Verification (20)  |  Vice (15)  |  Virtue (55)

Propose theories which can be criticized. Think about possible decisive falsifying experiments—crucial experiments. But do not give up your theories too easily—not, at any rate, before you have critically examined your criticism.
— Karl Raimund Popper
'The Problem of Demarcation' (1974). Collected in David Miller (ed.) Popper Selections (1985), 126-127.
Science quotes on:  |  Criticism (52)  |  Decisive (9)  |  Ease (29)  |  Examination (60)  |  Experiment (543)  |  Falsification (7)  |  Proposition (47)  |  Theory (582)  |  Thinking (222)

The difficulties connected with my criterion of demarcation (D) are important, but must not be exaggerated. It is vague, since it is a methodological rule, and since the demarcation between science and nonscience is vague. But it is more than sharp enough to make a distinction between many physical theories on the one hand, and metaphysical theories, such as psychoanalysis, or Marxism (in its present form), on the other. This is, of course, one of my main theses; and nobody who has not understood it can be said to have understood my theory.
The situation with Marxism is, incidentally, very different from that with psychoanalysis. Marxism was once a scientific theory: it predicted that capitalism would lead to increasing misery and, through a more or less mild revolution, to socialism; it predicted that this would happen first in the technically highest developed countries; and it predicted that the technical evolution of the 'means of production' would lead to social, political, and ideological developments, rather than the other way round.
But the (so-called) socialist revolution came first in one of the technically backward countries. And instead of the means of production producing a new ideology, it was Lenin's and Stalin's ideology that Russia must push forward with its industrialization ('Socialism is dictatorship of the proletariat plus electrification') which promoted the new development of the means of production.
Thus one might say that Marxism was once a science, but one which was refuted by some of the facts which happened to clash with its predictions (I have here mentioned just a few of these facts).
However, Marxism is no longer a science; for it broke the methodological rule that we must accept falsification, and it immunized itself against the most blatant refutations of its predictions. Ever since then, it can be described only as nonscience—as a metaphysical dream, if you like, married to a cruel reality.
Psychoanalysis is a very different case. It is an interesting psychological metaphysics (and no doubt there is some truth in it, as there is so often in metaphysical ideas), but it never was a science. There may be lots of people who are Freudian or Adlerian cases: Freud himself was clearly a Freudian case, and Adler an Adlerian case. But what prevents their theories from being scientific in the sense here described is, very simply, that they do not exclude any physically possible human behaviour. Whatever anybody may do is, in principle, explicable in Freudian or Adlerian terms. (Adler's break with Freud was more Adlerian than Freudian, but Freud never looked on it as a refutation of his theory.)
The point is very clear. Neither Freud nor Adler excludes any particular person's acting in any particular way, whatever the outward circumstances. Whether a man sacrificed his life to rescue a drowning, child (a case of sublimation) or whether he murdered the child by drowning him (a case of repression) could not possibly be predicted or excluded by Freud's theory; the theory was compatible with everything that could happen—even without any special immunization treatment.
Thus while Marxism became non-scientific by its adoption of an immunizing strategy, psychoanalysis was immune to start with, and remained so. In contrast, most physical theories are pretty free of immunizing tactics and highly falsifiable to start with. As a rule, they exclude an infinity of conceivable possibilities.
— Karl Raimund Popper
'The Problem of Demarcation' (1974). Collected in David Miller (ed.) Popper Selections (1985), 127-128.
Science quotes on:  |  Alfred Adler (3)  |  Falsification (7)  |  Sigmund Freud (66)  |  Marxism (3)  |  Metaphysics (30)  |  Methodology (8)  |  Psychoanalysis (37)  |  Refutation (10)  |  Theory (582)  |  Truth (750)

The empirical basis of objective science has nothing “absolute” about it. Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or “given” base; and when we cease our attempts to drive our piles into a deeper layer, it is not because we have reached firm ground. We simply stop when we are satisfied that they are firm enough to carry the structure, at least for the time being.
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 94.
Science quotes on:  |  Science (1699)  |  Theory (582)

The initial stage, the act of conceiving or inventing a theory, seems to me neither to call for logical analysis nor to be susceptible of it. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (2002), 7.
Science quotes on:  |  Theory (582)

The method of science depends on our attempts to describe the world with simple theories: theories that are complex may become untestable, even if they happen to be true. Science may be described as the art of systematic over-simplification—the art of discerning what we may with advantage omit.
— Karl Raimund Popper
Karl Raimund Popper and William Warren Bartley (ed.), The Open Universe: an Argument for Indeterminism (1991), 44. by Karl Raimund Popper, William Warren Bartley - Science - 1991
Science quotes on:  |  Complexity (80)  |  Description (72)  |  Discern (7)  |  Omit (4)  |  Scientific Method (155)  |  Simplicity (126)  |  Test (96)  |  Theory (582)  |  Truth (750)

The old scientific ideal of episteme — of absolutely certain, demonstrable knowledge — has proved to be an idol. The demand for scientific objectivity makes it inevitable that every scientific statement must remain tentative for ever. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (2002), 280.
Science quotes on:  |  Certainty (97)  |  Proof (192)  |  Theory (582)

Understanding a theory has, indeed, much in common with understanding a human personality. We may know or understand a man's system of dispositions pretty well; that is to say, we may be able to predict how he would act in a number of different situations. But since there are infinitely many possible situations, of infinite variety, a full understanding of a man's dispositions does not seem to be possible.
— Karl Raimund Popper
Objective Knowledge: an Evolutionary Approach (1972), 299.
Science quotes on:  |  Action (151)  |  Disposition (14)  |  Human (445)  |  Infinity (59)  |  Personality (40)  |  Possibility (96)  |  Prediction (67)  |  Situation (41)  |  Solution (168)  |  Theory (582)  |  Understanding (317)  |  Variety (53)


See also:
  • 28 Jul - short biography, births, deaths and events on date of Popper's birth.

Carl Sagan Thumbnail In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) -- Carl Sagan
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