Falsifiability
Popper's criterion for distinguishing science from non-science: a theory counts as scientific only if it forbids some observable state of affairs and is therefore in principle refutable.
Falsifiability is the criterion Karl Popper proposed in The Logic of Scientific Discovery (1934, English translation 1959) for distinguishing genuinely scientific theories from non-scientific or pseudo-scientific ones. Popper rejected the verificationist criterion of the Vienna Circle: no finite set of confirming observations can establish a universal generalization, and theories that explain everything (Popper's examples included Marxism and Freudian psychoanalysis) explain nothing.
A scientific theory, on Popper's account, is one that forbids certain observable states of affairs and is therefore in principle refutable by experiment. The theory is corroborated by surviving severe attempts to refute it but is never finally verified. Popper's criterion has been enormously influential in the philosophy of science and in the popular self-understanding of scientists, though it has been refined and contested by Kuhn's analysis of paradigm shifts, Lakatos's research programmes, and Feyerabend's methodological pluralism.
Popper's criterion was developed against the verificationism of the Vienna Circle, which held that a sentence is empirically meaningful if and only if it can be verified by observation. Popper's twin objections were that no finite verification can establish a universal generalization (the inductivist problem) and that theories which can absorb any observation through ad hoc adjustment explain nothing (the demarcation problem). Falsifiability addresses both: a scientific theory must forbid certain observable states of affairs and must be vulnerable to refutation by observation.
The most influential refinement came from Imre Lakatos's methodology of scientific research programmes, which complicated Popper's stark falsificationism by acknowledging that scientists do not abandon central theoretical commitments under the first apparent refutation. Lakatos distinguished progressive from degenerating research programmes by whether they predict novel facts. Paul Feyerabend's Against Method (1975) argued that no methodological rule, falsifiability included, has been consistently followed in scientific history — and that this is a feature rather than a bug.
How philosophers have framed falsifiability
| Philosopher | Position |
|---|---|
| Karl Popper | The criterion of demarcation: scientific theories forbid observable states and are refutable. |
| Rudolf Carnap | Verificationism modified into degrees of confirmation; contested Popper's framework. |
| Thomas Kuhn | Anomalies do not falsify in Popper's sense; paradigms persist until crisis triggers replacement. |
| Imre Lakatos | Refined: progressive research programmes predict novel facts; degenerating ones absorb anomalies. |
| Paul Feyerabend | Anything goes: no methodological rule has been consistently followed in scientific history. |
Representative quotes
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Karl Popper
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“All life is problem solving.”
When I speak of reason or rationalism , all I mean is the conviction that we can learn through criticism of our mistakes and errors, especially through criticism by others, and eventually also through self-criticism. A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others — not by simply taking over another's opini
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Rudolf Carnap
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“Philosophy is to be replaced by the logic of science, that is to say, by the logical analysis of the concepts and sentences of the sciences.”
Foreword
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Thomas Kuhn
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“Normal science means research firmly based upon one or more past scientific achievements.”
p. 10
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Imre Lakatos
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“Imre Lakatos (1974) " From Criticism and the Growth of Knowledge ". as cited in: Thora Margareta Bertilsson (2009) Peirce's Theory of Inquiry and Beyond . p. 41.”
Kuhn as does Popper rejects the idea that science grows by accumulation of eternal truths.. But while according to Popper science is ‘revolution in permanence’, and criticism the heart of the scientific enterprise, according to Kuhn revolution is exceptional and, indeed, extra-scientific, and criticism is, in ‘normal’ times, anathema... The clash between Popper and Kuhn is not about a mere technical
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Paul Feyerabend
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“Science is an essentially anarchic enterprise.”
p. 9.
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