“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. Any theory which can explain everything explains nothing. A theory that fits all possible observations is not a scientific theory.”
—
Karl Popper
The Logic of Scientific Discovery (1934), originally in German; English translation (1959), Routledge, Ch. 1
Commentary
Popper's falsifiability criterion: a theory is scientific if and only if it can, in principle, be proven false. Unfalsifiable claims (psychoanalysis, Marxism, astrology) may be profound or meaningless, but they are not scientific. This demarcates science from pseudoscience.
Popper argued that science progresses not by confirmation but by falsification: we test theories by attempting to prove them false. If they survive severe testing, we have reason to provisionally accept them. This revolutionized philosophy of science, replacing inductionism (generalizing from observations) with falsificationism (testing through attempted refutation). It remains influential though contested.
Commentary
Popper's falsifiability criterion: a theory is scientific if and only if it can, in principle, be proven false. Unfalsifiable claims (psychoanalysis, Marxism, astrology) may be profound or meaningless, but they are not scientific. This demarcates science from pseudoscience.
Popper argued that science progresses not by confirmation but by falsification: we test theories by attempting to prove them false. If they survive severe testing, we have reason to provisionally accept them. This revolutionized philosophy of science, replacing inductionism (generalizing from observations) with falsificationism (testing through attempted refutation). It remains influential though contested.