Falsifiability

Falsifiability is the philosopher Karl Popper's proposed criterion for what counts as a scientific claim: a theory is scientific only if it forbids some possible observation, so that a real result could in principle show it false. Popper set this out in his 1934 book Logik der Forschung, translated into English in 1959 as The Logic of Scientific Discovery, aiming it specifically at theories he judged unfalsifiable, including certain readings of Freudian psychoanalysis and Marxist history. It has never settled into an uncontested rule: critics, including Popper's own successor Imre Lakatos, argue that real theories are rarely tested and discarded in isolation the way a strict falsificationist story implies, since an anomalous result can often be blamed on an auxiliary assumption instead, a problem known as the Duhem-Quine thesis; it remains a widely taught first criterion rather than a settled last word on demarcation.