falsifiability

thumb|upright=1.3|alt=Pair of black swans swimming|Here are two black swans, but even with no black swans, "All swans are white" would still be shown falsifiable by "Here is a black swan"—it would still be a valid observation statement in the empirical language, even if empirically false.

Falsifiability is a standard of evaluation of scientific statements, including theories and hypotheses. A statement is falsifiable if it belongs to a language or logical structure capable of describing an empirical observation that contradicts it. In the case of a theory, it says that, given an initial condition, the theory must theoretically prohibit some observations, that is, it must make formal predictions. It was introduced by the philosopher of science Karl Popper in his book The Logic of Scientific Discovery (1934). Popper emphasized that the contradiction is to be found in the logical structure alone, without having to worry about methodological considerations external to this structure. He proposed falsifiability as the cornerstone solution to both the problem of induction and the problem of demarcation.