Falsifiability or refutability of an assertion, hypothesis or theory is the logical possibility that it can be contradicted by an observation or the outcome of a physical experiment. That something is "falsifiable" does not mean it is false; rather, that if it is false, then some observation or experiment will produce a reproducible result that is in conflict with it.

For example, the assertion that "all swans are white" is falsifiable, because it is logically possible that a swan can be found which is not white. Not all statements that are falsifiable in principle are falsifiable in practice. For example, "it will be raining here in one million years" is theoretically falsifiable, but not practically so.

The concept was made popular by Karl Popper, who, in his philosophical criticism of the popular positivist view of the scientific method, concluded that a hypothesis, proposition, or theory talks about the observable only if it is falsifiable.

The classical view of the philosophy of science is that it is the goal of science to prove hypotheses like "All swans are white" or to induce them from observational data. Popper argued that this would require the inference of a general rule from a number of individual cases, which is inadmissible in deductive logic. However, if one finds one single black swan, deductive logic admits the conclusion that the statement that all swans are white is false. Falsificationism thus strives for questioning, for falsification, of hypotheses instead of proving them.

Sir Karl Raimund Popper, CH FRSFBA (28 July 1902 – 17 September 1994) was an Austro-Britishphilosopher and professor at the London School of Economics. He is generally regarded as one of the greatest philosophers of science of the 20th century; he also wrote extensively on social and political philosophy.

Popper is known for his attempt to repudiate the classical observationalist/inductivist form of scientific method in favour of empirical falsification. He is also known for his opposition to the classical justificationist account of knowledge which he replaced with critical rationalism, "the first non justificational philosophy of criticism in the history of philosophy". In political discourse, he is known for his vigorous defence of liberal democracy and the principles of social criticism that he came to believe made a flourishing "open society" possible.

Karl Popper was born in Vienna (then in Austria-Hungary) in 1902, to upper middle-class parents. All of Karl Popper's grandparents were Jewish, but the Popper family converted to Lutheranism before Karl was born. Karl's father Simon Siegmund Carl Popper was a lawyer from Bohemia, and mother Jenny Schiff was of Silesian and Hungarian descent. After establishing themselves in Vienna, the Poppers made a rapid social climb in Viennese society: Simon Siegmund Carl became a legal partner^{[clarification needed]} of Vienna's liberal mayor Raimond Grübl and, after his death in 1898, took over the firm (Karl received his middle name from the mayor).