Karl Popper and falsification

In short: According to Karl Popper, a scientific theory is characterised by the fact that it can fail when tested against experience. It must be formulated in such a way that one can say which observation would refute it.

In more detail: Popper developed this idea in his book “The Logic of Scientific Discovery” (“Logik der Forschung”), first published in German in the 1930s. His position is known as critical rationalism and strongly shaped 20th-century philosophy of science.

In detail

• The swan example: However many white swans you see, they do not prove that all swans are white, but a single black swan refutes the claim.
• Asymmetry: General laws can never be conclusively confirmed by observations, but they can be refuted; Popper’s method is built on this.
• Demarcation criterion: Popper uses falsifiability as a mark to distinguish science from non-science such as metaphysics or pseudoscience.
• Bold hypotheses: Good theories take risks and rule out many possible observations; the more they risk, the more they say about the world.
• Corroboration instead of proof: If a theory withstands serious attempts to refute it, it counts as corroborated but remains provisional in principle.
• Criticism of immunisation: Popper warned against theories that can be interpreted so that every conceivable observation fits them, citing among others certain forms of psychoanalysis and Marxism.
• Objections: Critics such as Thomas Kuhn stressed that scientists usually do not abandon a well-established theory because of a single contradicting observation.
• The problem of auxiliary assumptions: An experiment never tests a theory on its own, but always together with assumptions about instruments and conditions, so it can be unclear what exactly has been refuted.
• Everyday relevance: The question “What would have to happen for me to change my mind?” is a helpful test against uncritical thinking (induktionsproblem-hume, erkenntnistheorie-wissen-und-glauben, ockhams-rasiermesser-prinzip).