Karl Popper argued that falsifiability distinguishes science from pseudo-science. A theory is scientific if evidence could, in principle, show it to be false; a theory that is compatible with every possible observation is not genuinely testable.
Popper's Demarcation Criterion
Popper called falsifiability a demarcation criterion: a standard for separating empirical science from non-science. Scientific theories make precise, testable claims that prohibit certain outcomes. If one of those prohibited outcomes occurs under appropriate testing conditions, the theory is falsified.
For example, the claim “all swans are white” is falsifiable because observing one genuine black swan would contradict it. Scientists cannot verify the universal claim by observing any finite number of white swans, but they can potentially falsify it through a counterexample. This reflects Popper's criticism of induction: repeated confirming observations cannot logically prove a universal law.
| Science | Pseudo-science |
|---|---|
| Makes precise, risky predictions | Produces vague claims compatible with almost any outcome |
| Exposes theories to possible refutation | Protects claims from refutation |
| Revises or rejects theories after serious counterevidence | Uses ad hoc hypotheses to explain away counterevidence |
| Seeks severe tests rather than confirmation alone | Emphasizes apparent confirmations |
A theory that survives demanding attempts at falsification is corroborated, not proven true. Scientific knowledge therefore remains provisional and open to revision. Popper regarded Einstein's predictions as scientific because they risked observational failure, whereas he criticized theories such as astrology when their interpretations were adjusted to fit every result.
A common misconception is that a falsified theory was never scientific. In fact, falsifiability concerns whether a claim can be tested, not whether it is correct: a testable theory may be scientific even when evidence later shows that it is false. Likewise, an unfalsifiable claim is not automatically meaningless or false; it simply fails Popper's criterion for empirical science.
Exam Technique
In an IB Philosophy response, define falsifiability, explain risky prediction and corroboration, and apply the criterion to an example. For evaluation, question whether observations are theory-laden or whether auxiliary assumptions make decisive falsification difficult.
