Problem
According to Popper, why must a theory be falsifiable? Construct an example of a non-falsifiable statement and show why it remains outside science.
Solution
Popper’s criterion. For Karl Popper, what distinguishes a scientific theory from a non-scientific one is falsifiability: a theory is scientific if it forbids something observable, that is, if there exists at least one possible experiment or observation that, were it to occur, would refute it. The reason is that science can never prove a universal law definitively (no number of confirmations proves it forever), but it can refute it with a single counterexample. A theory that forbids certain outcomes is testable: it puts risky predictions at stake. A theory compatible with any result, on the other hand, says nothing verifiable.
Example of a non-falsifiable statement. “There exist invisible spirits that cause fortunate events, but they never leave any detectable physical trace.” Whatever happens is compatible with this statement: if things go well for you, it’s thanks to the spirits; if things go badly, the spirits did not intervene. No observation could ever contradict it, because by construction the spirits produce no measurable effects. Precisely for this reason the statement is not testable and remains outside science: it is neither true nor false in a scientific sense, it simply cannot be put to the test.
Comparison with a scientific statement. “All bodies fall in a vacuum with the same acceleration .” This forbids a precise outcome: it would be enough to observe, in a vacuum, two bodies falling with different accelerations to falsify it. It is risky, testable and therefore fully scientific.
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Topics: Metodo sperimentale