According to K. Popper for a theory to be considered scientific it must be able to be tested and conceivably proven false. That means it must make specific predictions whose outcome can be checked against measured reality under acceptable conditions. If the predictions turn out to be wrong then there is a problem with the theory on which the predictions are based. Popper calls this “falsifiable”:
Theory T predicts O as an outcome. However we observe P instead of O. This means that T can be tested (is falsifiable) but the test came back negative and there is a problem with T (depending on how central the prediction O is the observation might prove T flat out wrong).
A few examples of statements (predictions) will clarify the principle of falsifiability:
- The sun revolves around the earth (can and has been proven wrong, is therefore falsifiable)
- In X billion years the sun will expand and swallow the earth (can in principle but not practically be proven wrong, is therefore not falsifiable)
- An invisible bunny helps me overcome difficult situations (cannot be proven wrong, is not falsifiable)
- Climate change will make the weather less stable (cannot be proven wrong because “stable” has no specific meaning, the statement is not falsifiable)