The Knowledge Machine: How Irrationality Created Modern Science

by Michael Strevens

Science gathers evidence not to validate theories but to refute them—to rule them out of the running. The job of scientists is to go through the list of all possible theories and to eliminate as many as possible, or, as Popper said, to “falsify” them. Suppose that you have accumulated much evidence and discarded many theories. Of the theories that remain on the list, it is impossible, according to Popper, to say that one is more likely to be true than any of the others: “Scientific theories, if they are not falsified, forever remain . . . conjectures.” No matter how many true predictions a theory has made, you have no more reason to believe it than to believe any of its unfalsified rivals. Let me repeat that. Popper is sometimes said (by the New Oxford American Dictionary, for example) to have claimed that no theory can be proved definitively to be true. But he held a far more radical view than this: he thought that of the theories that have not yet been positively disproved, we have absolutely no reason to believe one rather than another. It is not that even our best theory cannot be definitively proved; it is rather that there is no such thing as a “best theory,” only a “surviving theory,” and all surviving theories are equal.