ABSTRACT
Philosophers have disagreed about whether theories that make successful predictions are more believable than theories that merely explain data that have already been discovered. Predictivists believe that theories that make successful predictions have an edge over theories that offer only retrospective explanations of the same data. Nonpredictivists maintain that whether a theory predicts data or explains data retrospectively is irrelevant to the believability of the theory. The purpose of this paper is to report on three psychological experiments designed to determine whether undergraduates behave as predictivists or nonpredictivists when they evaluate theories. Results indicate that subjects behaved as nonpredictivists when one theory predicted a body of data and a second theory was devised later to explain the same data retrospectively. However, subjects behaved as predictivists in the situation in which a theory retreated in the face of anomalous data by adding an auxiliary hypothesis; for instance, theories that predicted data by adding the necessary auxiliary hypotheses before the data came in were more believable than theories that added the auxiliary hypothesis in reaction to the data. These results suggest that cognitive models of theory choice that assume that people are nonpredictivists may require modification.
