Abstract: When is it justified to infer from the fact that a theory provides a good explanation of phenomena to the truth of the theory used in explanation (i.e. inference to the best explanation)? Bas van Fraassen and Pierre Duhem's instrumentalism, which demands only that good theories should ‘save the phenomena’, precludes such inferences altogether. However, in cases of inference to the most probable cause, the instrumentalist position excludes too much. In fact, although explanation via well-tested causal claims does not justify belief in theoretical laws, it does justify belief in the theoretical entities that figure in those claims (i.e. in ‘entity realism’).

Keywords: Pierre Duhem, entity realism, inference to the best explanation, instrumentalism, save the phenomena,