 Inference to the Best Explanation is the controversial rule of inference which basically holds that, out of the class of potential explanations we have of some phenomena, we should infer that the best explanation is the true one. If Inference to the Best Explanation is a rule we do (or ought) to follow, then it looks as if scientific realism is an accurate description (or prescription) of the aims of science—we should acknowledge the reality of the entities our best explanatory theories postulate, even if those entities are unobservable.