  When it comes to wholesale arguments against scientific realism, perhaps the most influential until recently was the underdetermination argument, according to which the existence of empirical equivalents to our best scientific theories implies that we should withhold epistemic commitment to them. This is often dismissed by realists as generating doubt about unobservables that is no more worrying than doubting other minds or the external world. They argue that since scientists find ways of choosing between empirically equivalent rivals, philosophers ought not to make too much of merely in-principle possibilities that are irrelevant to scientific practice (see Laudan and Leplin 1991, 1993, and Kukla 1998). (Kyle Stanford (2006) defends an underdetermination argument called ‘the problem of unconceived alternatives’ with reference to the history of science, so perhaps not all underdetermination arguments are a priori and theoretical.)