 The immediate challenge to explanationism is to furnish a method with which to identify precisely those aspects of theories that are required for their success, in a way that is objective or principled enough to withstand the charge that realists are merely rationalizing post hoc, identifying the explanatorily crucial parts of past theories with aspects that have been retained in our current best theories. (For discussions, see Chang 2003; Stanford 2003a,b; Elsamahi 2005; Saatsi 2005a; Lyons 2006; Harker 2010; Cordero 2011; Votsis 2011; and Vickers 2013.)