 The explanation argument says that grounding is a justified posit because of its explanatory role (Audi 2012a; Dasgupta 2014a; Fine 2012a; Litland 2017; Schaffer 2016a). Recalling the distinction between unionism and separatism (see  §1.1),  the argument proceeds differently depending on which view is in play (Kovacs 2017). Given separatism (grounding is determinationG), one way to cast the explanation argument is as follows: there is a form of explanation—what we can call ontic explanation—such that explanations of this form are backed by worldly relations; and, among the ontic explanations are ones such that the best candidate for the relation that plays the backing role is determinationG. Given unionism (grounding is explanationG), one way to cast the argument is as follows: there is a form of explanation, what we can call metaphysical explanation, such that the connections in metaphysical explanations are best expressed in terms of explanationG.