 Second, a further complication is that there is an open question whether the various non-causal relations by which metaphysical explanations work must themselves “track” still further relations. For instance, one might maintain that instances of grounding must somehow track the relations of whole to parts, determinable to determinate, role to realizer, set to members, or others. Those with unionist sympathies must therefore be clear about whether grounding explanations are to be identified with grounding or with some non-causal relation that grounding tracks, while separatists must be clear about whether grounding explanations work by tracking grounding, or by tracking some non-causal relation(s) that grounding tracks. Similar points hold for essentialist and reductive explanations, if one holds the view that there are relations that essence-accident and analysans-analysandum must “track”.