Full Idea
In so far as ground is regarded as a relation it should be between entities of the same type, and the entities should probably be taken as worldly entities, such as facts, rather than as representational entities, such as propositions.
Gist of Idea
If grounding is a relation it must be between entities of the same type, preferably between facts
Source
Kit Fine (Guide to Ground [2012], 1.02)
Book Reference
'Metaphysical Grounding', ed/tr. Correia,F/Schnieder,B [CUP 2012], p.43
A Reaction
That's more like it (cf. Idea 17280). The consensus of this discussion seems to point to facts as the best relata, for all the vagueness of facts, and the big question of how fine-grained facts should be (and how dependent they are on descriptions).
Related Idea
Idea 17280 Ground is best understood as a sentence operator, rather than a relation between predicates [Fine,K]