Plural and singular grounding

Here’s a tempting principle:

1. If x and y ground z, then the fusion of x and y grounds z.

In other words, we don’t need proper pluralities for grounding—their fusions do the job just as well.

But the principle is false. For the principle is only plausible if any two things have a fusion. But if x and y do not overlap, then x and y ground their fusion. And then (1) would say that the fusion grounds itself, which is absurd.

This makes it very plausible to think that plural objectual grounding does not reduce to singular objectual grounding.