Full Idea
My claim is that there are non-transitive explanations of necessities, where what explains is indeed necessary, but what explains the necessity of the explanandum is not the explanation's necessity, but its truth simpliciter.
Clarification
The 'explanandum' is the thing to be explained
Gist of Idea
The explanation of a necessity can be by a truth (which may only happen to be a necessary truth)
Source
Bob Hale (The Source of Necessity [2002], p.311)
Book Reference
-: 'Philosophical Perspectives' [-], p.311
A Reaction
The big idea is to avoid a regress of necessities. The actual truths he proposes are essentialist. An interesting proposal. It might depend on how one views essences (as giving identity, or causal power)