Full Idea
Intransitive relations are introduced into modal semantics for the purposes of interpreting various 'real' or restricted types of modalities, such as nomological necessity.
Gist of Idea
Nomological necessity is expressed with intransitive relations in modal semantics
Source
Nathan Salmon (The Logic of What Might Have Been [1989], II)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.133
A Reaction
The point here is that the (so-called) 'laws of nature' are held to change from world to world, so necessity in one could peter out in some more remote world, rather than being carried over everywhere. A very Humean view of such things.