Full Idea
The central characteristic mark of metaphysical necessity is that a metaphysical possibility respects the actual identities of things - in a capacious sense of 'thing'.
Gist of Idea
Metaphysical modalities respect the actual identities of things
Source
Ian Rumfitt (The Boundary Stones of Thought [2015], 3.4)
Book Reference
Rumfitt,Ian: 'The Boundary Stones of Thought' [OUP 2015], p.83
A Reaction
He contrast this with logical necessity, and concludes that some truths are metaphysically but not logically necessary, such as 'Hesperus is identical with Phosphorus'. Personally I like the idea of a 'necessity-maker', so that fits.