Full Idea
It is held that it is the hallmark of metaphysical necessity is that it is completely unrestricted, the limiting case of restricted necessity, with no restrictions whatever. A proposition is necessary only if it is true in absolutely every world whatever.
Gist of Idea
Metaphysical necessity is said to be unrestricted necessity, true in every world whatsoever
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
This is the standard picture which leads to the claim that S5 modal logic is appropriate for metaphysical necessity, because there are no restrictions on accessibility. Salmon raises objections to this conventional view.