In Nature of Necessity (1974), Plantinga writes:
The distinction between necessary and contingent truth is as easy to recognize as it is difficult to explain to the sceptic's satisfaction. ...we must give examples and hope for the best.
Here he is speaking of so-called metaphysical necessity (even though he himself adopts the alternative label broadly logical necessity).
I'm interested in learning other views on how to make sense of metaphysical necessity. Can we really do no better than rattle off examples? At what point are the examples sufficient? For instance, if all I consider are examples of logical and/or mathematical truths, is that enough to get an idea of what metaphysical necessity is? That seems implausible. On the other hand, Plantinga for one seems to think that at some point no later than 1974, the variety of stock examples considered by philosophers became sufficient to capture a real and unambiguous concept of it. But of course, this doesn't strike me as very convincing, and I wonder if other philosophers take a different tack.
So, this leads me to the following.
Question. Would you guys please point me to some books/articles (other than Plantinga's) where metaphysical necessity is introduced and defended as a legitimate and definite concept?
Basically, I want to know if I'm being too skeptical and should just go ahead and accept Plantinga's approach, or if perhaps there are some trained, competent philosophers who share my skepticism and think we need to do a lot better than just reflecting on a few examples before barrelling off to study what could turn out to be a hopelessly ambiguous or even downright incoherent notion.
Please note that I am not asking for theories of modality. Perhaps we could say instead that I'm asking what it is exactly that theories of (metaphysical) modality seek to explain, and how we can be assured that there really is such a thing in the first place.