Physical and metaphysical modality

I'm going to explore the idea that what we philosophers mean by " metaphysical necessity " – or, at any rate, what it's best for us to mean – is simply physical necessity. A bit more exactly: We should identify metaphysical necessity with the species of necessity we invoke (usually implicitly) when we try to explain stuff. Along the way, I'll try to show how this thesis connects to a lively contemporary debate between Humeans and anti-Humeans about laws of nature, and try to bring out the variety of distinct forms that physical (or as I'll put it: explanatory) necessity takes. It will also emerge, naturally, that conceivability isn't in any particularly interesting sense a guide to metaphysical possibility. (Maybe that's a feature, maybe it's a bug….)