Full Idea
The inference from metaphysical necessity to a priori knowlability is, as Kripke has emphasized, fallacious. Indeed, metaphysical necessities cannot be assumed knowable in any way at all.
Gist of Idea
We can't infer metaphysical necessities to be a priori knowable - or indeed knowable in any way
Source
Timothy Williamson (Vagueness [1994], 7.4)
A Reaction
The second sentence sounds like common sense. He cites Goldbach's Conjecture. A nice case of the procedural rule of keeping your ontology firmly separated from your epistemology. How is it? is not How do we know it?
Book Reference
Williamson,Timothy: 'Vagueness' [Routledge 1996], p.203