Sometimes people seem to assume that David Lewis took the notion of law of nature to be (somewhat) vague (which I take to mean that 'x is a law of nature at @' has borderline cases), but does Lewis say that explicitly anywhere? (On the face of it, it would seem to be in contrast with the best system thesis being expressed as a biconditional, but, on the other hand, Lewis seems to concede that strength and simplicity are somewhat vague criteria.) And would any other sophisticated regularity theorist be happy with that?
(Crossposted at Matters of Substance. Please post any comments there. (To keep discussion tidy I have disabled them here))