The probability of a dart landing on (1,2) in an (x, y) plane is 0, because there are uncountably many points in the plane. But it is not impossible for the dart to land on (1, 2), because (1, 2) is in the set of points in the plane.
My question is whether a Bayesian would have equal credence in the dart landing on (1, 2) and, say, (1, 2, 3), which is not in the plane at all. It is impossible for the dart to land on (1, 2, 3), but it has 0 probability of landing on (1, 2). How should I understand this difference in Bayesian terms? The impossible case seems like it should get credence 0, but what about the 0 probability case? If they get the same credence, then what does the Bayesian say to differentiate between the cases? There does seem to be a relevant probabilistic difference between them.