 Some epistemologists find Dutch book arguments to be unconvincing either because they disavow any suitable connection between degrees of belief and betting quotients, or they deny that any facts about something so pragmatic as betting could have normative epistemic force. Joyce (1998) attempts to vindicate probabilism by considering the accuracy of degrees of belief. The basic idea here is that a degree of belief function is defective if there exists an alternative degree of belief function that is at least as accurate in each, and strictly more accurate in some, possible world. The accuracy of a degree of belief \(b(A)\) in a proposition \(A\) in a world \(w\) is identified with the distance between \(b(A)\) and the truth value of \(A\) in \(w\), where 1 represents truth and 0 represents falsity. For instance, a degree of belief up to 1 in a true proposition is more accurate, the higher it is — and perfectly accurate if it equals 1. The overall accuracy of a degree of belief function \(b\) in a world \(w\) is then determined by the accuracy of the individual degrees of belief \(b(A)\). Joyce is able to prove that, given some conditions on how to measure distance or inaccuracy, a degree of belief function obeys the probability calculus if and only if there exists no alternative degree of belief function that is at least as accurate in each, and strictly more accurate in some, possible world (the only-if-part is not explicitly mentioned in Joyce 1998, but present in Joyce 2009). Therefore, degrees of belief should obey the probability calculus.