 It is commonly held that belief is not just an all-or-nothing matter, but admits of degrees. Sophia may believe that Vienna is the capital of Austria to a greater degree than she believes that Vienna will be sunny tomorrow. If her degrees of belief have numerical–and not just ordinal–structure, she might be twice as sure of the former than the latter. Philosophers sufficiently impressed by examples of this sort orient their activity around the structure of “partial belief” rather than the all-or-nothing variety.