Ebert P & Smith M (2012) Introduction: Outright Belief and Degrees of Belief. Dialectica, 66 (3), pp. 305-308. https://doi.org/10.1111/j.1746-8361.2012.01306.x
First paragraph: We sometimes think of belief as an on-off attitude that we either bear to a proposition or do not. Other times, it seems natural to think of belief as something graded. I believe that I have two hands more strongly than I believe that the average US CEO earns over 200 times as much as the average US worker and, in turn, I believe that the average US CEO earns over 200 times as much as the average US worker more strongly than I believe that Mallory reached the summit of Chomolungma (Mount Everest) in 1924. What considerations like this suggest is that propositions can at least be partially ordered according to the strength of belief that I invest in them. Bayesian epistemologists tend to go further than this, claiming that the strength of belief that I invest in these and other propositions can be associated with real numerical degrees between 0 and 1, with 1 representing certainty of truth, 0 representing certainty of falsehood and 0.5 representing perfect agnosticism. Degrees of belief, so understood, become the basic target of epistemic evaluation for Bayesians, who go on to provide a detailed story as to how they ought to be rationally policed.
Dialectica: Volume 66, Issue 3