 This issue divides Bayesians. First of all, there is the party of subjective Bayesians, who hold that every prior is permitted unless it fails to be coherent. So, to those Bayesians, the correct norms for priors are exhausted by Probabilism and the other coherence norms if any. Second, there is the party of objective Bayesians, who propose that the correct norms for priors include not just the coherence norms but also a norm that codifies the epistemic virtue of freedom from bias. Those Bayesians think that freedom from bias requires at least that, roughly speaking, one’s credences be evenly distributed to certain possibilities unless there is a reason not to. This norm, known as the Principle of Indifference, has long been a source of controversy. Last but not the least, some Bayesians even propose to take seriously certain epistemic virtues that have been extensively studied in other epistemological traditions, and argue that those virtues need to be codified into norms for priors. For more on those attempted solutions to the problem of the priors, see  section 4  below. Also see  section 3.3 of the entry on interpretations of probability.