 Non-reductionist views about chance, which take chances to be independent fundamental features of reality, can follow PP. Reductionists, who take the values of chances to be fixed entirely by other features of reality (normally frequencies and symmetries, but chance is typically constrained by them in a quite indirect manner),  are for technical reasons (to do with undermining, see supplement  A.1)  ordinarily forced to adopt NP, and Chance-Analyst, as norms on credence, though in many ordinary cases, NP and PP give very similar recommendations. In either case, both formal principles give content to the intuitively plausible idea that chances should  guide reasonable  credence.[1]