 A positive account is promised by the next strategy for solving the problem of new theory. It operates with a series of ideas. The first idea is that, typically, a person only considers possibilities that are not jointly exhaustive, and she only has credences conditional on the set C of the considered possibilities—lacking an unconditional credence in C (Shimony 1970; Salmon 1990). This deviates from the standard Bayesian view in allowing two things: credence gaps  (section 3.1),  and primitive conditional credences  (section 3.4).  The second idea is that the set C of the considered possibilities might shrink or expand in time. It might shrink because some of those possibilities are ruled out by new evidence, or it might expand because a new possibility—a new theory—is taken into consideration. The third and last idea is a diachronic norm (sketched by Shimony 1970 and Salmon 1990, developed in detail by Wenmackers &amp; Romeijn 2016):