 In thinking about ideal knowledge creation though, we might ask how a Bayesian should update their credences in light of peer disagreement or how a group of Bayesians should aggregate beliefs. Bayes rule gives the rational way an agent should update a prior probabilistic credence in light of evidence to obtain a posterior credence. In general, if evidence appears that is more likely given A than B, a Bayesian will increase their credence that A in fact obtains upon observing that evidence. (So if I have a .9 credence that it is raining, and someone walks in wearing shorts and with perfectly dry hair, my credence in rain should decrease because my observation is more likely to occur on a sunny day than a rainy one.) Why is this approach rational? An individual who does not change credences according to Bayes rule can be Dutch booked—offered a series of bets that they will take, but that are guaranteed to lose money.