 The Rule of Conditionalization is commonly endorsed for updating probabilities in response to new information.  It states that an agent with the probability function \(\pr_1\) at time \(t_1\) who learns \(E\) and nothing stronger at time \(t_2\) should obtain her new probability function \(\pr_2\) from her old probability function by conditionalizing on \(E\), i.e. for each proposition \(A\), \(\pr_2(A) = \pr_1(A\mid E)\), where the conditional probability \(\pr(A\mid E)\) is given in terms of the ratio formula: \(\pr(A\mid E) = \pr(A \&amp; E)/\pr(E)\).  There is a Dutch Book (strategy) argument purporting to show that an agent ought to change beliefs by conditionalization, which was constructed by Lewis (1999), but was first reported by Teller (1973).  If an agent violates this rule by adjusting her probabilities such that \(\pr_2(A) \lt \pr_1(A\mid E)\), a bookie can inflict a sure loss by first selling the agent the following three bets: