 Dynamics in a modal probabilistic setting is generally concerned with simultaneous changes to probabilities in potentially all possible worlds. Intuitively, such a change may be caused by new information that invokes a probabilistic revision at each possible world. The dynamics of subjective probabilities is often modeled using conditional probabilities, such as in Kooi (2003), Baltag and Smets (2008), and van Benthem et al. (2009). The probability of \(E\) conditional on \(F\), written \(P(E\mid F)\), is \(P(E\cap F)/P(F)\). When updating by a set \(F\), a probability distribution \(P\) is replaced by the probability distribution \(P'\), such that \(P'(E)= P(E \mid F)\), so long as \(P(F)\neq 0\). Let us assume for the remainder of this dynamics subsection that every relevant set considered has positive probability.