 The frameworks we introduce in this section deal chiefly with belief attitudes of the all-or-nothing variety. Most of these represent an agent’s belief state at any particular time by the set of all sentences that she fully believes. All of the frameworks will require that, as a matter of rationality, belief states must be deductively closed and not entail any contradictions. If that were the end of the story, these frameworks would not be very interesting. The real insight of these frameworks is that an agent’s belief state is not adequately represented by a complete list of her current beliefs, but only by her dispositions to update those beliefs upon acquiring new information. Thus, the focus of these frameworks is developing normative principles governing the dynamics of belief states as new information is assimilated. As we shall see, although these frameworks largely agree on the static principles of rationality, they conflict over the dynamical principles of belief update.