 In AGM theory, an agent’s beliefs are represented by a set of sentences \(\bB\) from a formal language \(\mathbf{L}\). The set \(\bB\) is called the belief state of the agent. The belief state is required to be consistent and deductively closed (Hintikka 1961 and the entry on  epistemic logic).  Of course, this is a somewhat unrealistic idealization. Levi (1991) defends this idealization by changing the interpretation of the set \(\bB\)–these are the sentences that the agent is committed to believe, not those that she actually believes. Although we may never live up to our commitments, Levi argues that we are committed to the logical consequences of our beliefs. That may rescue the principle, but only by changing the interpretation of the theory.