One of the central issues to be addressed in basing a theory of speech acts on independently motivated accounts of propositional attitudes (belief, knowledge, intentions, etc.) and action is the specification of the effects of communicative acts. The very fact that speech acts are conventional means that specifying the effects of the utterance of, say, a declarative sentence, or the performance of an assertion, requires taking into consideration many possible deviations from the conventional use of sentences — specifically uses that are insincere, not serious, or indirect. Previous approaches to the problem of specifying speech act consequences have paid insufficient attention to the dependence of the participants’ mental state after an utterance on their mental state preceding it. We present a limited solution to the problem of belief revision within Reiter’s nonmonotonic Default Logic and show how to formulate the consequences of many uses of declarative sentences. Default rules are used to embody a simple theory of belief adoption, action observation, and the relation between the form of a sentence and the attitudes it is used to convey.