Abstract

If the notion of speech acts is to be taken seriously, it must be possible to treat speech acts as acts. The development of systems of DEL (dynamic epistemic logic) in the last two decades suggests an interesting possibility. These systems are developed on the basis of static epistemic logics by introducing model updating operations to interpret various kinds of speech acts including public announcements as well as private information transmissions as what update epistemic states of agents involved. The methods used in developing DEL can be used to develop logics that deal with a much wider variety of speech acts. For example, in ECL (Eliminative Command Logic) of Yamada (2007a) and ECL II of Yamada (2007b), similar model updating operations are introduced tointerpret acts of commanding as what update deontic aspects of the situations in which agents are involved. In Yamada (2008a), ECL II is further extended so as to model acts of promising along with acts of commanding. Moreover, in Yamada (2008b), ECL II is combined with a modified version of DEUL (dynamic epistemic upgrade logic) introduced in van Benthem & Liu (2007). In the resulting logic DDPL (dynamic deontic preference logic), illocutionary acts of commanding are differentiated from preference upgrading perlocutionary acts. The development of these logics suggests a recipe for developing logics that deal with various specific speech acts: first, carefully identify the aspects affected by the speech acts you want to study; second, find the modal logic that characterizes the aspects in question; and finally, add dynamic modalities that stand for the types of the speech acts being studied and define model updating operation that interprets these speech acts as what update the very aspects.