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An Update Semantics for Promises and Other Obligation-Creating Speech Acts

This thesis is concerned with developing an update semantics to model the speech act of promising, under various philosophical frameworks. There are two main families of promissory framework, conventional and expectational, we offer a hybrid account which makes up for the deficiencies found with both. We also discuss promises in relation to other obligation-creating speech acts to derive a set of desiderata for the formalization. Promises are speech acts which have specific illocutionary and perlocutionary effects which directly map to the deontic and doxastic changes that occur to agents after a promise is successfully made. Update Semantics is a formal framework with the slogan “You know the meaning of a sentence if you know the conditions under which it is true”. The presented approach, Promissory Update Semantics (PUS) extends this to a multi-agent, doxastic, and deontic setting, in the style of Dynamic Epistemic Logic. A series of promissory puzzles, which exemplify the differences between the promissory frameworks, are formalised and discussed in this dynamic setting.