Commitments, beliefs and expectations in conversation: Understanding the effect of speech acts in logic
Thomas van der Leer

Abstract:
This thesis departs from the idea that, by performing speech acts, we undertake commitments to act in accordance with their content (Brandom, 1983; Geurts, 2019; Hamblin, 1971; Tuzet, 2006). Three effects that speech acts have on the discourse and its participants will be studied through this lens. First, the commitments speech acts invoke manipulate interlocutors’ normative attitudes, since commitments are social obligations. Second, they affect their beliefs, since after the performance of a speech act discourse participants believe that certain commitments are made and may also come to believe in the content of these commitments. Lastly, the commitments introduced by a speech act shape our expectations regarding the discourse development, given that we prefer to be cooperative by making the same commitments and do not expect someone to violate their commitments by making inconsistent claims. Whereas existing commitment-based theories typically seem to be concerned with either the relation between commitment and belief or between commitment and expectation, the goal of this thesis is to unite all three effects of speech acts in one dynamic logical system. In the Speech Act Logic (SAL) that this thesis introduces, both commitment and belief are defined as modal operators that are updated on the basis of speech act performance. Moreover, by following Commitment Space Semantics (CSS; Cohen & Krifka, 2014; Krifka, 2015) in representing the discourse as a commitment space, SAL captures not only the speech act’s effect on the current state of the discourse but on its projected future states as well. However, whereas CSS models only one type of discourse expectation (similarly to Farkas and Bruce (2010)), SAL is able to represent different layers of expectations, by formally distinguishing between commitment violation and uncooperative behaviour. Although the thesis mainly focuses on discussing and formalising assertions, SAL is applied to polar questions and speech act embeddings as well and could be further extended to a model of yet other speech act types. To motivate the formal work, the thesis will along the way offer a state-of-the-art theoretical overview of the commitment-based approach to speech act theory.