Speaker: Alex Silk (University of Michigan / MIT)
Title: Information-Sensitivity in Deontic ‘Ought’ and ‘Must’
Date/Time: Tuesday Mar 20, 10:00AM-11:30AM
(Note unusual time and location)
There is a growing literature on how deontic modals can be interpreted with respect to bodies of information or evidence. However, previous treatments of information-sensitivity in deontic modals focus exclusively on ‘ought’ and ignore important differences between weak necessity modals like ‘ought’ and strong necessity modals like ‘must’. In this paper I attempt to delineate and capture such differences in information-sensitivity between ‘ought’ and ‘must’. Drawing on and revising a suggestion by Aynat Rubinstein, I argue that ‘ought’ and ‘must’ exhibit different conventional signals vis-à-vis common ground assumptions: ‘ought’, unlike ‘must’, conventionally signals that the truth and acceptance of the necessity claim—currently and throughout the evolution of the conversation—relies on certain assumptions not currently established in the global discourse context. This hypothesis helps generate correct predictions concerning the contrasting felicity conditions of ‘ought’- and ‘must’- sentences and meanings of ‘ought’- and ‘must’- conditionals. It also correctly predicts that certain types of modus ponens violations can occur because of the presence of ‘ought’ but not because of the presence of ‘must’.