Deontic Modality
Jussi Suikkanen · Analysis · 2018
The English language contains a number of expressions that often stand for concepts called the ‘deontic modals’.1 These expressions include ‘must’, ‘should’, ‘ought’, ‘may’, ‘can’ and the like. The deontic modal concepts, which these words are often used to express, are interesting in many ways. First, there are logical connections between them – for example, they can be ordered in terms of strength. That I must go home now entails that I ought to go home now, and that proposition furthermore entails that I may go home now. Yet, the inferences in the other direction from ‘may’ to ‘ought’ and from ‘ought’ to ‘must’ are not valid. The strength of the deontic modals thus varies from the strict necessity modals (‘must’) to weak necessity (‘ought’) and possibility modals (‘may’). Deontic modals also come in a number of different ‘flavours’. If I say that I must go home now, the intuitive idea is that I am using ‘must’ in a different sense depending on whether I express the thought that overall I have most reason to go or the thought that morality, prudence, law or some other normative standard requires me to do so. These same words can also be used to express different non-deontic modalities. For example, when I say that the train ought to be at the station, I am using ‘ought’ in an epistemic sense that is related to how things would normally be relative to what information I have.2