Knowledge and epistemic necessity John Hawthorne Published online: 6 June 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Claims of the form ‘I know P and it might be that not-P’ tend to sound odd. One natural explanation of this oddity is that the conjuncts are semantically incompatible: in its core epistemic use, ‘Might P’ is true in a speaker’s mouth only if the speaker does not know that not-P. In this paper I defend this view against an alternative proposal that has been advocated by Trent Dougherty and Patrick Ry- siew and elaborated upon in Jeremy Fantl and Matthew McGrath’s recent Knowl- edge in an Uncertain World. Keywords Knowledge Á Epistemic modality Á Epistemology 1 Introduction Claims of the form ‘I know P and it might be that not-P’ tend to sound odd. One natural explanation of this oddity is that the conjuncts are semantically incompat- ible: in its core epistemic use, ‘Might P’ is true in a speaker’s mouth only if the speaker does not know that not-P. This semantical property can also form the basis for an explanation of why claims of the form ‘P but it might be that not-P’ sound odd, at least assuming that knowledge functions as a norm for assertion. In this case, the conditions for the truth of (and hence felicitous assertion of) the right conjunct are incompatible with the conditions for felicitiously asserting the left. This approach to ‘might’ claims—call it the standard approach—is one that many, including myself, are very sympathetic too. Recently, Trent Dougherty and Patrick Rysiew have advocated a competing idea, one that has been endorsed and elaborated upon in Jeremy Fantl and Matthew McGrath’s recent Knowledge in an Uncertain World (Fantl and McGrath 2009). J. Hawthorne (&) Magdalen College, University of Oxford, Oxford OX14AU, UK e-mail: john.hawthorne@philosophy.ox.ac.uk 123 Philos Stud (2012) 158:493–501 DOI 10.1007/s11098-012-9960-1