Synthese https://doi.org/10.1007/s11229-018-1682-2 A case for a certainty norm of assertion Esben Nedenskov Petersen 1 Received: 5 May 2017 / Accepted: 4 January 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract According to the widely endorsed Knowledge Account of Assertion, the epistemic requirements on assertion are captured by the Knowledge Norm of Asser- tion, which requires speakers only to assert what they know. This paper proposes that in addition to the Knowledge Norm there is also an Epistemic Propositional Cer- tainty Norm of Assertion, which enjoins speakers only to assert p if they believe that p on the basis of evidence which makes p an epistemic propositional cer- tainty. The paper explains how this propositional certainty norm accounts for a range of data related to the practice of assertion and defends the norm against general objections to certainty norms of assertion put forward by Duncan Pritchard, John Turri, and Timothy Williamson, by drawing on linguistic theories about epistemic modals and gradable predicate semantics. Together these considerations show that the prospects of a certainty account of assertion are much more promising than is usually assumed. Keywords Knowledge · Certainty · Norms of assertion · Moorean paradoxes 1 Introduction When a speaker asserts a proposition there are requirements which must be met for her assertion to be appropriate. According to the widely endorsed Knowledge Account of Assertion, KA, these requirements include the Knowledge Norm of Assertion, KN, which enjoins speakers only to assert propositions they know (DeRose 2002; B Esben Nedenskov Petersen esben@sdu.dk 1 Department for the Study of Culture, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark 123