The single norm of assertion

Abstract

Timothy Williamson holds that the knowledge rule of assertion, according to which one should assert only what one knows, is the single norm of assertion. I explain and defend Williamson’s thesis. I identify three key features associated with the thesis: the single norm of assertion should be constitutive, individuating and basic. Roughly, a constitutive rule of a speech act governs every possible performance of the act. A rule of assertion is individuating if it differentiates assertion from every other speech act. Finally, a rule of assertion is basic if it does not derive from other rules governing assertion, or other speech acts. I thus construe Williamson’s thesis as the claim that the knowledge rule is the only individuating, constitutive and basic rule of assertion. This thesis is compatible with the idea that assertion is governed by non-epistemic constitutive rules such as moral and prudential rules. Since these rules are not individuating, there is no need to understand Williamson’s thesis as bearing solely on the epistemic rule of assertion. I explain how the existing arguments in favor of the knowledge rule can serve to support the thesis that this rule is also the single norm of assertion. I also respond to some objections against the knowledge rule, and criticize alternative rules.