American Philosophical Quarterly Volume 50, Number 2, April 2013 ©2013 by the Board of Trustees of the University of Illinois THE SUPPORTIVE REASONS NORM OF ASSERTION Rachel McKinnon 1. Introduction In this paper I present my proposal for the central norm governing the practice of as- sertion, which I call the Supportive Reasons Norm of Assertion (SRNA). I argue that by properly understanding the relationship be- tween the goal of assertion and its nature as a social practice, we can recognize that there are conventional and pragmatic features in- ternal to the practice. These internal features should be made explicit in our articulation of the norm, and not treated as inessential to it. This feature of my view sets it apart from other extant proposals of reasons- based norms such as Jennifer Lackey’s Reasonable-to-Believe Norm of Assertion (RTBNA) and Igor Douven’s Rational Cred- ibility Rule (RCR). 1 While I cannot present a full defense of the norm—considering how it handles various data such as Moore’s Paradox and “How do you know?” 2 —I offer a preliminary defense as a launching point for future arguments. I begin with a brief presentation of SRNA. I then turn in section 3 to present a case of a warranted false assertion. In section 4, I return to more clearly explicate a number of key concepts of SRNA not addressed in section 2. 2. The Supportive Reasons Norm of Assertion (SRNA) I propose the following norm as the central constitutive norm for the linguistic practice of assertion: SRNA: (i) One may assert that p only if the speaker has supportive reasons for p, and, (ii) The relevant conventional and pragmatic elements of the context of assertion are present. Borrowing some analogous terminology from David Kaplan, we can say that SRNA has an invariantist normative character but a contextualist normative content. 3 These approaches are familiar from existing litera- ture, but they tend not to go together. I unify them by making the invariant component a type of indexical; the normative character is a function from context to content. Simply put, the context of an assertion determines the precise character of the norm for that con- text. Conditions (i) and (ii) are individually necessary and jointly suficient conditions for warranted assertibility, and this does not shift with context. Hence, the structure of the norm—the character—is invariant. There must be supportive reasons for the proposition asserted (I will say more on what