Assertion, Knowledge, and Rational Credibility

Abstract

The view that assertions are governed by the rule that we should assert only what we know, is enjoying growing popularity. This paper argues that it is more plausible to assume that assertions are governed by the rule that we should assert only what is rationally credible to us. Specifically, it is shown that while the two rules are equally able to accommodate the relevant linguistic data, the latter is simpler than the former. There is a growing consensus among philosophers that the following rule governs the practice of assertion: One should assert only what one knows. (1) Call this the knowledge rule of assertion (or simply the knowledge rule), and call the thesis that (1) governs the practice of assertion the knowledge account of assertion. The present paper aims to make a case for a rival account of assertion, to wit (what I will refer to as) the rational credibility account of assertion. According to this, assertion is governed by the rational credibility rule, that is, the rule that One should assert only what is rationally credible to one. (2) Thus, on the view I will defend it is not required that a proposition be known for it to be warrantedly assertable; rational credibility suffices for that. In order to explain the methodology to be assumed in the following, I should note that in my view the project of determining which rule governs the practice of assertion is best not conceived as being an a priori investigation into the nature of assertion but rather as an empirical project, and that therefore any proposal that is being made in the course of this project is subject to the exact same standards of evaluation as are employed in the empirical sciences generally. That is to say, any hypothesis stating that a particular rule governs the practice of assertion must face the linguistic data about that practice; and if two or more such hypotheses are equally able to accommodate those data, then we may appeal to the so-called theoretical virtues (such as, most notably, simplicity) to help us choose between these hypotheses. I do not expect there to be any serious disagreement about the appropriateness of these methodological standards. Most proponents of the knowledge account 1See, for example, DeRose 1991, 1996, 2002, Brandom 1994, Williamson 1996, 2000, Sundholm 1999, 2004, and Adler 2002. In a rudimentary form, the view is already present in Black 1952, Moore 1962a, and Unger 1975.