Assertion, Moore, and Bayes Igor Douven Institute of Philosophy, University of Leuven igor.douven@hiw.kuleuven.be Abstract It is widely believed that the so-called knowledge account of assertion best ex- plains why sentences such as “It’s raining in Paris but I don’t believe it” and “It’s raining in Paris but I don’t know it” appear odd to us. I argue that the rival rational credibility account of assertion explains that fact just as well. I do so by providing a broadly Bayesian analysis of the said type of sentences which shows that such sentences cannot express rationally held beliefs. As an interesting aside, it will be seen that these sentences also harbor a lesson for Bayesian epistemology itself. According to the knowledge account of assertion, the practice of assertion is governed by the rule that One should assert only what one knows. (1) Its many proponents point to various types of linguistic data and contend that the knowledge account explains these data better than any rival account of assertion. 1 Among these data are people’s general reluctance to assert, previous to the drawing of a lottery, that a ticket of that lottery is a loser; the fact that the question “How do you know?” is a socially accepted response to an assertion; and the fact that assertions of instances of the “Moorean” schemas ϕ, but I don’t believe ϕ (2) and ϕ, but I don’t know ϕ (3) sound, or would sound, positively odd to anyone’s ears. 2 That the knowledge account is able to explain all these data in a satisfactory way is beyond dispute. That it explains them best is not. Elsewhere I have defended what I called the rational credibility account of asser- tion, according to which assertions are governed by the rule that One should assert only what is rationally credible to one, (4) and argued that, on balance, this account provides a better explanation of the relevant types of phenomena than the knowledge account. 3 I say “on balance,” because I was 1 See, most notably, Williamson [2000], Adler [2002], and DeRose [2002]. 2 Famously, Moore [1962] contains the first discussion in the literature of instances of (2) and (3). 3 See Douven [2006]. 1