In this paper, John MacFarlane proposes the following account of assertion (though he later amends it to accommodate relativity to a context of assessment as well as a context of utterance, but the amendments don’t touch on what I’ll comment on, so I’ll give the simpler characterization),
(Assertion-2) To assert a sentence S (at a context U) is (inter alia) to commit oneself to providing adequate grounds for the truth of S (relative to U), in response to any appropriate challenge, or (when appropriate) to defer this responsibility to another asserter on whose testimony one is relying. One can escape this commitment only by withdrawing the assertion.
MacFarlane then says something I think is quite astonishing:
Note that as far as (Assertion-2) goes, a liar is breaking none of the norms of assertion, provided she abides by the conditional task-responsibility to vindicate her claim when it is appropriately challenged, and withdraws her assertion when it is shown to be false. Here the present account diverges from the “knowledge account of assertion,” which takes both lies and unintentional falsehoods to violate the constitutive norm of assertion, “assert only what you know.” I think this is a point in its favor. Lying is not like cheating in baseball; it is more like stealing a base, which is a legal move in the game, but one that can be hard to get away with. Telling an unintentional falsehood is also not like cheating; it is more like an error in baseball.
This passage distinguishes MacFarlane’s view from Williamson’s view on the norm of assertion. In doing so, MacFarlane says that lying is like stealing a base in baseball, as opposed to, say, moving the fences farther back when the other team is at bat. It is this analogy that I find astonishing, since I can’t imagine crying “foul” over a stolen base but I certainly do cry “foul” when lied to. Unintentional falsehoods are one thing (I don’t think such assertions violate an appropriate norm of assertion), but there is critical difference between unintentional falsehoods and lies, a difference that MacFarlane’s account masks. Unintentional falsehoods are like errors in baseball, but lies are simply not like stolen bases in the relevant way.
This seems so obvious and MacFarlane is a really good philosopher, so one might suspect there is an easy reply to the objection. Here’s one such try: one might try to save Assertion-2 by attempting to explain my crying “foul” when lied to as traceable to norms of a different sort–moral norms, for example, rather than norms of assertion. But that move is too easy, I think: it would, by itself, bar any norm from being a norm of assertion, since one could always find some label other than ‘norm of assertion’ to undergird one’s complaints in the face of objectionable assertions (including cases where the conditional requirement posited by Assertion-2 is not met).
What MacFarlane’s examples show, I think, is that neither view is quite right, but Williamson’s view is much closer to the truth. The truth, I claim, is that epistemically justified belief is the norm of assertion. This view implies that in asserting p, one represents oneself as, or one commits oneself to, knowing that p is true, though it takes a bit of work to show that this implication holds. What’s good about this account is that it properly sorts unintentional falsehoods as akin to errors in baseball, which violate no rules, from lies, which are like moving the fences every half-inning, which is a violation of the rules.