Evidence for presuppositions

One of the things evidential challenges do is to question what grounds we have for our antecedent beliefs. Indeed, that's one of the main things they do. Maybe it's common knowledge that we all believe that p, but we haven't thought much about why we all believe that p. This is just the sort of case where it might make sense to stop and wonder whether p—which is mutually recognized to be something we believe—is actually supported by our evidence.

I think that this observation undermines a claim Michael Blome-Tillmann makes in his book Knowledge & Presuppositions. The key idea there, as in his earlier paper of the same title, is to embrace a Lewisian from of contextualism about 'knows', but where Lewis's 'Rule of Actuality' is replaced by a 'Rule of Presupposition'—that which is consistent with the presuppositions in a conversation is not properly ignored. Ad Michael characterizes conversational presuppositions in terms of dispositions reflective of mutual belief.

Michael considers (p. 99) this dialogue:

A: I know that animal is a zebra.
B: How do you know that it isn't a mule cleverly painted to look like a zebra?
A: Hmm, for all I know it is a painted mule. So I was wrong. I didn't know that it is a zebra after all.

In a strategy unlike the canonical one (supposing that final A's self-attribution of error is mistaken), Michael thinks that A's final response is wholly correct, and that the initial utterance is false. He thinks that the painted mule hypothesis is relevant, even at the start of the conversation. Here's why:

[B] does not pragmatically presuppose that the animals are not cleverly painted mules—neither before nor after asking her first question. Since B asks whether A can rule out that the animal is a cleverly painted mule, B is clearly not disposed to behave, in her use of language, as if she believed it to be common ground that the animal is not a cleverly painted mule. For if she were so disposed, she would certainly not have asked that very question. (100)

This seems to me simply to be wrong, for the reason laid out in my opening paragraph. Asking whether p is ruled out by evidence seems to me wholly consistent with thinking it to be common ground that p.

(Although I think it's independent, this point points to the same conclusion, and has an argumentative similarity with, the one I press against Michael's view in this paper.)

Ignorance and Presuppositions

I have completed a draft of a new short discussion piece on Michael Blome-Tillmann's (2009) Mind paper, "Knowledge and Presuppositions". It is essentially a development of this blog post from a year and a half ago. (I'd forgotten about it, to be honest -- I rediscovered it as I finished drafting.)

My new paper: Ignorance and Presuppositions

I hope to submit it soon; any comments would be very welcome.

Presupposition and 'Knows' Contextualism

In a recent paper in Mind, Michael Blome-Tillmann defends a form of 'knows' contextualism that is broadly Lewisean. His project is, in its broad forms, very similar to that in one of my forthcoming papers. In my paper, I argue that Lewis's particular suggested rules for proper ignoring are inessential to the central contextualist insight, which is that one can model 'knows' in a way similar to context-sensitive quantifier domains, and that maybe he should have just rested happily with the latter, rather than trying to articulate all the relevant rules. Blome-Tillmann agrees with me that Lewis's particular rules are inessential to his broader project, but, unlike me, he goes on to attempt the ambitious task of articulating rules that will do the relevant work. So rather than rest content with the main contextualist point, as I do, Blome-Tillmann argues for a different solution than Lewis's to Lewis's original, more ambitious project. The suggestion is to replace the Lewisean 'Rule of Attention' with a 'Rule of Presupposition':

(RP) If w is compatible with the speakers' pragmatic presuppositions in C, then w cannot be properly ignored in C.

Pragmatic presuppositions here are meant to be understood in the Stalnakerian way. The basic idea is that there are different ways to attend to skeptical possibilities; if you just listen to a presentation of them but continue to presuppose them not to obtain, then you can still 'properly ignore' them. But if our common ground shifts so as to include those possibilities, then they are no longer properly ignored.

It may well be that the Rule of Presupposition does a better job with cases than does the original Rule of Attention on the whole. But it does worse in at least some cases. Consider some expression PHI, used to pick out an individual, whose felicity requires that some p be presupposed. For example, the expression "the man sitting at the table" requires it to be common ground that there is a uniquely salient man sitting at a uniquely salient table. Now consider a sentence of the form "PHI does not know q", where p obviously entails q--e.g., "the man sitting at the table does not know that there is a table."

Intuitively (once we've bought into contextualism), some such sentences can both be felicitous and vary in truth from context to context, even when discussing the same subject and proposition. For example, someone in a skeptical context might say "the man sitting at the table does not know that there is a table" truly, even as, in another, nonskeptical context, someone might say "the man sitting at the table does know that there is a table" and speak truly. This is the sort of result contextualists want to capture. But I don't think Blome-Tillmann can capture it. Anybody who utters that sentence felicitously is in a context in which it is presupposed that there is a table. (The previous paragraph gave a recipe for coming up with lots of similar examples.) Blome-Tillman's Rule of Presupposition, then, cannot explain the difference between the skeptical context and the nonskeptical one with respect to whether non-table-including possibilities are properly ignored. And none of Lewis's other rules, besides the Attention one that Blome-Tillman rejects, looks well-suited to do the job either.

So I don't think that presupposition can do the work Blome-Tillman wants it to do in articulating what possibilities are properly ignored. I still think it's best not to get too worked up about these details, and rest content with the contextualist insight.