Saturday, October 23, 2010

Expressivism and Evidence

Reading Blackburn's response to Parfit, I must confess that I found the parodic objections to 'Bramsey' more convincing than Blackburn presumably intended. 'Bramsey' holds that single-case probability judgments are really just expressions of one's credences or betting dispositions. As in Blackburn's moral expressivism, I take it that our normative commitments are, on this view, not objectively assessable (e.g. from an outside perspective). There's nothing in the world to make one person's expressed commitments more reasonable than another's. At most, I can offer a conflicting expression from my own (arbitrary) perspective.

Now, one Parfit-style objection to expressivism about single-case probabilities is as follows:
Bramsey suggests that betting dispositions might be mistaken in the sense that we would not have these dispositions if our standpoint were improved in certain ways. But to explain the sense in which this standpoint would be improved, Bramsey would have to claim that, if we had this standpoint, our betting dispositions would be less likely to be mistaken. This explanation would fail because it would have to use the word ‘mistaken’ in the sense that Bramsey is trying to explain.

Blackburn responds, "Comment should be unnecessary: Bramsey already explained why Bill is a better bookmaker than Kevin" -- namely, "Bill has, in thought or talk, a discursive practice of improving and refining his sensitivity to evidence, and thence his dispositions to buy and sell bets, and to make the judgments that are the propositional reflection of those dispositions. Kevin, of course, does the same, but is not nearly as good at it as Bill."

This strikes me as unsatisfying. For simplicity of exposition, let's focus in on a particular piece of evidence E: the fact that the horse Eclipse has a broken leg. And consider hypothesis H: that Eclipse will win the race. Now the question is: can the expressivist explain why it would be to the advantage of a book-keeper (selling bets on H) to learn E?

Here's a realist explanation: there's a metaphysical probability distribution over the possible worlds, corresponding to the antecedent objective chance of each world's being actualized. Now, the balance of probabilities more favours H in worlds where E is false than in worlds where E is true. So upon learning E, a book-keeper who takes this to lessen the chance of H is responding in a way that matches the real propensities of possible outcomes. Simply put: H is objectively less likely given E, and so it's no surprise that it's in the interests of a bookie to learn E, if he is disposed to respond by reducing his credence in H.

Now, the problem for the expressivist is that their view implies that there's no objective sense in which it's "more correct" to respond to E by lowering rather than raising one's credence in H. Of course, our epistemic practices favour this response. But we can imagine someone with wacky priors who instead takes the conditional probability of H given E to be greater than H given not-E. And it's an implication of expressivism that it's in some sense arbitrary which priors, or epistemic standards, we adopt. (Of course, from within their own practice, even expressivists will insist on first order claims about the other guy being "mistaken", and so on, but you know what I mean: it's arbitrary from an outside, objective perspective. The other guy can say all the same things about us, and there's nothing in the world that makes one of us right and the other wrong.)

So consider two bookies. Bill responds to E by lowering his credence in H. Bob responds to E by raising his credence in H. Objectively speaking, it's completely arbitrary which epistemic practice one happens to adopt. So in what sense is it to the advantage of both to learn E? Each might expect the new evidence to have positive utility for himself, insofar as their credence in H conditional on E differs from their credence in H. But each will likewise expect that the new evidence has negative utility for the other bookie, insofar as he's disposed to adjust his credence in H, upon learning E, in the opposite direction from them. Objectively speaking, it looks like a wash. Learning new "evidence" may cause changes in people's credences, which may either conform to our violate our epistemic norms; but if expressivism is true there's no further sense in which the changes could qualify as "improvements". (At least, assuming both agents are at least internally consistent, and so not susceptible to Dutch Books or the like.)

Am I missing something?

3 comments:

  1. I suspect Blackburn would reply that your explanation in terms of an objective metaphysical probability distribution is equally unsatisfying.

    He advances the following charge against Parfit:
    "In fact, Parfit’s own explanations of ‘what it would be’ for moral judgments to be true or false consists throughout in restating them in other terms. ‘What it would be’ for something to be wrong, for instance, is that ‘there are decisive reasons against doing it’ or similar things. But these are moral claims, voiced from within a particular sensibility. Parfit is to be applauded for denying that naturalism gives us, as it were, a non-moral vocabulary in which to moralize. But then neither does semantics, or meta-ethics. It takes a moral vocabulary to do it. And we expressivists wield that perfectly well: we speak English, after all."

    As applied to your example, I suspect he'd say that your explanation of what it is for one probability judgment to be correct amounts to just restating the claim that it is correct in other terms. You say that probability judgments are correct just in case they're objectively metaphysically correct. But on Blackburn's lights, until we have some more grip on what it is to think that a probability distribution is objectively metaphysically correct, (and he thinks the only grip to be had is an expressivist one) this won't tell us very much.

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  2. There might be worries about the realist story (here I really don't know enough about modalities). You might think that of all the possible worlds only one world has the probability of 1 to be 'to be actualised' and it is this one that I'm now pointing at, and all other worlds have a zero chance of being actualised. Also, it's not clear that, of all the worlds, there are fewer broken leg worlds in which Eclipse wins than ones that in which it doesn't. There are infinitely many of these worlds and many weird things happen in them.

    The arbitrariness challenge is interesting. If I remember this right, in his old paper 'Morals and Modals' Blackburn rejects expressivism of all modal talk just for this kind of reason but believes that in morals this isn't so problematic. Here we can go on living with our pro and con attitudes even if we might have had other ones. The practice we are in can continue despite this and play a role in action co-ordination whereas the modal practice would lose its point if it were arbitrary in the same way. Now, you might think that this is a strange difference between the practices.

    Also, note that no normative consequences follow from the claim that we could have had other attitudes. Not all of these would have been equally good. We believe that we by and large managed to get the ones we ought to have, and that things could have gone much worse. Of course, these claims too will be understood as expressing our current attitudes.

    The talk about further sense in which change qualify as improvements too is similar emoting (Ramsey's ladder is horizontal and all that).

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  3. Daniel - sure, it's open to Blackburn to argue that the realist is in the same (sinking) boat. But he was wanting to claim that the expressivist had a perfectly adequate explanation of why it would be to an agent's advantage to learn new evidence. I'm arguing that he does not have any such explanation. (Maybe others don't either -- though personally, I find the realist's explanation much more satisfying.)

    Jussi - If we want to claim that some events are objectively "weird" (and not merely contrary to our arbitrary psychological expectations), we seem committed to holding that there's a privileged probability distribution which assigns a lesser chance to those "weird" worlds than to more normative worlds. And if some non-actual worlds are weirder than others, they'd better not all have the same probability value (0) in this distribution.

    I'll have to dig up 'Morals and Modals'. If Blackburn rejects expressivism about epistemic norms, that'd seem to undermine his whole 'Bramsey' analogy.

    I think your third paragraph misses the force of my objection. I agree that Bramsey can continue to emote about how lucky he is that he has the "right" priors. But insofar as this is just another expression of his own attitutes, it is not a fact of the sort that could explain why it is to his advantage to acquire new evidence upon which to conditionalize.

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