Back from Australia

5 07 2007

I’m back from spending three weeks in Australia again – as usual, it was a very productive trip. It was also nice to get to attend the workshops on Norms and Analysis and Probability that went on last week. There were a lot of interesting talks there, so I won’t go through very many of them. Overall, I think the most interesting was Peter Railton’s talk in the first workshop, where he seemed to be supporting a framework for metaethics and reasons that is broadly compatible with the framework of decision theory. However, he brought in lots of empirical work in psychology to show that for both degree of belief and degree of desire, there seem to be two distinct systems at work – one more immediately regulating behavior, while the other being more responsive to feedback and generally regulating the first. It reminded me somewhat of what Daniel Kahneman was talking about in a lecture here at Berkeley a few months ago. But not being an expert in any of this stuff, I can’t say too much more than that.

Another particularly thought-provoking talk was Roy Sorensen’s in the Norms and Analysis workshop. He presented a situation in which you are the detective in a library. You just saw Tom steal a book, so you know that he’s guilty. However, before you punish him, the defense presents an envelope that may either contain nothing, or may contain exculpatory evidence (something like, “Tom has an identical twin brother in town”, or “The librarians have done a count and it seems that no books are missing”, which would make you give up your belief that Tom was guilty). Given that you know Tom is guilty, should you open the envelope or not? On the one hand, it seems you should, because you should make maximally informed decisions. On the other hand, it seems you shouldn’t, because either the envelope contains nothing, or it contains information you know is misleading, and in either case it’s no good.

Sorensen was arguing that you shouldn’t open the envelope, but I don’t think he succeeded in convincing any of the audience. But I think the puzzle sheds interesting light on what it takes to know that evidence is misleading, and how apparent evidence or the lack thereof really plays out when you know other background facts about where the evidence is coming from.

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5 responses

6 07 2007
Aidan McGlynn

There’s a related puzzle, attributed to Kripke, that Hawthorne discusses in K&L. It seems that if you know that p, and knowledge is closed under known logical implication, then you can know that all future evidence against p will be misleading. The puzzle’s set out in these terms on p73, and briefly taken up again in section 4.5, if you’re interested.

6 07 2007
Kenny

Thanks for the specific reference! He mentioned something called Kripke’s “dogmatic paradox”, but it’s good to know exactly where to find it.

14 07 2007
Mike

Kenny,

I wonder whether one of the worries concerns the possiblity of backtracking. Suppose I know that p and let p = I will not open the envelope. Of course, since I know it, it’s true that I will not open the envelope. But if I were to open the envelope, and read the evidence, it would be the case that ~p. And so were I to open the envelope it would be the case that I did not know that p. In that case, opening the envelope would not yield misleading evidence, but it is nonetheless true (I think) that I have no reason to open the envelope. So even if there is no misleading evidence in the envelope I might have no reason to open it.

20 07 2007
Sridhar

Sorensen’s situation is really interesting, but, I wonder, what is the reason for the additional complication of the possibility that the envelope may contain nothing? Is this really relevant to the core conflict?

20 07 2007
Kenny

I think the reason for that extra twist is that it’s the only way you can guarantee that you’ll always get the envelope, so that the presence of the envelope doesn’t itself count as evidence.

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