Suppose that you're offered the following bet: If a coin lands heads you will win $1.50. If it lands tails you will lose $1. Your credence in heads is .5. (Assume that the fact that you're being offered this bets gives you no information about the odds of heads or tails.) Is it rational to accept the bet?
According to expected utility theory, it is, and this seems right (setting aside risk aversion). What does a knowledge-action account advise? Well, that depends. Consider two possibilities:
1) You are certain that the coin is fair, so you know that the objective chance of heads is .5. You can use the fact about the objective chance as a reason to take the bet.
2) You have no idea whatsoever about the bias of the coin. Using the principle of indifference, you assign credence .5 to heads. What knowledge do you have that could makes it rational to accept the bet? (Hawthorne and Stanley don't want to allow knowledge of subjective credences.) If there isn't any relevant knowledge, then it's not rational to accept the bet.
Here the knowledge-action account seems to makes a distinction between the two cases that expected utility theory does not. This is worrisome for the knowledge-action account.
Note: Expected utility theory will distinguish between the two cases when you're allowed to acquire additional evidence first. But that's not an option here.
I just got back from Boston, where I spent most of spring break. In Cambridge, there is a great bookshop (the Harvard Book Store) where they have an Espresso Book Machine. I’d read about these things before, but this was my first chance to see one in action – and I was pretty impressed.
Here's how it works. In the shop, they have a computer on which there is a searchable database of (type) books. You choose one, and the Espresso Book Machine prints out a token for you on the spot. I asked for a copy of Royce’s The Religious Aspect of Philosophy. They downloaded a scan of the book from Google, printed it out, and then charged me $8 for the book. This is a bargain – it costs $40 from Amazon. The whole process took about ten minutes; the book was still warm as I walked out of the shop. It’s a paperback, and it looks and feels cheap, but it’s hard to complain given the price.
It seems to me that this is an exciting thing for people who do history of philosophy. Many old books – which are out of print and hard to get hold of – are actually in the public domain. From now on, it should be possible to get cheap copies of these books using an Espresso machine.
According to Wikipedia, each one of these machines costs at least $75,000 – so a bookshop will have to get a hell of a lot of use out of one before it even makes enough to pay off the initial investment. And as I say, the books that the machine makes are of rather a low quality. However, if the technology improves, or gets cheaper, it may make a big difference to the way we buy books. Perhaps bookshops in the future will have just a few tables of books at the front (for browsing), plus the inevitable coffee-shop, and then a big printer in the back rather than rows of shelves.