Jerry Dworkin pointed out to me that Mike Leigh’s film “All or Nothing” contains a scene that seems to support interest-relative-invariantism. The script is here, though be warned that link contains pop-ups.
Husband: Give us a clue, then.
Wife: ‘Biblical son of Isaac, five letters.’ Starting with a ‘J.’
W: Oh, yeah.
H: No, it ain’t. It’s what’s-his-name. Jacob.
W: Are you sure?
W: It’s a thousand pound prize.
H: Is it? No, I ain’t sure, then.
Well, maybe it is only interest-relative-invariantism about ‘sure’, rather than ‘knows’, but it seemed like a good way to celebrate the publishing of Jason Stanley’s book on IRI. More on IRI after the fold.
My version of IRI was based on the following two idea. S has a justified belief in p if her degree of belief in p is justified, and that degree is high enough to amount to a belief. Since what degree of belief S must have in p to count as believing that p is sensitive to S’s context (or interests or whatever) this is something like a form of IRI about justified belief.
Now it would be nice if that ‘if’ in the theory could be strengthened to an ‘iff’, but I don’t think that’s so, because of the following two cases.
Confident Carla and Sceptical Suzy each have the same evidence e, and each are in the same practical situation with respect to p. In that situation, degree of belief 0.8 suffices for belief in p. That is, they don’t face any choices that amount to bets on p at odds greater than 4 to 1 against.
- The evidence e justifies a degree of belief in p of 0.9.
- Confident Carla is too confident about the strength of the evidence; her degree of belief in p is 0.95.
- Sceptical Suzy is too sceptical about the strength of the evidence; her degree of belief in p is 0.85.
Question: Which of the two of them justifiably believe that p? I’m inclined to say that they both do, though I’m more confident about Suzy than about Carla. But the little theory above, if strengthened to a biconditional, would say that neither justifiably believe that p. That seems to be a problem.
I think the thing to say is that S justifiably believes that p iff S believes that p, and S is justified in having a high enough degree of belief in p to count, in her context, as believing that p. That makes both Suzy and Carla justified believers, though it is a more complicated theory than the one I hoped would be true.