I wonder if anyone has insight into why Quine never ran any of his epistemology off of degrees of belief (unless, of course, I’m just unaware of something in the Quinean corpus, which there is some chance of, since I know I haven’t looked at all of it). I don’t know the answer, but here’s a guess.
Suppose one thinks that there are both beliefs and degrees of belief, and that they are related by the following necessary equivalence:
S believes that p iff S’s confidence level regarding p exceeds some threshold T.
One can fill out the Lockean picture of the relationship between belief and degree of belief by accepting this equivalence and taking the direction of reduction to go from left to right. That is, the fundamental reality is degree of belief, with the derived reality that of belief.
How would one oppose this Lockean thesis? Well, obviously, one might think the equivalence claim is false, either by denying any relationship between beliefs and degrees of belief, or by doubting the existence of one of the two. Perhaps Richard Jeffrey is the most famous denier of belief, but it is hard to find an explanation by those who think there are no degrees of belief. I found one though: from P.M.S. Hacker, “Of the Ontology of Belief,” where he says,
But there are no degrees of belief, so belief cannot be a feeling. I cannot believe that p more than you do, although I may be more certain than you that p. I cannot believe that p just a little or very much, although I can be inclined a little or very much inclined to believe that p. Of course, one may strongly or firmly believe that p (though not “weakly” or “moderately”), but this does not indicate a degree of belief. It signifies the strength or firmness with which one cleaves to the belief one has. It is the ease or difficulty of shaking the belief in question, and not the belief itself, that has degrees. It makes sense to ask how convinced, doubtful, suspicious, confident, etc. someone is that p, but not to ask how belief-ful or how much one believes that p. It is the belief-related adjectives that do this work, not the noun “belief”. The evidence I have in favour of its being the case that p may increase, but my belief that p does not therefore increase, although my conviction, certainty or confidence that p will. (p. 5 of pdf file located here).
But what if one wishes not to abandon the equivalence? One might insist that no reduction in either direction is possible, but one might also try to reduce degrees of belief to belief itself. My suspicion is that Quine may have thought this (though, as you’ll see, I have very little evidence). Here’s why I suspect this. The only person to my knowledge that suggests a possible way of reducing left-to-right is Gil Harman. I don’t have the quote with me, but what I recall is that he says something like this: degree of belief is an epiphenomenon of how revision of belief occurs.
If we wax metaphorical a bit, we can put Harman’s idea into the language of the web of belief, where depth in the web signals greater resistance to revision in the face of recalcitrant experience (or other learning). We can use various measuring strategies (e.g., betting behaviors) to give a rough guide as to how to generate comparisons between various levels of resistance to revision. That’s how we get degrees of belief out of belief. Many of the things that Quine says about the web of belief are suggestive of such a view, so I wonder if Quine would have preferred the anti-Lockean explanation.
OK, there are questions to be answered here, but if we suppose that the story goes something like this, then we’d have an explanation of why Quine does epistemology through belief rather than degrees of belief. With other epistemologists, we might cite lack of familiarity with formal techniques and methods as the explanation, but I think it would be slightly bizarre to consider such an explanation for Quine!
Anyway, just an idea, and I’d love to hear other ideas as to why Quine doesn’t show any interest in degrees of belief.