## Sunday, November 16, 2008

### Justification and evidence

Consider:

JE: The belief that p is part of what justifies S in believing that q only if p is included in S’s evidence.

I think this principle is an assumption in C & K's attack on Williamson. Is it true? That is difficult to say. Here's an argument that it's not, inspired by Dodd's criticism of Williamson and some stuff Pryor has been dealing with because of his dogmatism. Suppose that p is the belief that I have hands and it is supported by experience. Let's say that the experience is the evidence for p. If you accept dogmatism, you'll say that the evidence of the senses could suffice for justified acceptance of p even though p is not certain given the evidence. But, then it seems that once p is itself part of the evidence, the evidential probability of p raises from some value less than 1 to 1. More plausible, I think, to say that if you accept that you can justifiably accept p on the basis of evidence that leaves p less than certain, that is precisely why justified acceptance of p does not necessitate p's inclusion in your evidence.

I haven't checked, but I think this deals with C & K's argument that E = K is incompatible with closure as well.

[Update]
I haven't addressed Juan's comments yet, but I have a very rough draft.

Juan said...

Hi Clayton,

A couple of quick related comments. First, "evidence" is said in many ways, of course. Maybe some uses of "evidence" are such that what you say (two posts ago) is true. We are interested in the sense of evidence in which evidence is whatever justifies you, and whatever justifies you is evidence. This is, pretty clearly, what Williamson is interested in too. The quote we have in our paper says the following:

"[I]n any possible situation in which one believes a proposition p, that belief is justiﬁed, if at all, by propositions q1 , . . . , qn (usually other than p) which one knows. (. . . ) Now assume further that what justiﬁes belief is evidence (. . . ). Then the supposition just made is equivalent to the principle that knowledge, and only knowledge, constitutes evidence."

So, if what justifies belief is evidence, and if (part of) what justifies the subject in believing the target proposition is a false proposition, then a false proposition is evidence. (This is too quick, of course. Mark Schroeder's "Having Reasons", available from his website, contains some relevant and fascinating discussion.)

Clayton said...

Hey Juan,

I enjoyed the paper that you wrote with Holly and I'm sympathetic to your ultimate conclusion, but I'm still not convinced that you are getting the right conclusion for the right reasons. Suppose that the passage you cite does support the attribution you are making to Williamson. He could just say that you are right but then revise his view to say that the kind of evidence he's interested in isn't the kind that you are and retain E = K.

That's not the greatest response, but this one is slightly more promising. Let's assume Williamson wants to hang onto everything in this passage. Here's how he could do it. He could deny JE. In Coins, Smith believes two things:

(d) Jones is the man who will get the job, and Jones has ten coins in his pocket.

(e) The man who will get the job has ten coins in his pocket.

He could say that in Coins Smith is justified in believing (d). He could say that he's justified in believing (e). It's true that the belief that (d) is false, so the proposition that d is true cannot be part of his evidence. However, the belief that (d) gets involved in the justification by transmitting the evidence for believing (d) [evidence which Gettier says consists of propositions known to be true] to the belief that (e) without adding any additional evidence. The justification for believing (d) just is the justification for believing (e). The justification for believing (d) does not involve the false proposition that (d) is true. So, the justification for believing (e) does not include the proposition that (d) is true. However, you are right that the false belief is 'involved' in some way in the justification of believing (e), not as a source, but as a 'director' if you like.

Anyway, I think there's just a much easier way of refuting E = K. The problem isn't that evidence must consist of true propositions. The problem is that it isn't true that, necessarily, if A knows p and B doesn't know p, A's evidence includes a proposition that isn't included in B's. Fake barn cases seem to show as much.