Saturday, September 5, 2009

Evidence, knowledge, seemings, and all that

Scarlet: Does the prosecution have solid evidence against Mustard?
Green: Here's the evidence they have against him: namely, that he was the last one to see the victim alive, that he lied about his whereabouts on the night of the crime, that his fingerprints were on the murder weapon, and that he wrote a letter containing details the police think only the killer could have known. Of course, I don't know if he's the last one who saw the victim alive, I don't know if he lied, I don't know if his fingerprints were on the murder weapon, and I don't know if he wrote a letter containing any details about the crime.

It seems to me that Green's remarks are contradictory in either the way that contradictions are or the way that Moore Paradoxical assertions are. If E requires K, I take it that Green is saying that the prosecution knows p, q, and r but that he does not know p, q, and r. If E requires T, I take it that Green is, in effect, asserting that p, q, and r are true but that he does not know this. If, however, A needn't know p or be right about p for p to be part of A's evidence, I can't see why it seems contradictory in the way that contradictions or Moorean absurd assertions are for B to say A's evidence includes p but she (i.e., B) doesn't know that p. Since K entails T, I think this is a decent argument for the claim that whatever else a proposition must be to included in someone's evidence, the proposition must be true.

Contrast the above with this:
Scarlet: Why does the prosecution believe Mustard did it?
Green: It seemed to them that he was the last one to see the victim alive, that he lied about his whereabouts on the night of the crime, that his fingerprints were on the murder weapon, and that he wrote a letter containing details the police think only the killer could have known. Of course, I don't know if he's the last one who saw the victim alive, I don't know if he lied, I don't know if his fingerprints were on the murder weapon, and I don't know if he wrote a letter containing any details about the crime.

That doesn't seem odd in the least. Moral of the story?

If it seems to S that p, it doesn't follow that p is part of S's evidence. It may be that S's evidence includes a related proposition; namely, the proposition that it seems to S as if p, or it seems that p, or something like that. But, _that_ proposition about seemings, appearances, etc... will be part of S's evidence only if it is true (if the above is right). Moreover, I think there's some reason to think that our evidence will not be limited to such seemings or appearances of a kind that would save mentalism.

Why? Take all the true seemingsy and appearancy propositions that would be true if instead of perceiving what you perceive you were a BIV. This will be a proper subset of the propositions that are part of the content of experience since, after all, your experiences would not be wholly veridical if you were a BIV. Is there any good reason to limit your evidence to those propositions that would be true only if you were a BIV? Only if there's a good reason to think that the propositional content of experience can justify belief only if they are the sort of propositions you can know to be true via introspection. I doubt there's any such reason.

4 comments:

John Turri said...

Clayton,

This doesn't sound contradictory to me:

S: What's the prosecution's evidence?
G: Now mind you, I can't vouch for this -- I don't know whether it's good or bad evidence -- but here it is: P, Q, and R.

I think part of the oddness you detect comes from the fact that describing something simply as "evidence" implicates that it is good evidence. Something very similar happens with describing someone's "reasons."

Brandon said...

I'm inclined to agree with John here; what makes Green contradict himself in the first scenario is that he is supposed to be listing "solid evidence" -- i.e., things that, if the case, would be genuine evidence, and are known to be the case. So it's surprising that he lists something as solid evidence and then denies that he knows that its solid, i.e., locked in so as to be known to be right.

Clayton said...

Hey John and Brandon,

You don't think that this sounds contradictory:

S: What's the prosecution's evidence?
G: Now mind you, I can't vouch for this -- I don't know whether it's good or bad evidence -- but here it is: that Plum saw him at the scene of the crime, that his fingerprints were on the weapon, and that a jail house snitch said that he did it.

Suppose the conversation continues just a bit further:

S: Wait, so was Mustard seen at the scene of the crime?
G: Look, part of the evidence that they have against him was that he was seen at the scene of the crime. It just happens to be that he wasn't.

Yeah, that last part doesn't make any sense to me. We can talk about a body of evidence being bad evidence for guilt because it isn't likely given the evidence that the guy is guilty. But, it still seems odd to me to say (even at the tail end of an exchange where it is clear that the speaker doesn't think that the evidence is "good") that p is part of S's evidence but ~p.

John Turri said...

Clayton,

I think there's a potentially important ambiguity in the way you put things.

You say, "their evidence is that P, that Q, and that R." But this might be taken to mean "their evidence is the fact that P, the fact that Q, and the fact that R." Or it might mean, "the claim that P, [etc.]," where 'claim' just means 'proposition'.

When it's understood factively, it sounds contradictory. But when it's understood propositionally, it doesn't.

S: What's the prosecution's evidence?
G: The claim that P, the claim that Q, and the claim that R.
S: Oh, so it's true that P?
G: No, and I never said it was true. I said it was their evidence.
S: I see.

That seems perfectly fine to me. G's statements don't seem contradictory, or even odd to me.

I also think this sounds perfectly fine:

"Their evidence for denying evolution was the claim that everything the Bible says is true. But of course they're wrong about that -- not everything the Bible says is true."