Only Knowledge is Evidence

Juan Comesaña and Holly Kantin have a paper forthcoming out in PPR that argues against Williamson’s E=K thesis. (UPDATE: Actually it’s not forthcoming, it’s in the March 2010 edition. My apologies.)

Now I don’t believe E=K. But I do sorta believe that only knowledge is evidence, and that’s the target of most of their arguments. They call the thesis that only knowledge is evidence E=K 1.

They argue that certain Gettier cases are impossible given E=K 1. Here’s one such Gettier case.

Coins. You are waiting to hear who among the candidates got a job. You hear the secretary say on the telephone that Jones got the job. You also see Jones empty his pockets and count his coins: he has ten. You are, then, justified in believing that Jones got the job and also that Jones has ten coins in his pocket. From these two beliefs of yours, you infer the conclusion that whoever got the job has ten coins in his pocket. Unbeknownst to you, the secretary was wrong and Jones did not get the job; in fact, you did. By chance, you happen to have ten coins in your pocket.

Now this seems like an easy case to me. “You” have two pieces of evidence. First, that Jones has ten coins in his pocket. Second, that the secretary said that Jones got the job. Those bits of evidence justify a belief that whoever got the job has ten coins in his pocket. But Comesaña and Kantin think this isn’t a good enough explanation of the story. They insist that the intermediate conclusion that Jones got the job is also part of the evidence. I’m not sure quite why they think that; it seems contradictory to me to say that p is part of someone’s evidence, but ¬p. They do offer this consideration.

And there is no argument that we can think of to the effect that your belief that Jones got the job plays no part whatsoever in justifying you in thinking that whoever got the job has ten coins in his pocket.

That seems like a failure of imagination to me. In general, there’s always an argument to the effect that p. Namely God knows that p, therefore p. Now the first premise might occasionally be false, but still, it’s an argument.

A little more seriously, here’s one such argument.

  1. Only knowledge justifies.
  2. “You” do not know that Jones got the job.
  3. So the (false!) proposition that Jones got the job plays no part whatsoever in justifying you in thinking that whoever got the job has ten coins in his pocket.

I know that Comesaña and Kantin don’t believe the first premise. Indeed, that’s the conclusion of their paper. But to use the falsity of that premise in an argument against it seems somewhat circular.

4 Replies to “Only Knowledge is Evidence”

  1. Brian,

    I can’t see the circularity worry, unless there’s a circularity worry whenever someone argues against a view by pointing out what they take to be an implausible consequence. One can always meet the demand for an argument for the supposedly implausible consequence by pointing out (with the objector!!) that it’s a consequence of one’s view. I don’t see how that can be enough for the objector to be guilty of begging the question, though, if the consequence does seem genuinely implausible (at least on the face of it), which this one does to me.

    I took it the quote about there being no argument, the authors were looking for independent grounds for thinking that the conclusion isn’t implausible after all, and failing to come up with any. You do give such grounds, to be sure, namely the claimed contradictoriness of ~p and p is E for someone. But your post suggests that you think there’s a separate issue about circularity, and that’s what I can’t see.

  2. Thanks for discussing this, Brian. One correction: E=K 1 is not the thesis that only knowledge is evidence. Rather, it is the following:

    E=K 1: The proposition that p justifies S in believing that q only if S knows that p.

    (That only knowledge is evidence follows from E=K 1 and the claim that only evidence justifies, which Williamson also accepts.)

  3. Aidan,

    Fair enough. I guess I just don’t get the relevant intuitions here. It seems natural to me to say that the underlying knowledge is what justifies, and its justificatory force is transmitted to the true conclusion. But if one thought it was intuitively obvious that the false intermediate premise also had a justificatory role, then it wouldn’t be circular to point out that intuition was incompatible with E=K.


    Oops, I was sloppy there wasn’t I? I also think that (at least in the case in question) only evidence justifies, but you’re right that’s a distinct claim from E=K, or from E=K 1.

  4. One worry I had about the argument against E=K has to do with the move from the claim that (i) some belief figures in the explanation as to how some other belief gets justified to the further claim that (ii) that belief figures in the explanation only if it provides additional evidence for accepting the conclusion. I don’t see why a defender of E=K can’t just say this: it’s possible that my justified belief that p figures in the justification for believing q because it provides the support for believing q that my total evidence provides for believing p.

    Presumably, p isn’t part of the total evidence that supports believing p. So I don’t see why we have to assume p is part of the evidence that supports q in order to see how justifiably believing p is part of what explains justifiably believing q.

    There’s something else that worries me about this style of attack on E=K. As Juan reminded me earlier, there’s lots in the paper that he and Kantin wrote that was granted to Williamson that we shouldn’t think they endorse (e.g., about the role evidence plays in justification), but if we take their objection to be an objection to E=K in particular (and not these ancillary assumptions), the objection is really an objection to any view on which only true propositions constitute evidence. Let’s call this “factivity”.

    You could argue that factivity is false on the grounds that evidence isn’t propositional, but this isn’t the route that they go. Instead, it seems the problem is the thought that the propositions have to be true to be evidence. In the cases in the paper, what would these propositions be?

    In Coins, I take it that the idea is that the following is true:
    (1) What’s your evidence that the man who got the job has ten coins in his pocket? It’s not just that the secretary said that Jones got the job, but also that Jones got the job and had ten coins in his pocket.

    In the discussion of closure, I think we’re supposed to accept the following:
    (2) What’s Terry’s evidence for believing that there’s a non-human animal in the neighborhood? Among other things, it’s that there’s a dog in the neighborhood.

    I think what bothers me about this line against E=K (and similar arguments in other recent papers attacking E=K) is that when we write about the evidence and reason ascriptions that identify false propositions as the subject’s evidence, those ascriptions are intuitively false and intuitively seem to entail false propositions. (1), for example, strikes me as false. So, I think I agree with Brian that it seems just contradictory to say both that ~p and that p is part of someone’s evidence. Am I wrong that (1) and (2) are supposed to come out as true if the objection to E=K is sound and we’re assuming that propositionality is true?

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