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December 1st, 2009

More Thoughts on Evidence

Thanks to the feedback I’ve gotten already on evidence. Here are three other questions that I’ve already got from looking at those suggestions, and thinking about related stuff.

1) In the literature on testimony, there are several writers who deny that testimony is a source of evidence. Rather, they say, testimony provides a kind of non-evidential warrant.

Now I’m rather sceptical that this is the right approach to testimony. But one thing that’s worth thinking about from a perspective of a theory of evidence is what it could mean for this to be true. On some theories of evidence (on E=K for instance) it’s hard to see how this could even be a coherent position. I suspect it is a coherent position, and that’s a reason to doubt E=K. But turning this into an argument requires saying more about what non-evidential warrant might be, and hopefully saying that will provide some clues as to what evidential warrant might be!

It might be helpful here to think about the kind of warrant we get from doing simple logical inferences. When we validly infer q from p, and thereby come to know q, presumably p is part of our evidence. But I don’t think it is true in general that the fact that p implies q is part of our evidence. If it is, then we should also say that the fact that p, and p implies q, together imply q is part of the evidence, and so on ad infinitum, and that strikes me as absurd. So in inference there are things that we know, and that provide warrant, but which are not part of our evidence, properly construed. So I am sympathetic to the idea of non-evidential warrant, though I’d like to know a lot more about how it is supposed to work.

2) It’s interesting to think about what evidence a person has. And it’s interesting to think about what evidence a person has for different claims H, where H is a claim that the person could be considering. Here’s a third question: Which of those two concepts is primary? I sometimes think E=K is best considered as a view where the concept of evidence for is primary, and evidence simpliciter is a derived notion.

What I mean by this is to say that E is part of S’s evidence just is to say that E is part of S’s evidence for some hypothesis, and the order of explanation/analysis here goes from right-to-left. One question is whether that’s the right way to take E=K. (I think it makes the best sense of some arguments for E=K.) The other question is whether it is the right way to think about the question more broadly. Should we analyse ‘evidence for’ by first offering a theory of evidence, and then asking what of that evidence is evidence for the hypothesis in question, or should we analyse evidence by first offering a theory of evidence for different hypotheses, and then asking what propositions are evidence for some propositions or other? This seems like a fairly deep question, and I don’t know how to attack it.

3) In law, evidence typically does not consist of propositions. In philosophy we’ve focussed our attention on propopsitional evidence. Or at least we have recently. When Quine said evidence was sensory irritations, he presumably was not saying that our evidence consists of facts about sensory irritations. We might have made a deep mistake here; maybe propositional evidence is just a special kind of evidence.

Posted by Brian Weatherson in Uncategorized


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4 Responses to “More Thoughts on Evidence”

  1. Kent Staley says:

    It’s interesting to me that there seems to be a divide between how epistemologists and philosophers of science think about evidence. There is a pretty rich literature on evidence in philosophy of science that (apart from the Bayesians who also do formal epistemology) seems pretty orthogonal to what epistemologists seem to be discussing.

    One thing worth noting about the phil-sci debates is that, although Bayesian views are certainly influential, there is a proliferation of alternatives. For example, I’m teaching four different theories in a seminar on evidence next semester, of which Bayesianism is just one; the other three are likelihoods-only (e.g., Sober), error-statistics (Mayo), and Achinstein’s probabilistic-explanatory hybrid. All of these are theories that attempt to articulate the conditions under which data E constitute evidence for a hypothesis H.

    But it is true that the epistemological content of some of these approaches is pretty underdeveloped, and that is unfortunate (I’m starting work to remedy this in the case of error-statistics, but it’s definitely under development).

    I think Achinstein’s account perhaps deserves more attention than it gets from epistemologists in this regard. He proposes a classification of evidence concepts of varying strength and epistemic import, and he is pretty explicit about the relationship between evidence and reasons in a way that other evidence theorists typically are not.

  2. Brian Weatherson says:

    I hadn’t realised how much had been going on in the phil-sci literature recently. That’s really helpful. Thanks Kent!!

    I should probably just read the Achinstein book myself to see this, but the bolding of ‘evidence for’ makes me wonder if the philosophers of science in question are following one of the following two strategies.

    A) Take it as given what the evidence is, and get to work on the hard philosophical question of what evidence for a proposition is; or

    B) Argue/presuppose that the interest in Williamson’s question “What is S’s evidence” rests on a kind of category mistake, and we should really be asking “What is S’s evidence for H”, for different hypotheses H.

    Both A) and B) are consistent with focussing on when E is evidence for H, rather than on when S possesses E, but they have very different philosophical implications I think.

  3. fitelson says:

    Just to follow-up on Kent’s post, I should mention that I think the Bayesianism/Likelihoodism debate has been rather ill-framed (I’ve been arguing with Elliott about this for many years now). I wrote a paper on this a few years ago — I’d be curious to hear what you (and/or your students) think, Kent. Here’s a link:

  4. antonym says:

    I know that George Smith accepts your B), Brian. To my knowledge he hasn’t published on this topic directly (although I think he’s planning to at some point in the future). He gave a series of lectures a few years ago, Turning Data into Evidence (scroll down for the text), although they are more about the role theory plays in marshaling evidence. If you’re interested, you might want to contact him – I remember him saying that while he thought he had arrived at the conclusion himself the view seemed to be growing in popularity in phil-sci of late. (This George Smith, lest there be any confusion.)

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