Week 5 – Kelly on disagreement

A lively discussion today of Tom Kelly’s ‘The epistemic significance of disagreement’. The presentation is here. Some thoughts follow.

It wasn’t entirely clear to us what kinds of disagreement was meant to be modelled by the proposal in the paper. Any disagreement, or only ones which persist over long periods and are resistant to resolution after lengthy discussion between peers? And are we to think of disagreement as stemming from differences in prior conditional credences (as Elga does), or from failures of logical omniscience, or from an arbitrary combination of the two? In what follows, I will assume the proposal is meant to apply to all disagreements, whatever their nature and their source, both for maximum generality, and because it will not always be clear from which source a particular disagreement stems.

We noted that the proposal didn’t generalize straightforwardly to a Williamsonian conception of one’s evidence as identical to one’s knowledge. That conception allows for an extra way in which two people could fail to be epistemic peers, in that they could have all the same credences but (due to environmental factors) have wildly different evidence. It seems that we won’t be able to rule out failures of peerhood due to this issue, so it will be even hard to identify epistemic peers if we make the identification E=K.

There was some discussion of Elga’s ‘bootstrapping’ argument in ‘Reflection and Disagreement‘ (p.15) against Kelly’s view, which Elga calls the ‘right-reasons’ view. Our consensus was that the argument simply doesn’t work – it’s not at all absurd that if you continue to stick to your ground in many cases of disagreement with a particular peer, and in fact in all those cases you had reasoned correctly and the peer had reasoned incorrectly, then you can legitimately come to consider that person no longer a peer. Of  course, this depends on appealing to a sense of ‘legitimacy’ which lines up with the notion of rationality Kelly is interested in – more on this below.

We found it a bit mystifying why Kelly initially presents the asymmetry which refutes the symmetry argument as a perspectival asymmetry. The asymmetry which really matters is surely the non-perspectival asymmetry that one agent has reasoned correctly and one has not.

The assumption that in all relevant cases of disagreement one agent is correct and one is not is a deniable one. It seems to rely on a) objective bayesianism and b) the assumption that at least one agent has reasoned correctly. So Kelly’s view is silent on what we should think if we are inclined to subjective bayesianism, or on what should happen in cases where both agents have reasoned incorrectly and reached different conclusions.

It wasn’t obvious why the right-reasons view only applies to epistemic peers, rather than to anyone who shares my evidence. Surely, if I have in fact reasoned correctly and reached the correct conclusion, then in the relevant sense I shouldn’t defer to anyone, even people who have the same evidence but have much higher degrees of epistemic virtue than myself.

Now for the main issue. It seemed plausible to us that Kelly and Elga are simply talking past each other, because they are interested in different kinds of ‘epistemic norms’.

Kelly is interested in a kind of epistemic norm which is hard to follow (to follow it in all cases we would have to know which of us and our peer has in fact reasoned correctly), but if in fact followed correctly will always lead to the epistemically best results (that is, having our credences perfectly proportioned to the evidence). Elga, in contrast, is interested in a kind of epistemic norm which we can always know how to follow. However, it is quite possible that following Elga’s norm will in some unfortunate cases actually lead us to epistemically worse results.

Suppose that we have in fact reasoned correctly about something, but we defer to many peers all of whom agree with one another and all of whom have reasoned incorrectly. Then doing what Elga advises will in fact lead to an epistemically worse result, whereas doing what Kelly advises will in fact lead to the epistemically best result. However, we will not generally be in a position to know what precise credences Kelly’s view does advise, whereas Elga’s view always gives us a recipe for our new credences.

This line of thought leads us to think that Elga and Kelly have just been talking past each other, because they are referring to different norms when they ask what we should do in cases of disagreement. Elga’s norm obeys ought-implies-can, while Kelly’s does not. Elga’s norm will not always lead to the epistemically best result, while Kelly’s will. If this is right, then we can reconstruct the disagreement between Elga and Kelly as whether Elga’s norm counts as an epistemic norm. Perhaps Kelly’s view is that Elga’s norm should not count as an epistemic norm, but at most as a purely practical norm. And perhaps Elga’s view is that Kelly’s norm is unfollowable in some cases and therefore cannot be the most explanatory candidate for a ‘primary’ epistemic norm.


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