Reasonable Disagreement
In his recent post Robin suggests that Van Inwagen is biased in his philosophical beliefs about free will, possible worlds and the nature of persons, on the grounds that to disagree with as clever a philosopher as Lewis (rather than suspend judgement, for example) cannot be reasonable. In the paper referenced, Van Inwagen concedes that he is not arguing that any particular philosophical positions are justified, just asserting that he believes some are. Van Inwagen’s main point is in fact that the use made of Clifford’s dictum (in brief, it is always wrong to believe on insufficient evidence) is biased, since it is applied to religious belief but not to other beliefs. Nevertheless, I think we could construct on Van Inwagen’s behalf an argument for the reasonableness of his disagreement with Lewis.
Philosophers have no consensus on many important philosophical questions.
Their disagreement cannot be adequately explained on the basis of communicable beliefs (even allowing for the general underdetermination of answers to philosophical questions by the considerations available).
Therefore we must allow of there being incommunicable beliefs (which, when true, are incommunicable insights).
There is no reason to think that philosophers are irrational.
Both Lewis’s and my philosophical positions are justified with respect to their evidential bases.
We have both examined everything we know to be relevant to the question at issue.
Among the evidential base of justified philosophical belief are states that are either incommunicable insights or states we are unable to distinguish from such insights but whose content is erroneous.
What can be communicated between us has not led either of us to realise that something we took to be an insight is an error.
Therefore we can reasonably disagree.
He might also have further defended this by arguing that unless we are prepared to be accept that none of our beliefs are justified (i.e. to be a certain kind of sceptic), a similar story has to be told for all of our beliefs: that their evidential base may not be entirely communicable and the justificational relations may not be entirely transparent to us.
Nick, it seems the issue we need to consider more to further explore this topic is the appropriateness of Bayesian-like analysis. But as it is a framework intended to account for a wide range of issues in inference, we should judge it overall in terms of all of the intuitions it may or may not conflict with, relative to other possible frameworks of analysis. Since we expect some of our intuitions to be in error, finding a few conflicts with intuition should not discourage us from embracing Bayesian analysis. I invite you to take the first shot by posting sometime on what you see as the most serious problems with the Bayesian approach.
I see this is in effect being further addressed in new posts, so I’ll just answer the last two points and then leave it.Eliezer (apologies for mis-spelling your name in the last post): The answer to your challenge is in the original post, where I offered precisely such an argument. Secondly, I think you are mistaken about where the burden of proof lies. No one is disputing that sometimes there are unreasonable disagreements, which is all that your examples go to show. But you are simply assuming that Bayesianism is true. My point is that it is no less reasonable, and perhaps more reasonable, to start from the premiss that people do reasonably disagree (indeed, some would argue that we are morally required to accept that premiss), and if Bayesianism conflicts with that, so much the worse for Bayesianism.Robin: It is not that I am uninterested or unsympathetic to the formal results, but I am bringing into view ways in which it might be argued that the formal model seems to give the wrong answer. Guy brought out the point about idealisation at the end of enquiry versus our situation. There is a lot to be discussed about whether and when idealisation is a clarification rather than obscuration of philosophical issues. I have been pressing on a different point, namely the the requirement that reasons for a belief should have content that is relevant to the truth of the content of the belief. I have drawn your attention to a specific argument about endurance versus perdurance which turns on the problem of temporary intrinsics. Attending to that argument shows why Lewis thinks temporary intrinsics means perdurance is true whilst Van Inwagen does not, and the reasons that Lewis adduces are other metaphysical doctrines, in particular, doctrines about what it is to be an intrinsic property. The belief in their disagreement has no content that bears. It is quite irrelevant. If you add it as a premiss to either of their arguments it sits as an idle cog. It can neither justify nor defeat any of the reasons they adduce in this dispute. So I have given an example of the way in which disagreement, at least prima facie, has no rational significance, and your reply is to say, well yes, but in my formal model with impossible possible worlds it does. Fine, say I, so much the worse for your model!