Some time ago I offered an argument for the possibility of reasonable disagreement over philosophical positions. Brian Weatherson at TAR has just posted a paper with an interesting argument for a similar conclusion: here. He is discussing the position of Feldman, Christensen and Elga, also held by Robin and some others here, that finding an epistemic peer disagreeing with you should weaken your belief. Brian is using a strategy that is often effective at refuting a philosophical theory: seeing whether the theory can coherently apply to itself.
This equal weight view, hereafter EW, is itself a philosophical position. And while some of my friends believe it, some of my friends do not. (Nor, I should add for your benefit, do I.) This raises an odd little dilemma. If EW is correct, then the fact that my friends disagree about it means that I shouldn’t be particularly confident that it is true, since EW says that I shouldn’t be too confident about any position on which my friends disagree. But, as I’ll argue below, to consistently implement EW, I have to be maximally confident that it is true. So to accept EW, I have to inconsistently both be very confident that it is true and not very confident that it is true. This seems like a problem, and a reason to not accept EW. (Weatherson online pdf:1)
Disagreement at Thoughts, Arguments and Rants
Stuart, I think you conflating two distinct senses in which it might be sensible to judge a theory by "applying it to itself". It seems sensible that theories not be required to justify themselves, as your examples attest. But it also seems sensible to require that they not be inconsistent with themselves, which is what Leiter's on about.
I don't believe checking whether a philosophical theory can be applied to itself is a sensible way to judge it. Most proper theories have quasi-axioms that have to be asserted or taken as true. There is, alas, no inductive proof of the induction hypothesis, yet it underlies all of science.
Conversely, most theories that do justify themselves (such as Freudian analysis, which comes complete with a full justification as to why people do or don't believe it) are very highly suspect.
The philosophical theory "every affirmation I utter is true" is certainly consistent with itself; but I can't avoid feeling that it is somewhat lacking in the credibility department.