Gary Gutting has long been bothered by cases of disagreement between epistemic peers. His view, if I recall correctly, is that your judgment that an intellectual peer disagrees with you is a defeater of your justification.
This viewpoint is clearly too strong, but it raises the interesting question of when testimony generates defeaters. The Gutting view is too strong unless the kind of defeat in question is easily overridden. Suppose you and I are discussing a matter that I take myself to have thought through fairly carefully. Then the mere fact that you disagree won’t have any effect on my justification even if I believe you are my intellectual peer (you are as careful as I try to be, you are as intelligent and thoughtful, you are not motivated to hold a view more than I by irrational factors, etc.). In fact, even if you are my intellectual superior, mere disagreement won’t affect my level of justification. There’s no reason to overgeneralize from the fact that your views are generally more reliable than mine to the present case. At least, that’s what I’d tell myself until and unless you produce some piece of information relevant to the matter at hand. Such a remark sounds so strong, however, that it threatens to rob testimony of most of its power to undermine present opinion, and that would be a mistake. Thus the question how intellectual competence and testimony are related, if at all, in explaining how testimony can give one a defeater.
Here’s the view I’m tempted toward; call it the “irrelevance of competence” position. On it, information about the intellectual competence of a disagree-er is never an underminer of present opinion. In cases where it looks like such information is playing a role, it’s really something else doing the defeating. For example, if I think you are smarter than I and have thought more about the matter than I, then your disagreeing with me is a defeater. But what is doing the defeating here is my view that you know more about this issue than I.
Note that in usual cases of testimonial defeat, what matters is not degree of competence. In normal cases, such as perceptual ones, the testifier has a source of information that we lack–perhaps the testifier was present to observe and we weren’t; or perhaps we were present, but we know we don’t see as well as the other person. Or perhaps, as in auto repair cases, we have some experience with the kind of thing in question, but the other person has much more experience. In all these usual cases of testimonial defeat, some minimal level of competence is required for the testimony to defeat, but the question of intellectual parity is simply not an issue.
The strong view says this is always the case. That is, whenever it appears that intellectual parity by a disagree-er is a defeater, there is a better explanation in terms of greater knowledge or experience of the particular subject matter in question, sources of information not shared, and the like. The strong view claims that the issue of intellectual competence is simply too general to function as a defeater on its own, and that once the additional information is included that will allow defeat, epistemic parity is not itself an issue at all (though some minimal level of competence still will be).
How about disagreement by one’s intellectual superiors? I’m inclined to say the same thing here (except where one’s intellectual superior is so superior as to be infallible). As long as the person who disagrees is fallible, it should take more than an assessment of relative competence to undermine present opinion. Of course, such assessment can undermine present opinion, and rationally so, but the issue of whether such information is a defeater is the question of whether such assessment has to undermine present opinion (when no rebutters are present). There is one caveat, however. When people find themselves in a situation where an intellectual superior disagrees, humans sometimes come to distrust their own competence–this is a common experience of students (one with fairly significant implications with respect to the ethics of teaching, by the way, but which I won’t go into here). Once such trust is lost, of course, we have an explanation of defeat that does not rely on the intellectual superiority of the one who disagrees.
So, there it is: a position inviting counterexamples.