If you’re attracted at all to relevant alternatives theories in epistemology, you’ll find some attraction in the contrastivist suggestion that some epistemic predicates are 3-place predicates. For example, you might be attracted to the idea that knowledge is best represented in terms of S’s knowing that p rather than q, instead of simply in terms of S’s knowing that p.
Here’s a question about such an approach: can this contrastivist suggestion be maintained “all the way down”? That is, if we suppose that knowledge is best represented as a 3-place relation, and we hold that justification is necessary for knowledge, can we also hold that justification is as well? If so, then we should talk in terms of S’s being justified in believing p rather than q, instead of simply in terms of S’s being justified in believing p. Furthermore, if you’re an evidentialist, you’ll want to understand justification in terms of evidence, so to go contrastivist all the way down will require making sense of the idea of something’s being evidence for p rather than q, but not evidence for p rather than r (making, of course, the entirely reasonable assumption that what is justified is a function of the quality of one’s evidence).
I’m not sure, however, how to understand the idea of something’s being evidence for p rather than q.
I can make sense of the idea if we explain it in some way to 2-place predicates. For example, if we try to clarify the nature of evidence in terms of the language of probability, the view isn’t 3-place all the way down. The best we could say is that p is more probable on e than q is, or we might compare likelihoods here, comparing the probability of e on p with that of e on q. Each of these approaches is a comparison between two 2-place predicate claims, not a 3-place predicate claim. (I believe this point applies to Sober’s idea of constrastive confirmation, where some evidence confirms p as opposed to q, since this three-place relation is defined in terms of likelihoods.) The same happens if we clarify evidence for p rather than q in terms of what rules out q but leaves it open whether p, and if we use Schaffer’s language of what one has proven rather than presupposed: we’ll get a relation between premises and conclusion for what is proven, not some three-place relation. So in all these cases the fundamental epistemic notions will not be three-place relations.
If we suppose that the fundamental notions will not be three-place notions, is this a problem? It’s not obvious if it is, but here’s a thought. If the basic notions are at least one place less than contrastivists hold is true of other epistemic notions, why does the additional place enter into the picture? For example, suppose that the fundamental notion is e’s being evidence for p. Then we can define a notion of justification in terms of the totality of one’s evidence constituting evidence for p. And from there, it looks as if we can extend the account to one of knowledge, as long as p is true, believed, and one’s justification ungettiered. Where in this story does the need for a third relata enter? If there is no good answer here, we should want contrastivism to be three-place “all the way down.”