Let’s say that the mentalist about evidence believes the following supervenience thesis:
M: Necessarily, if A and B are in the same non-factive mental states from the cradle to the grave, A and B will share the same evidence from the cradle to the grave.
Here’s an argument against mentalism, so understood:
(1) We have non-inferential knowledge of the external world.
(2) If we know p non-inferentially, p is part of our evidence.
(3) If ~p, p is not part of our evidence.
(4) It is possible for someone to be in just the same non-factive mental states as any one of us and believe mistakenly that p.
(5) We know p non-inferentially.
(C) It is possible for someone to be in just the same non-factive mental states as any one of us and while p will not be part of their evidence, p will be part of ours.
Let’s bracket (1) for now. I think Feldman and Pryor do a nice job defending the claim that we could have such knowledge. No point in conceding (1) but denying (5). Let’s bracket (4) for now. I don’t think anyone was going to take issue with it. Now our question is this: should the mentalist deny (2), (3), or both? I think these should the yadda yadda yadds deny blah blah blah claims are funny, so let me rephrase. What plausible responses could the mentalist offer in response to the argument apart from the table hammering response that says that it is just intuitively obvious that (C) is false. If you don’t like the argument, that’s fine, but a diagnosis is what I’m looking for.
In his paper in the new volume on Williamson, Goldman suggests that our evidence will consist of the contents of our non-inferentially justified beliefs. I’ve seen similar things suggested by a number of people. Since no one seems to like the view that says there are no false, justified beliefs (apart from Sutton and myself), the view that Goldman is proposing as an alternative to Williamson’s appears to be a view that denies (3). Williamson remarks that on this sort of view:
it is not even clear that one’s evidence must be consistent, let alone true … there are grave difficulties in making sense of the evidential probabilities on inconsistent evidence, since conditional probabilities are usually taken to be undefined when conditioned on something inconsistent. In particular, any proposition has a probability 1 conditional on itself and any contradiction has probability 0 on anything … but these constraints cannot both be met for probabilities conditional on a contradiction” (2009: 310).
For obvious reasons, those of us who think that justified beliefs are factive will not think that the propositions you justifiably believe form an inconsistent set of propositions but those who deny this will have a harder time denying that it’s possible for someone to justifiably believe inconsistent sets of propositions. The questions then are these. If you deny that evidence is factive, what view do you adopt to rule out the sort of case that worries Williamson? Is it a big deal if you adopt a view of evidence on which evidential probabilities are undefined?
It seems that we have the beginning of an argument for the factivity of evidence. Let me add to the evidence for factivity. Consider:
(6) There is a reason for him to think he has a flu; namely, that his doctor told him he has come down with a flu.
The following just sounds contradictory:
(7) There is a reason for him to think he has a flu; namely, that his doctor told him he has come down with a flu. Having said that, his doctor didn’t tell him that.
Obvious explanation: claims of the form ‘There is a reason for him to believe p; namely, that q’ entail, inter alia, q. Maybe there’s some subtle difference between reasons to believe and bits of evidence, but it’s not as if things get better if we use evidence-talk instead of reasons-talk:
(8) What’s his evidence for believing that he has a flu? That his doctor told him that he has come down with a flu. Having said that, his doctor never told him that he had a flu.
You can say, ‘Well, but his evidence really will be a mental state of some sort he could be in even if his doctor hadn’t spoken to him or some fact about such a mental state’. You can say that (6) is really just elliptical for some longer description of mental facts that would be true whether the subject was hallucinating, dreaming, or veridically perceiving. Okay, but that’s just using Factivity and mentalism to redescribe the evidence in terms of truths related to but distinct from those I say are entailed by (6). Things don’t get better when you say:
(9) What’s his evidence for believing that he has a flu? That he seemed to hear his doctor tell him that he has come down with a flu. Having said that, I should note that it never seemed to him that his doctor said this.
Finally, think about the role that evidence plays in inference, such as inference to the best explanation. Suppose you know that p is part of your evidence. (Note: I didn’t say, ‘Suppose you know that p is true’). Question: is there something further you need to know in order to know that it is either a brute fact that p or there is some explanation for p? Intuitively, it seems to me that anyone who knows that p is part of her evidence is thereby in a position to know that either there is an explanation for p or p is a brute fact. The first disjunct entails p. If you know there’s some explanation for p, you know there’s some true statement of the form ‘p because q’, and we know that ‘p because q’ entails that both p and q are true. The second disjunct entails p. You know that ‘It’s a brute fact that p’ entails p. So, you know that if p is part of your evidence, a disjunction that entails p is true. So, you know that if p is part of your evidence, p is true. I can’t see how that could be unless p’s being evidence requires, inter alia, that p be true.
Those who deny factivity I think have to say that when you know that p is part of your evidence, you could still fail to be in a position to know whether the question ‘Why is it that p?’ rests on a mistake. (The question ‘Why do we lose weight when we die?’ rests on a mistake because the answer is ‘We don’t’ and I’m saying that once you know that p is part of your evidence, you no longer have to worry whether the question ‘Why is it that p?’ rests on a mistake.)
Knowledge and Possession
According to (2), you don’t need more than non-inferential knowledge of p’s truth to acquire p as part of your evidence. We can call this ‘IKSE’ for short (it’s short for immediate knowledge suffices for the possession of evidence and probably contains lots of stuff that you won’t need but couldn’t hurt). Suppose S knows p non-inferentially. One possibility is that p isn’t the sort of thing that could be evidence. Is that because evidence can’t be a proposition or fact? Maybe, but let’s assume that evidence is propositional just for fun. I take it that most of Williamson’s critics aren’t criticizing him simply on the grounds that they don’t think evidence is propositional. If evidence are the thoughts (true or false) that you have in mind, p will be in mind when you know p non-inferentially. If evidence consists of facts or true thoughts/propositions, we don’t have to worry about whether p since it is known to be true. So, maybe the worry about IKSE is this: there’s more to possessing a piece of evidence than knowing non-inferentially that the proposition that constitutes evidence is true.
Okay, so suppose we talk about reasons for belief. If you know p non-inferentially and know q to be a deductive consequence of p, can’t we say that you have a reason to believe q because you know p non-inferentially? I think so. Aren’t you being awfully picky about evidence if you say that I’m ignoring the all important distinction between reasons for believing that explain why a belief is justified and evidence proper?
When I see the sorts of things that get floated as platitudes about evidence, it seems that _things we know non-inferentially_ fit these platitudes. If our evidence is that which we have to go on in trying to settle a question, you clearly _can_ go on the things you know non-inferentially. Maybe the platitude is really that evidence is that which we can properly rely on in theoretical deliberation. Okay, is it _improper_ to rely on p when you know p without needing to know anything else? If it is improper to rely on p for the purposes of theoretical reasoning where the impropriety is epistemic, that should affect the justificatory status of the belief in p. That would seem to prevent the belief from constituting knowledge. Wait, have we just hit upon an argument for IKSE? If you are non-inferentially justified in believing p, it cannot be epistemically improper or impermissible to rely on p in theoretical reasoning. So, there are no counterexamples to IJSE, the claim that if p is a piece of evidence and you are non-inferentially justified in believing p, p is part of your evidence. No counterexamples to IJSE means no counterexamples to IKSE because IJSE entails IKSE! Fantastic.
I think there’s a decent case to be made against mentalism, but I could be horribly mistaken. Yes, I realize that the data is complicated. I’ve never claimed that there’s no evidence against Factivity and I’ve never claimed that there’s no evidence against IKSE. But, there are arguments that suggest that that evidence is misleading. Are they any good?
Late addition. I was eating a taco (yes, it was delicious!) and I realized I forgot to post something that I’ve been thinking about lately that I think is interesting. If I try hard enough, I can make myself think it is related to Greg’s question below.
In the post, I mention an argument for factivity that focuses on the role that evidence plays in explanatory inferences. The example I had in mind was that of non-normative explanations of observational evidence. I gather some evidence by means of observation. If know that p is part of my evidence, I know that p is either a brute fact or an explanandum for which I should find an explanans, explanandum and explanans propositions are true, the same is true for brute facts, logic, and factivity. What about normative explanations? Here, I have in mind claims of the form ‘You shouldn’t believe p because q’. Now, I think that when I know that q strongly disconfirms p and know that q is part of my evidence, I can often say things like this that are true. This seems very much in the spirit of evidentialism. But, it seems that ‘You shouldn’t believe p because q’ entails both ‘You shouldn’t believe p’ and ‘q’. So, while I think that evidentialists will want say that it is evidence that explains the epistemic oughts and shoulds, there is some linguistic evidence that suggests that they are on the hook for accepting the factivity of evidence that derives from the factivity of explanations.