Disagreement, Evidence, and Perception (DRAFT: PLEASE DON'T QUOTE OR CIRCULATE WITHOUT PERMISSION; COMMENTS APPRECIATED) Thomas D. Senor The University of Arkansas Section I: Introduction The question of what rationality requires when you find that someone equally as intelligent and informed disagrees with you on a given topic has lately received a great deal of attention. As with many philosophical issues, what makes this matter so interesting is that there are very plausible cases to be made for opposing views. For example, many of the topics that we care deeply about (religion, morality, and politics, to name a few) are hotly contested even by people of sharp mind and upright character. This strongly pushes us (initially anyway) to think that of course reasonable disagreement among peers is possible: indeed it is not only possible but actual and widespread! On the other hand, if you start not with what you take yourself to observe but with epistemic principles, you can be led to think that appearances are deceiving. Here is a line of reasoning that begins with a plausible epistemic principle and concludes that reasonable disagreement is not possible: a given set of evidence cannot both support a proposition and its negation; that is, evidential relations are determinate and objective-they are not relative to persons or circumstances. So if an epistemic peer and I share a set of evidence, and on the basis of that evidence I believe that P and my peer believes not-P, at least one of us is wrong not only about P but also about what the evidence supports; and since neither of us has any independent reason to think that he is right and the other is mistaken, rationality requires both of us to suspend judgment. 2 So what to do? Should we believe what reason teaches or our (potentially lying) eyes? There are three fundamentally different ways of responding to this problem. First, one might side with our initial epistemic scruples: in cases of disagreement after disclosure, you'll be unreasonable if you "stick to your guns." You should not give privilege to a belief simply because it is yours. This view has been dubbed "The Equal Weight View" and seems to be the majority opinion.1 In contrast with this is the perspective that advises you to hold fast in the face of disagreement.2 While the previous view has been thought to suffer from spinelessness, the present perspective (dubbed by Thomas Kelly as the "Extra Weight View") can seem unreasonably dogmatic. The third position claims that when you discover peer disagreement what rationality requires is largely determined by how you responded to the evidence in the first place. If the initial evidence supports your view, then while the fact that a peer disagrees should cause you to modify your credence to an extent, you should soldier on (albeit with a bit less spring in your cognitive step). On the other hand, if you've done a poor job appreciating the evidence, then disagreement should push you considerably in the other direction and you should give up your belief (which you shouldn't have had in the first place).3 Even if reflection alone is insufficient for making it clear whether you've been true to the evidence, it's fealty to what your grounds support that matters.4 Following Kelly, we'll call this the Total Evidence View (TEV). In this paper, I will be concerned to defend a modified version of the third position. As we will see, I believe there is a broad range of cases that are generally thought to be the bread and butter of the Equal Weight View that do not support it as well as has generally been supposed. While Kelly has also argued that his favored version of the TEV can support the "intuitive" reading of these cases, my contention will be that this is a mistake and that the proper view to take of these cases, both intuitively 1 See Feldman 2006 and 2007, Christensen 2007, and Kornblith 2009 2 See Foley 2001 3 If one makes the uniqueness assumption, then at most one of you should (more or less) stick to your guns. But if the uniqueness assumption is wrong, then it might be that both of you have responded adequately to the evidence and so each of you should (mostly) soldier on. 4 See Kelly 2005 3 and theoretically, is rather the opposite of what both Kelly and Equal Weight proponents have claimed. Along the way we'll discuss the epistemic significance of perceptual evidence and I'll argue against a primary commitment of those who favor the Equal Weight View (i.e., the Uniqueness Thesis). As we will see, the perspective I'll argue for has some interesting consequences for the epistemology of religious belief that it doesn't have for moral and politic belief. Nevertheless, once confidence in the Uniqueness Thesis is shown to be misplaced, we can see that reasonable disagreement is possible regarding our philosophical and political beliefs as well. I'll begin by quickly canvassing some of the cases that have received the most attention and on which there is mostly agreement. My contention in this section is that these cases do not speak with the single voice they are often heard to speak with and that their support for the Equal Weight View is grossly overstated. Section II: Perceptual Cases In an early paper ("early" only by the standards of the disagreement literature) Richard Feldman presents the following case and couples it with a prescription: Suppose that you and I are standing by the window looking out on the quad. We think we have comparable vision and we know each other to be honest. I seem to see what looks to me like a person in a blue coat in the middle of the quad. (Assume that this is not something odd.) I believe that a person with a blue coat is standing on the quad. Meanwhile, you seem to see nothing of the kind there. You think that no one is standing in the middle of the quad. We disagree. In isolation-before we talk to each other- each of us believes reasonably. But suppose we talk about what we see and we reach full disclosure. At that point, we each know that something weird is going on, but we have no idea which of us has the problem. Either I am 'seeing things' or you are missing 4 something. I would not be reasonable in thinking that the problem is in your head, nor would you be reasonable in thinking the problem is in mine.5 Something "weird" is going on, indeed. It is curious that Feldman would use an example so bizarre when more straightforward cases would make his point more forcefully. But for the moment, let's think about the case Feldman describes. Apparently, both parties (call the one who sees the person in the quad 'Rich' and the one who doesn't 'Earl') have an unobstructed view of the quad, the lighting is fine, and the quad is not packed with people (otherwise they would both believe that there was someone in the middle of the quad, even if they disagreed about who is there). In fact, Earl doesn't see anyone in the quad and Rich seems to see the person in the blue coat. So either Rich is simply hallucinating or Earl is suffering a significant visual malfunction. Feldman thinks that both Rich and Earl should withhold belief because it would be unreasonable for each to think that the problem is with the other person. I think this diagnosis is incorrect. First, when I put myself into this case (regardless of perspective), I have a hard time taking what the other person is saying seriously. It is more reasonable to believe that the other is messing with me than that either of us suffers from a major visual problem. Were I either Rich or Earl, I'd be convinced that there was a joke that I'm not in on; I wouldn't be able to take the other's claim seriously. But this is cheating, I suppose. The disagreement cases are supposed to be cases in which the sincerity of the report of both parties is beyond dispute. So let's put aside the first point and assume that each peer takes the other's report at face value. Let's make the case particularly thorny. Rich and Earl are old friends who have spent a lot of time together and know each other to be trustworthy and reliable generally. But now they have this remarkable difference of opinion about they see. What should they do? The Equal Weight View, it is said, gives a clear ruling: Rich and Earl should each give up his previous belief and both withhold. For while each has evidence that, in isolation, would make his 5 Feldman 2006, p. 223 5 original belief reasonable, once he learns of the other's contrary belief and that it is based on what is apparently visually apparent, then he has no rational reason to prefer his own belief to the other's. It's not clear to me either that the Equal Weight View has this implication or that, for whatever reasons, the ruling that both sides should withhold is correct. For even fans of the EWV don't think that every disagreement with a peer is cause for belief suspension. Rather, it is disagreement in cases of shared evidence that call for splitting the difference. And it is surely not the case that Rich and Earl have the same evidence in the crucial respect. This is so for two distinct but related reasons. First, even if it were true that, prior to learning of their conflicting beliefs, Rich and Earl had the same evidence, once they disclose each will expand the evidence pool in a way that will have them coming apart. When, for example, Rich learns that Earl doesn't see the man in the quad, he acquires a defeater for his belief that there is a man there.6 In particular, he acquires a reason to think that he is suffering vision problems, and that his evidence might not support his belief as well as he thinks. So he should reflect in an effort to see if he has any independent reason to think that he's right and Earl is wrong. And if he's thoughtful, he'll be able to come up with something. After all, Rich has a long and intimate history with his own visual processes that he lacks with regard Earl's. Rich, it seems to me, should reason as follows: I'm having a clear sensory experience as of seeing a person in a blue coat in the middle of the quad. Introspectively, everything seems normal. When I form beliefs like this in this kind of context, I'm virtually 100% reliable. Were it not for the fact that Earl doesn't see this person, I'd have no doubt at all that I'm right. While I've always known Earl to be as reliable as I am with regard to standard perceptual beliefs, I don't have the same kind of history with his perceptual beliefs that I have with mine. I also don't know 6 More will be said shortly about the defeaters and disagreement. 6 if things really seem perfectly normal to him. He says they do, but without experiencing what he's experiencing, I can't be sure. So my evidence favors my belief over his. Earl would be reasonable in engaging in a parallel refection. Each of these lines of thought is perfectly appropriate. Notice that the degree of confidence each has in his respective belief should be muted to some extent-that a person you know to be generally reliable and trustworthy disagrees with you about something apparently obvious as this is cause for concern. But it hardly follows from this that rationality requires that one go from having fully-confident belief (as one would have had sans disclosure) to withholding the proposition in question. Compare this case with another. Randy calls you to say that he has just been in an accident in which your mutual friend Diana was driving. Randy says that Diana ran a red light and was broadsided. No sooner does your conversation with Randy end when you receive a call from Gary who says he has just been in an accident in which your friend Diana was driving and that she was going through a light that was clearly green when another car t-boned them. Both Randy and Gary mention that the other was a passenger in the car. Now somebody's got it wrong. While you'd have been reasonable in accepting either's testimony in the absence of that of the other, now that you've heard them both you are in a predicament. Given that you know each testifier to be trustworthy, and that each has confidently expressed his contrary opinion, you should suspend belief about Diana's culpability in the accident. Now let's change the scenario. Put yourself in the car with Randy and Diana. Just before the accident, you happened to look up and as a result you had a clear percept of a green light. After the accident, you discover that Randy thinks the light was red. What should you do? Here's your evidence: you have a clear percept of a green light and a belief that a peer thinks you are wrong. What you know of your own situation is that you have a strong memory impression of a clear percept of a green light. You know that Randy claims to have had a clear percept to the contrary but you don't have access to 7 that. Even if you believe Randy to be sincere in his report you aren't in a position to verify that his percept was as he thinks it to be. So the evidence you have at your disposal is importantly different from the evidence that Randy has: he has his own percept/memory impression and belief about what you report, and you have your very distinct percept/memory impression and belief about what Randy reports. Since the two of you do not share the same body of evidence, it is unclear that the Equal Weight View implies that you should each suspend judgment. For if the weight of the evidence we each possess falls to the differing beliefs we take, then we are each reasonable in believing as we do even on the Equal Weight View. So I think the first lesson to be gleaned from the case of perceptual disagreement is that it is a mistake to think that there is a shared pool of evidence between the two conflicting subjects and if the evidence varies substantially (and if the parties both know this) then there is no good reason to insist that rationality requires mutual withholding. In the spirit of the Equal Weight View, one might object to what I've just argued as follows: yes, Rich and Earl have somewhat different sets of evidence but that difference is hardly "substantial" given that each knows the other disagrees. For the fact that a peer who is positioned equally well to ascertain a perceptual truth not only fails to believe as one does but in fact holds a contrary belief is epistemically weighty enough that it swamps the reasonability of the initial beliefs even if those beliefs were based on different sets of evidence. The fact that it perceptually seems to Rich that there is a man in the quad isn't good evidence for there being a man there if Earl is standing next to him and reporting a perceptual experience that is inconsistent with it. The answer to this objection to my first point about the perception cases leads me to my second point. To see it, let's focus on Rich. He has a standard, vivid perceptual experience of seeing a man in the quad. In isolation, his belief is unquestionably reasonable. Then he talks to Earl. As a result of their conversation, Rich acquires a defeater. The defeater is grounded not in perception (although of course, 8 perception is at work here too) but in testimony. So Rich has a perceptual reason to believe that there is a man in the quad and a testimonial defeater. Earl's position is the reverse. As John Pollock has taught us, defeaters come in two varieties: rebutting and undercutting. A rebutting defeater for P is a reason for thinking that P is false; an undercutting defeater is a reason to think that it's not the case that the belief is likely to be true given the way the belief was formed or given the evidence upon which it is based. Which kind of defeater does Rich get when Earl tells him what he believes? The answer is "both." For the fact that a reliable person testifies to not-P is reason to think not-P is true. After all, Rich would take Earl's testifying that he has a clear perceptual belief that not -P as a very good reason to believe not-P were Rich not around to see for himself. That shows that Earl's testifying to that now gives Rich reason to believe not-P and hence that it serves as a rebutting defeater.7 The way disclosed disagreement among peers has been treated in the literature, however, is generally as an undercutting defeater. Finding out that a peer with the same evidence draws a conflicting conclusion has been understood as providing "higher-order evidence." I now have evidence that my original evidence doesn't support my belief as well as I thought it did. Let's consider each of these types of defeaters and see what the net effect is of adding either or both kinds to the evidential pool. And because of the bizarre nature of Feldman's quad example, let's focus instead on the accident case and stipulate that Randy really did have a clear red-light percept and Gary a clear green-light percept. What should each do when he learns of the other's belief? One point that should be noted here is that, strictly speaking, what is important is not actually the belief of the other person but the fact that the other person has testified to believing it. As long as Gary has no reason to doubt the sincerity of Randy's assertion that the light was red, the damage to Gary's reasonability for believing that the light was green will be done even if it should turn out that 7 Thanks to Jack Lyons for pointing out to me that, contrary to the way the discussion has gone in the literature, one's learning that a peer disagrees gives one a rebutting (as well as potentially undermining) defeater. 9 Randy is lying. So standard cases of peer disagreement are cases in which one comes across a testimonially-based defeater for an otherwise reasonable belief; whether the testifier actually has the conflicting belief is inconsequential. Should Gary take Randy's testimony to be a rebutting defeater? This much is clear: there is epistemic damage done to Gary's belief that the light was green. For, as noted, in the absence of Gary's green-light percept, Gary's testimony that the light was red would be sufficient for Randy's coming to believe reasonably that the light was red. The question, then, is not whether there is epistemic damage done but what its extent is. I take the damage to be significant and that it reduces the rational credence level of Gary's belief. But should Gary now withhold? I don't think so. For there is not much that is better evidence than a clear percept in good conditions of observation. And Gary's total relevant evidence consists of such a percept and testimonially-based belief to the contrary. Gary should continue in his belief (albeit with reduced confidence) not because he arbitrarily favors his belief over Randy's but because perception is epistemically weightier than testimony. This isn't to say that perception can't be swamped by testimony: should he be on a bus with fifty people all of whom claim to have seen that the light was red, then he should change his belief. But the evidential strength of a clear percept is, it seems to me, sufficient to make it reasonable for a person to continue believing despite a single case of contrary testimony. The above has assumed that disagreement provides a rebutting defeater and I've argued that while it does some epistemic damage (to the point where one should adjust one's credence level downward a bit) one is nevertheless reasonable in continuing to believe as one originally did. But I noted earlier that cases of disagreement are often seen as providing an undermining (rather than rebutting) defeater. So, does Randy's testimony provide Gary with good reason to think Gary's evidence doesn't support the belief that is grounded in it? This is more complicated but a good case can be made for 10 thinking that it does not: for a clear percept of a green light is surely good evidence of a green light. Is it good reason to think that in this particular case the evidence of the green light percept is misleading? I don't think it is that either. How is it that, in good perceptual conditions, a clear percept of a green light is not good evidence that the light was green? Disagreement is importantly different from the standard kinds of perceptual underminers. For example, if I have a clear green object percept while looking at a display in a museum and then learn that the object is illuminated by green light, I thereby acquire an undermining defeater. In this case, the object's looking green is not a good indication that it really is green; or if I learn I've been slipped a drug that makes non-green objects appear green, then again, my seeming to see something green-my having a clear, green percept-is not a good reason for me to think the object really is green. But in the case at hand, Gary's learning that Randy disagrees with him about the color of light doesn't provide him with good reason to think that, in this circumstance, seeing a clear, green percept is not a good reason to think the light is green. In fact, he should continue to think that, if he had a clear, green percept, then the light was very probably green. So if it doesn't give him a good reason for thinking that having a clear, green percept is not good reason for thinking that the light is green, and it doesn't provide him with a good reason to think that in this particular circumstance there is not a reliable connection between such percepts and green lights, then does it have any undermining effect at all? Yes, it does, at least in the case of Gary and Randy. Each now has a reason to think, not that their evidence is misleading but rather that they don't have the evidence they thought they had. Each believes that his belief is grounded in an unequivocal perceptual experience that supports his belief. Finding out that a peer who was positioned to have the same visual experience you had claims that he didn't is some reason to wonder if you had the experience you thought you had. It's a reason for doubting that things were as you seem to recall them being. Now as we noted with rebutting defeaters, a proposition can have some undermining effect without making it the case that, on balance, the prima facie reasonability of the belief is defeated. For 11 example, suppose instead of learning that I had been given a drug that will definitely make me hallucinate green objects, I'm given a drug that has that effect five percent of the time. My belief that the object I see in the museum is green is less reasonable than it would have been had I not been given the drug but it is ultima facie reasonable. I think much the same should be said about Gary's and Randy's beliefs. Learning that the other has a belief that conflicts with his own is both some evidence that his belief is false and some reason to think that perhaps he doesn't have the evidence he thought he did, but neither is sufficient to override the significant perceptual evidence that each takes himself to have. The point here, and one that will get discussed much more presently, is that the evidential significance of perception is great. In particular, the kind of perception that is especially evidentially weighty is what we might, following Descartes, call "clear and distinct" perception. Although I'm using Descartes' term, I mean something different by it-something I can't adequately define but can point to and that should be enough for our purposes. Suppose you are in the garden in the middle of the day looking at a red rose from the distance of a few feet. Nothing obstructs your view: the rose bush with its bright red flowers and deep green leaves fill your visual field. Here's a second example: you are standing by the piano listening to a rousing version of The Maple Leaf Rag. Your hearing is fine and there is nothing competing with the sound of the piano. These are paradigms of clear and distinct perception. Something less paradigmatic but still within the scope of what I have in mind is when you are sitting at a traffic light waiting for the change from red to green. You watch the light intently waiting for your turn to go. When the light becomes green, you see it clearly and distinctly. More on the importance of clear and distinct perception will come in the next few sections of this paper. 12 Section III: Simple Inference Cases David Christensen provides us with a different kind of case that is supposed to provide intuitive support for the Equal Weight View. Below is his presentation of the case followed by what he thinks rationality prescribes. Suppose that five of us go out to dinner. It's time to pay the check, so the question we're interested in is how much we each owe. We can all see the bill total clearly, we all agree to give a 20 percent tip, and we further agree to split the whole cost evenly, not worrying over who asked for imported water, or skipped desert, or drank more of the wine. I do the math in my head and become highly confident that our shares are $43 each. Meanwhile, my friend does the math in her head and becomes highly confident that our shares are $45 each. How should I react, upon learning of her belief? I think that if we set the case up right, the answer is obvious. Let us suppose that my friend and I have a long history of eating out together and dividing the check in our heads, and that we've been equally successful in our arithmetic efforts: the vast majority of times, we agree; but when we disagree, she's right as often as I am. So for the sort of epistemic endeavor under consideration, we are clearly peers. Suppose further that there is no special reason to think one of us particularly dull or sharp this evening-neither is especially tired or energetic, and neither has had significantly more wine or coffee. And suppose that I didn't feel more or less confident than usual in this particular calculation, and my friend reports that she didn't either. If we set up the case in this way, it seems quite clear that I should lower my confidence that my share is $43 13 and raise my confidence that it's $45. In fact, I think (though this is perhaps less obvious) that I should now accord these two hypotheses roughly equal credence.8 I have no interest in contending either of Christensen's claims here: surely, the fact that my peer has come up with a different number is reason for me to be considerably less confident than I originally was in my answer, so much so that, for the moment, I should probably just suspend belief. What interests me, however, and what doesn't get discussed by Christensen, is what I should do if I carefully recheck my figures and come to the same conclusion. I take it that even the friend of the Equal Weight View will grant that if I do this and I don't yet know the outcome of my peer's reevaluation, I am again reasonable in my original belief. For now my evidence includes the fact that careful rechecking led me to the same number and that will tip the scales in my favor. However, suppose my peer reports that after careful checking, she reconfirmed her figure too. What should we do then? The answer depends on details of the case that have yet to be specified. Let's distinguish two possibilities. Case One: both times I ran through the figures, I do the math in my head in a way that seems to me a little fuzzy. I'm having trouble not being distracted and while I'm generally reliable even in these contexts, I recognize that my now making and repeating an uncaught mistake would not be surprising. Case Two: both times I ran through the numbers, each step in my reasoning, and the transitions from one step to the next, seem completely clear to me. Were it not for the fact that my peer disagrees with me, I would be extremely confident that my answer was correct and the strength of my conviction would be reasonable. Case One is akin to a perceptual peer disagreement when one doesn't get a clear look at the object in question. We are hiking in the woods and a large animal quickly crosses the trail in front of us and disappears into the woods. We are both avid hikers and can visually distinguish deer from elk when we can see the animals clearly. But this happened quickly and neither of us got a particularly good look 8 Christensen 2007, p. 193 14 at the animal. I think it was an elk and that would be reasonable for me to believe were it not for your telling me it was a deer. Because of the fuzziness of our respective percepts, we each have relatively meager evidence for our respective beliefs and so disagreement is sufficient for defeating the reasonability of our beliefs. In version one of the restaurant case, we have something epistemically very much like a case of unclear vision, and as with the perception case, disagreement is sufficient to override the relatively meager evidence we have. Case Two, on the other hand, is something different and is much closer to clear and distinct perception. In the original case, five of us are splitting the check evenly and I think our shares are $43 each. When I learn that my peer thinks it's $45, I'll do the following: I'll multiply five times forty-three in my head ((5 x $40 = $200) + (5 x $3 =$15) for a total of $215) and then look again at the total bill. If the bill is exactly $215, then I'll have confirmation that I'm right. Notice that the three-step process that leads me to the total of $215 consists of very simple arithmetic. In many circumstances, one with even minimal mental-math skills can clearly see that each step is correct. In a case like this, then, when I've done my recheck and can distinctly see that my answer is correct, the defeating effect of my peer's disagreement is very minimal. I'd say that my level of confidence here should be what it would be if I were seeing that the animal standing in plain view before us is clearly an elk even though you say it is a deer. If, after hearing your opinion, I take a second look at the animal, see the presence of the distinguishing elk characteristics and lack of deer markers, I will be reasonable in sticking to my guns. What both the perceptual and inferential cases have in common is this: to the extent that one can clearly and distinctly perceive the object in question or the truth of the proposition or the holding of an inferential relation, is justified in continuing to believe (at least for the most part). But if one's percept is equivocal or one's inferences are not suitably transparent, then peer disagreement provides significant defeat simply because of the equivocal nature of the evidence. As I said before, when the 15 clash is between a perceptual belief grounded in a clear, distinct percept and a testimonial belief, perception is to be preferred-not because it is my perception but because it is perception. Why should this be? That is, why is perceptual evidence more significant than testimonial evidence? And more significant how? The next section will discuss the answers to these questions. Section IV: The Evidential Import of Perception, Part I In ruling on the examples above, I claimed that in cases in which the subject's belief is grounded in a clear and distinct perception, she is reasonable to continue with her original belief even if a peer who is apparently situated in an epistemically-equal manner disagrees with her. The reason I gave for this was that perception is evidentially weightier than testimony. There are two independent reasons why this is so: perception is more trustworthy than testimony and it is a qualitatively better form of evidence. The trustworthiness of perception: perception is worthy of our trust because it is generally very reliable. To this I must make two immediate caveats: First, there are contexts in which perception is not reliable, and inasmuch as we know what those contexts are, perception is not trustworthy there. If one has good reason to think one is in such a context, then one shouldn't believe what one seems to perceive even if there is no disagreement. If one has good reason to think one might be in such a context and there is peer disagreement, then even if a belief would have been reasonable apart from disagreement, it ceases to be reasonable after disclosure. My second caveat is that I will here be making common sense assumptions about the reliability of perception: I will not offer any argument for this claim (nor am I aware of a good argument for it). 9 But we all think that when, for example, our eyesight is functioning normally in good light and we see a medium-sized object in close proximity, we are reliable in the beliefs we form regarding its perceptual 9 See Alston 1993 for an extended argument that there is no way to demonstrate the reliability of sense perception. 16 properties. The better look we have at the object and the more attentive we are when we perceive it, the more reliable we are and the more trustworthy our belief is. One reason for taking perception to be more trustworthy than testimony is that most cases of testimony will trace back to cases of perception both regarding the speaker and the hearer.10 Regarding the latter, the only way for one to become aware of the testimony of another is via perception. And the vast majority of what a testifier testifies to she has learned from perception. Unless she is reporting simply on what she's introspecting or what she takes herself to know a priori, the content of her testimony will be grounded in what she's experienced through the senses. Assuming that testimony is not typically about the a priori or the conscious contents of our minds, our testimony can be at very best only as trustworthy as perception is. But we can see that in practice it would be shocking if it were anything close to as reliable. Take a very simple case: you see our mutual friend Ted at the mall and report to me that you saw him there. My eventual belief that Ted was at the mall depends upon (i) the sincerity of your report, (ii) the reliability of your sense perception, (iii) your ability to articulate what you saw into a language I can understand, (iv) my ability to make sense of the words you utter in this given instance, and (v) my ability to fix belief accurately on what I can make sense of. Now even if we suppose that some of these steps are extremely highly reliable, it is clear that if we are to compare the evidential value of my clearly and distinctly perceiving that Ted was at the mall with my coming to believe it on the basis of your reporting it to me, I have much greater reason to trust my senses than to trust the belief that I form on the basis of my interpretation of your report. Notice that the above point is entirely independent of the reductionism/anti-reductionism debate in the testimony literature. For whether testimony is epistemically basic or not, the likelihood that any given instance of testimonial belief is true will depend on the various aforementioned factors. 10 I'll often use the word "hearer" when speaking of the person who receives the testimony but this should be taken as shorthand for "receiver" or "consumer"; it's not meant to imply that all testimony is communicated via speech. 17 Anti-reductionists will have to grant that not all basic processes are equal when it comes to trustworthiness; and there is no good reason for them to refrain from making this point. So one reason to put more stock in perception than in testimony is that the former is more worthy of our trust. However there is a second important reason for preferring perception that, while perhaps in some way related, is also importantly distinct. We can start to get a handle on the superiority of perception by considering a couple cases. First, though, let's look at what one might think if one takes perception and testimony to nearer epistemic sources than I am claiming they are. In Kelly 2009, Thomas Kelly considers the epistemic impact of 'higher-order evidence'-that is evidence about how good one's evidence is vis-à-vis a particular proposition. Kelly calls first order evidence "non-psychological evidence" and evidence about whether other people agree or disagree with one regarding a proposition, "psychological evidence." He writes that, As more and more peers weigh in on a given issue, the proportion of the total evidence which consists of higher order psychological evidence increases, and the proportion of the total evidence which consists of first order evidence decreases. As the number of peers increases, peer opinion counts for progressively more in determining what it is reasonable for the peers to believe, and first order considerations count for less and less. At some point, when the number of peers grows large enough, the higher order psychological evidence will swamp the first order evidence into virtual insignificance.11 I have no wish to deny that this can happen. Take a variant of the restaurant case in which the diners don't agree to split the check separately and five of them race to see who can first figure out what each owes. The person who finishes first should probably not have great confidence in her results; after all, these are more complicated computations done more hurriedly than in the original case. But with each added report of other diners whose numbers match those of the diner who first reported her results, 11 Kelly 2009, page 34. 18 the epistemic situation of the group improves. Eventually, it's fair to say, the testimonial evidence (what Kelly calls "psychological evidence") comes to outweigh the original evidence since the chances that they could all be wrong is quite low even though the chance of error on the part of any of them individually was quite significant. Yet there are other cases where no swamping occurs. Suppose you are at Busch Stadium in St. Louis watching the Cardinals play. As he so often does, Albert Pujols hits a home run, bringing 45,000 people to their feet. From your seat you have a clear view of Pujols' swing and of the ball as it sails over the wall in left field. Being an epistemically astute fellow, it occurs to you that the reason these people are standing and cheering is because they believe what you believe: that Pujols just hit a home run. Furthermore, their beliefs are independent in that each belief is based on the person's seeing the ball land in the bleachers (this is a bit an idealization but not one that is harmful). What we have here, then, is 45,000 pieces of independent testimony. But what is your primary reason for the belief that Pujols homered? Surely it is that you saw it. Yes, you get corroboration from the reaction of the other fans but the main epistemic significance of that is to give you a defense against someone who charges that you didn't see what you thought you saw. One objection to the way I've framed this case is this: yes, you don't get a whole lot of extra support from the 45,000 pieces of testimony but that's just because your evidence was already so strong. In seeing the home run in good conditions, your belief has just about as much evidential support as a belief can have. That you've learned that 45,000 peers agree with you is very significant evidence that by itself would have given you at least as good evidence as you received from perception. That is, had you been looking at your program when the ball was hit and failed to pick up the ball after hearing the crack of the bat, your evidence would still be overwhelming. In fact, if you were then to see a replay on the Jumbotron, your having perceived the home run wouldn't do much to further the epistemic status of your belief. As with the first case, it perhaps bumps it up a little, but the initial evidence was so 19 overwhelming that there was little space between where it took you and the evidential ceiling. The original case is tempting only because perception was temporally prior to testimony. But when you swap the order, you get exactly parallel results. This isn't a case, then, in which psychological evidence fails to swamp because it is not as robust as perceptual evidence but only because it arrives on the scene only after an already-overwhelming evidential case is had.12 I agree with most of what's said in this paragraph: i.e., if you had not seen the home run, you'd still have overwhelming good reason to believe that it happened. After all, simultaneous testimony of 45,000 people to an event that was not particularly improbable in the first place puts one in an awfully good epistemic position. But the above point was not that testimony is epistemically impotent but only that a single clear and distinct perception is extremely evidentially weighty (I'll have more to say about this presently). Even in this second case in which you are reading your program during Pujols' at bat, after see the replay you'll take that to be your primary evidence of the home run. But the reverse doesn't happen in the former case (and this is reason to think that Kelly has at least drastically overstated the swamping point): you'd never cite as your reason for your belief that 45,000 fans stood up and cheered. That only becomes relevant if you face a skeptical challenge: if you are asked "how can you be sure it was a home run and not just a long fly ball?" you can reasonably respond by saying that long fly balls don't receive standing ovations. My point in discussing the Pujols case is threefold. First, while testimony is a good source of evidence, it pales in comparison with clear and distinct perception. Second, there are certain kinds of first-order (i.e., "non-psychological") evidence that are immune to the second-order ("psychological") swamping that Kelly discusses. The third, related point is that clear and distinct perception is one type of evidence that is positively unswampable. What I mean is that it is unswampable in a positive direction. Perhaps if 45,000 people with independently arrived at beliefs tell me that I'm wrong, I am 12 Tom Kelly made this response along these lines in an email exchange. 20 unreasonable should I hold on even to what seems clear and distinct. But their telling me I'm right doesn't become my salient piece of evidence for a clear and distinct perceptual belief. Section V: The Evidential Import of Perception, Part II In the last section, I claimed that perception is positively unswampable. Why should that be? In this section, I'll attempt to answer that question with some help from the writings of the first great evidentialist, John Locke. Locke, it seems to me, is an underappreciated epistemologist. When a philosopher talks about Locke's epistemology, she's liable to speak of the tabula rosa, representative realism and its troubling veil of perception, his difficulty accounting for abstract ideas, and his wholly unconvincing response to skepticism. None of these inspire great confidence in his epistemology; I grant all of that. But I think he had a very deep insight into knowledge. In this section, we'll have a quick look at what Locke has to say on this score. My goal will be to glean an account of why perceptual evidence is so evidentially robust. According to a well known passage at the beginning of Book IV of An Essay Concerning Human Understanding, knowledge is ...nothing but the perception of the connexion of and agreement, or disagreement and repugnancy of any of our ideas. In this alone it consists. Where this perception is, there is knowledge, and where it is not, there though we may fancy, guess or believe, yet we always come short of knowledge.13 We won't tarry long here except to point out this: on Locke's view what distinguishes knowledge from belief is that the former but not the latter is a perception of agreement or disagreement among ideas. Now of course the perception of which Locke writes here is not sense perception. But he nevertheless takes it that we have the ability to perceive the ideas in our minds and in many instances the 13 Locke 1959 pp. 167-8. 21 relationships among them. The most direct and secure form of knowledge Locke dubs "intuitive." When I reflect, I know that the proposition "A triangle has three angles" is true because I can perceive the agreement of ideas; I know that "All uncolored objects are red" is false because I can perceive the disagreement of ideas. The second best grade of knowledge on Locke's view is "demonstrative" wherein pieces of intuitive knowledge are strung together. Locke writes, [W]here the agreement and disagreement is by this means is plainly and clearly perceived, it is called demonstration; and it being shown to the understanding, the mind is made to see that it is so.14 According to Locke, the final and by far weakest variety of knowledge is sensitive knowledge. Lacking the certainty that the other types of knowledge provide, sensitive knowledge is derived from sense perception: when I see the book on the desk, I know that the book is on the desk. According to Locke, the only knowledge we have of the external world is sensitive knowledge; and we only have sensitive knowledge of what we perceive when we perceive it. The minute I look away from the desk and stop seeing the book, I lose knowledge and now have mere (if very well justified) belief. So on Locke's view, what is essential to every form of knowledge is perception. One knows that P only if one perceives that P (for some broad understanding of "perceives"). But, one might wonder, why should perception be held up as the ultimate amongst the various ways of rationally acquiring beliefs? After all, doxastic states are also the result of perception, memory, testimony, induction, deduction, and non-perceptual rational intuition. Why is perception so special? Notice, too, that the answer is not that perception is infallible. Had Locke stuck only with intuitive and demonstrative knowledge, he might have been able to make that claim. But since he takes sense perception to be a source of genuine knowledge (as opposed to mere probable belief), he gives up 14 Locke 1959, p. 179 22 on the idea that only that which is infallibly known is known at all. So if it isn't that perception guarantees truth, and if there is no argument that all cases of perception are in principle more likely to be true than are instances of judgment grounded in other faculties, why is perception privileged? There is, it turns out, a good answer to this question. However, while I strongly suspect that this answer is behind Locke's willingness to credit sensitive knowledge as a legitimate type of knowledge, it is not an answer that is compatible with his stated epistemology. In the broadest sense of the term, to perceive that X is F is to be immediately aware that X is F. This immediate awareness includes but is not limited to sensory perception. So, as we've seen, what we typically call "rational intuition" is a form of perception when it is clear and distinct: when I aim my mental gaze on the proposition that nothing is both F and not-F in the same way at the same time, I perceive that it is true. So perception includes certain cases of rational intuition (and the obvious deductions of propositions known by rational deduction). Naturally, sense perception also falls under the category of perception. But not all sense perception is clear and distinct. And the sort of perception that I am claiming provides maximal evidential support is only the clear and distinct sort. So, for example, if I am hiking at dusk and I get a brief glance of an animal in the distance, I don't have a clear and distinct perception and so my belief that I saw a deer (as opposed to an elk, say), while perhaps having some evidential support, is not particularly well justified. So the variety of perception upon which I'm focusing includes but is not limited to sense perception; and it does not include all instances of the latter. What's so special about perception so characterized? One might be tempted to think that it is the immediacy of the knowledge. The fact that there is no intermediate perceptual object means that the contact had with the object in question is direct; and epistemic directness is evidentially superior to epistemic indirectness. 23 While I think there is something to this, and that other things being equal immediacy is to be preferred to mediacy, the evidential punch packed by clear and distinct perception is not to be explained by directness. For consider the earlier case of the person who, in good light, is capable of reliably distinguishing deer from elk, and yet whose abilities diminish drastically with the fading light. If the direct realist account of perception is right, the object that the person is in direct epistemic content with just is the animal in question even when she sees it at dusk. So her seeing the animal then will count as direct perception but it clearly lacks the evidential force of clear and distinct perception. So the fact that clear and distinct perception is epistemically direct does not account for robust probative power of clear and distinct perception. Enough holding out: what I take to be the key feature of clear and distinct perception in virtue of which it is the cream of the evidential crop is its presentational nature. That is to say, when one clearly and distinctly perceives that X is F, X is F is present to one's consciousness. One knows that it is true not because of an inference to the best explanation or because it is the result of a long and complicated deductive or inductive inference or because one has read it in a book or heard it from a friend or because one recalls it or because it seems to one to be true, but because one has experienced in the most immediate way humans are capable of experiencing the F-ness of X. This presentational aspect of perception, while difficult to state with the kind of precision in which analytic philosophers take comfort, is nevertheless common in each case of clear and distinct perception regardless of mode. 15 Clear and distinct perception is such great evidence because the content of the belief is presented to one's consciousness. 15 Keep in mind that as I am using the phrase "clear and distinct perception" not all perception fits the bill . I'm inclined to think that there are possible modes of perception that involve no presentational aspect at all. That is, perception might reasonably be thought to be (something like) the direct acquisition of knowledge of one's immediate environment, and in principle a zombie could have literal perceptual processes so defined. See Lyons 2009 for an account of perception that takes the presentational component to be unnecessary. What the zombie would lack, however, is "clear and distinct perception" since that requires presentation to consciousness. 24 While no one seriously doubts that clear and distinct perception is extremely reliable, it should be noted that as I'm here using the expression, the success aspect of perception is not assumed. That is, inhabitants of a demon world will have the same clear and distinct perceptual experience that we have when, e.g., we see nearby medium-sized physical objects in good light. Demon-worlders will have unreliable clear and distinct perceptions and these experiences will provide them with evidence that is, at least internally construed, every bit as good as the evidence that those of us in non-demon worlds have.16 As I said earlier, while this idea that the best evidence comes when the fact that X is F is perceptually presented to one is clearly an important part of Locke's epistemology, he can't tie the evidential heft of perception to its presentational nature-or at least he can't without making a significant change to his account of sense perception. For while he thinks we have genuine perceptual knowledge (as opposed to mere opinion or judgment) of physical objects, these objects are never themselves present to our consciousness; it is only our perceptual ideas that we experience. This (and not the fallibility of sense perception) is why Locke's counting sensitive knowledge as genuine knowledge is often felt to be a cheat given Locke's theory of knowledge. On Locke's view, one knows what is perceptually present to one's consciousness and physical (or as Locke would say "sensible") objects never are. If Locke is to stand by his presentational account of knowledge, then he should either deny that we ever have perceptual knowledge (rather than opinion or judgment) of physical objects or give up his representationalism and allow that we perceive these objects directly and hence that they themselves are present to our consciousness. 16 Although I'll grant that clear and distinct perception is strong evidence even at demon worlds, I am not thereby committed to thinking that perceptual beliefs at demon worlds are justified in the sense that is relevant to knowledge. See Senor 2010 for an argument that no empirical beliefs are justified at demon worlds. Notice, too, that even though, construed internally, clear and distinct perception is as good evidence at a demon world as it is at non-demon worlds, perceptual evidence at demon worlds is nevertheless systematically misleading. This strongly suggests that, contrary to what is claimed by many evidentialists, evidential relations have important contingent, external features. 25 Let's take stock. In the previous two sections, I have been arguing that clear and distinct perception is the best kind of evidence we can get, not only because of its reliability but also because the object of our belief is presented to us-we see that it is true. Other modes of belief acquisition lack this presentational feature: the difference here is akin to that between seeing something for yourself and being told that something is the case. Our attention has been focused on clear and distinct perception, but we shouldn't think that anything less is evidentially insignificant. That is, while clear and distinct perception is the evidential top-of-the-line, other, lesser grades of perception are still highly evidentially salient. So if I get a reasonably good look at a person from something of a distance and come to believe that it is my friend Ted, I'll be prima facie reasonable in believing that it is Ted. If you are with me and you're as familiar with Ted as I am, and you tell me that you don't think it was him (or even that you don't have a belief one way or the other) then my reasonability will be somewhat diminished but I'll still have good perceptual evidence that P and a testimonial defeater, and it might well be that the overall strength of my evidence still supports my belief that I saw Ted. Assuming that what I've been saying about the evidential heft of perception is on the right path, what is the upshot for the issue of rational disagreement? It is at least this: where the evidence in a dispute is at least partially perceptual, there is a strong possibility that the weight of the evidence will pull in different directions even after disclosure (since when I disclose my reasons I present testimonial evidence rather than the perceptual evidence that will often be my most salient evidence). This will hold not only for cases involving sense perception but also for rational intuition. Yet this result, although at odds with what many hold in these debates, might seem relatively insignificant since the most important disputes, the ones that really matter to us, don't involve so-called clear and distinct perception or even anything much like perception at all. Disagreements in politics, philosophy, and 26 religion are much more complicated and not as tied to perceptual experience. So what should we say about these matters? In the next section of this paper, I'll lay out a reason to think that there is reasonable disagreement after full disclosure in all of these domains. But let me first note that religious disagreement often does have a perceptual component. While the claim that there is clear and distinct religious perception is not plausible, that there is typically an experiential aspect to the devout life is beyond doubt. And that there can be apparently perceptual (or perceptual-like) religious experience would seem to be beyond dispute as well.17 So there is reason for separating religious disputes (or at least some of them) from political and philosophical disagreements which have no significant perceptual (or perceptual-like) components. The fact that there is an experiential or quasi-perceptual aspect of religious conviction is relevant in two ways. First, as I've been arguing, perceptual experience provides strong evidence and if there is perceptual religious experience, then the evidential situation of the faithful might be considerably better than that of those who believe in compatibilism or presentism. And, second, as we've noted, perceptual evidence is not transferable-at least as perceptual evidence. You can testify to your experience but you can't give your experience to your peer. So the more a conflict involves perceptual or experiential evidence, the more likely it is that disputants will not share the same relevant pool of evidence. Section VI: Uniqueness and Philosophical Disputes At the beginning of this paper, I claimed that although we might seem to observe reasonable disagreement, there is a strong argument to be made that begins with an epistemic principle and concludes that such disagreement is not possible. In this section of the paper, I will argue that the principle that does a great deal of work for those who deny the possibility of reasonable disagreement is 17 See Alston 1991 for an extended argument for the perceptual nature of religious experience. 27 pretty clearly false, and that once one sees why this is, the principled objection to reasonable disagreements is disarmed. The argument sketched earlier begins with the claim that no body of evidence can support a proposition and its negation. I will now need to be a little clearer on just what this claim is. Introduced into this discussion by Richard Feldman, "The Uniqueness Thesis" (UT) is the following claim: [A] body of evidence justifies at most one proposition out of a competing set of propositions (e.g., one theory out of a bunch of exclusive alternatives) and that it justifies at most one attitude toward any particular proposition.18 Citing Feldman as his inspiration, Roger White puts the UT like this: Given one's total evidence, there is a unique rational doxastic attitude that one can take to any proposition.19 If the UT is right, then there can be no rational disagreement even prior to disclosure. For any particular body of evidence will make only a single doxastic attitude (or credence level) rational and so if two people have the same body of evidence and yet take different doxastic attitudes toward a given proposition, then at least one of their beliefs is not rational. Moreover, if we assume UT and disagreement between peers who share the same evidence is discovered, it is plausible that both should suspend judgment since each should know that at most one of them is responding correctly to the evidence and neither has independent evidence that it is she that is so responding. The result would be that even if one of them were responding correctly to the evidence in the first place and so was rational prior to disagreement, after the dispute comes to light, she now has higher-order evidence that the relation that she took to hold between her earlier evidence and the proposition in question doesn't hold after all. 18 Feldman 2007, p. 205. 19 White 2005, p. 445 28 Given the importance of UT in the argument against rational disagreement, we have good reason to give it careful consideration. What reason do we have for thinking that it is true? In the previously cited paper, White provides the following argument for UT. He is considering a criminal case with a jury deliberating on Smith's guilt. White writes: But the evidence cannot support both Smith's innocence and his guilt. Whatever is evidence for P is evidence for the falsity of not-P and hence is evidence against not-P. Of course, certain elements of or aspects of the total body of evidence might suggest that Smith is guilty, while others suggest the opposite. But it is incoherent to suppose that a whole body of evidence could count both for and against a hypothesis. So then it is impossible that my examination of the evidence makes it rational for me to believe that Smith is guilty but also rational to believe instead that he is innocent.20 The key point here is that evidence for P is by its nature evidence against not-P. So whatever part of the overall evidence set supports Smith's guilt equally supports the claim that it is not that case that Smith is not guilty. So suppose there is a subset of the evidence that, were that all the evidence there were, would make it likely that Smith is guilty; suppose that there is another subset that, were that all the evidence there were, would make it likely that Smith is not guilty. Assuming that these subsets equally well support the proposition they support, then the total evidence set supports neither Smith's guilt nor innocence, since there are equally weighty cases for and against both possible outcomes. White's argument that one evidence set can't support both P and not-P is compelling. However, White draws from this the inference that no evidence set could make rational competing propositions. Yet this inference goes through only if what it is rational to believe is strictly a function of what the evidence supports. But we will now see that there is very good reason to deny this. 20 White 2005, p. 447. 29 There are two independent theses that might be thought to have an equal claim to being called "uniqueness" and that get conflated by White in the just-quoted passage. The first, call it "Evidential Uniqueness" is as follows: EU: For any proposition P and evidence set E, there is a unique, specific, and objective fact of the matter regarding the degree to which E evidentially supports P. It is EU that receives support from White's argument that evidence for P is necessarily evidence against not-P. The second uniqueness principle at work in White's argument can be called "Rationality Uniqueness." According to this principle, RU: For any proposition P and evidence set E, E makes rational a unique doxastic attitude (or credence level) regarding P. Putting these two theses together, we get the claim that rationality of a belief in a given proposition is a precise function of the degree of evidential support one's evidence set provides for it and that for any given amount of evidential support the set provides there is a unique attitude or credence level that is made rational for that proposition. While I've already claimed that EU is plausible, I cannot say the same for RU. If evidence sets were small and evidential relationships transparent, then RU might be right. But for a great many of our beliefs, our evidence sets are large, their contents often hard to determine on reflection, and the relevant evidential relations opaque. This is particularly true regarding our philosophical, political, and religious beliefs. If RU is true, then either we are surprisingly good at detecting evidential relations and calibrating our doxastic states accordingly or we have very few rational beliefs. Yet each of these disjuncts is very implausible. So it seems that while EU might well be true, we have good reason to think that RU is false. 30 Furthermore, consider also that, except in disagreement of the most simple and basic kind, the total evidence relevant to a dispute will far outrace what one is able to call to mind at any given time. So two people may possess all the same evidence, but differ dramatically in the parts of that set that they are conscious of when deliberating on the matter at hand. In such a case, although evidence is shared, it might surely happen that doxastic attitudes will rationally differ depending on what part of the evidence set is recalled. That is, suppose that Graham and Elisa–located on different continents and not communicating with each other-are considering whether the Cubs will play better in the second half of the season than they have played in the first. Let's idealize and suppose that Graham and Elisa have watched the same games, read the same articles, listened to the same prognosticators, etc.; moreover, they've also formed the same beliefs that are relevant to the way the Cubs will perform. As each considers the matter carefully, different pieces of the evidence pool come to mind for each. They sift through what they recall and after giving the matter considerable thought, each comes to a belief- Graham believes the Cubs will do better; Elisa believes they will not improve. Suppose that, in fact, the part of the evidence that Graham has been able to recall, objectively supports the claim that the Cubs will do better (and to just the degree of credence with which Graham holds the belief). On the other hand, Elisa has also reacted exactly appropriately given the evidence of which she been consciously aware. Surely they are both rational in their conflicting beliefs even though their total evidence is precisely the same. But if that is right, then RU is false.21 Given the complexity and opacity of evidential relations, and our inability to hold only a small part of any reasonably large evidence set consciously, we cannot insist that, for every total set of evidence is a unique, specific rational attitude it licenses. Surely, the thing to say is that complex and somewhat opaque relations admit of a range of attitudes. One lesson is that where rationality is concerned, what matters is not so much the objective, precise evidential support that is the subject of 21 Thanks to Jack Lyons for helping me see this point. 31 Evidential Uniqueness, but the degree to which these relations are accessible to the rational mind. A second lesson, however, is that even if we insist that there is a single rational response to a body of evidence, what's relevant is not the total evidence set but only that segment of which is recalled and considered during deliberation. So the same sets of total evidence do not determine a unique doxastic response. Now if they were completely inaccessible such that they would be totally opaque even upon careful reflection by a rational person, then rationality requires suspension of belief about the matter in question. However, there is no reason to believe in complete opacity. Notice too that there is no reason to think that the range of attitudes that is reasonable would be restricted to a minimal range on either the positive or negative side of a single evaluation. That is, it might be that a complex evidence set can make rational a belief that P and yet still make rational a belief that not-P (in someone who doesn't believe that-P of course). That this is plausible has been obscured somewhat by the fact that the disagreement debate has been couched in terms of a conflict of the form "S1 believes that P" and "S2 believes that not-P." But I'm not sure that in philosophical, political, and religious debates the conflict is typically that direct and straightforward. One considers, for example, the various perspectives on the free will debate and comes to believe that libertarianism is right while one's peer is a compatibilist. Now there will be many propositions upon which the libertarian and the compatibilist will disagree but that disagreement is generated by the entailment of what each believes is true: the compatibilist believes that freedom is a matter of having the right causal relationship between one's character, one's decisions, and one's actions whereas the libertarian believes that it is only if actions are not the product of deterministic causal chains that run external to her that she can be free. Now it follows from the compatibilist's perspective that it is false that freedom requires indeterminism; and it will follow from the libertarian's perspective that not all actions that bear the relationships that the compatibilist thinks are sufficient for free action really are sufficient. But the conflict between the compatibilist and the libertarian is not usefully modeled as a "P or not-P" conflict. Or think of a complex 32 criminal investigation in which there are two primary suspects against each of whom a good case can be made. Even if we grant Evidential Uniqueness and acknowledge that the evidence can support at most the guilt of one of them, the complexity of the case might make it very hard to tell what the objective evidential facts are. One detective might well come to believe that the evidence favors one suspect while another detective thinks the second primary suspect is the guilty party. As a consequence of what each takes the evidence to indicate, each will think that the other's perspective is wrong. But neither takes the evidence to directly show the falsity of the other's belief. It is not so much that the dispute has a "P verses not-P" structure but a "P verses R" structure where R entails not-P and P entails not-R. Once you appreciate both the complexity of evidential relations and the structure of disagreement, the fact of peer disagreement becomes much less worrisome. For the problem was supposed to be that when you find that a peer disagrees, you get higher-order evidence to the effect that you haven't judged the first-order evidence appropriately. And if both the Evidential and Rational Uniqueness theses were true, then disagreement would provide significant higher-order evidence that the way you are judging the evidence is incorrect and that your belief is not rational. But once we reject Rational Uniqueness and recognize that where rationality is concerned what matters is what it is rational to take the evidence to indicate rather than what, objectively speaking, the evidence does indicate, we should not be surprised when reasonable people disagree. As long as your belief and your interlocutor's belief are in the allowable rational range, then you've not acquired a reason to think you are irrational in the way you've weighted the evidence since it could well be that both attitudes are made rational by the evidence (even though the evidence uniquely supports only one of them). You recognize before learning of the disagreement that the evidence you possess allows of multiple rational reactions and so finding a peer has who has doxastic state that differs from yours but which falls in the acceptable range doesn't give you a particularly significant reason to reconsider. 33 Before I conclude, I want to reply to an objection to the type of view I'm defending that comes from Roger White. The position I've outlined in this paper is a variety of what White has dubbed "epistemic permissivism." Against permissive theories, White has argued that accepting a belief on the basis of a body of evidence that one thinks could rationally support the belief's contradictory proposition is akin to knowingly taking a pill that randomly will bring about either the belief or its contradictory proposition. White claims: Now I have argued that reflection on my having taken a pill to believe that Smith is guilty should undermine all my conviction on the matter. So likewise, if I have concluded on the basis of the evidence that Smith is guilty, my conviction should be undermined if I really think that a belief in Smith's innocence is also rationally permissible in the light of this evidence. For if I believe this, then I should judge myself no more likely to have arrived at the truth than a random pill-popper. So we have reached the conclusion that I cannot rationally accept the extreme permissivist thesis with respect to one of my own beliefs. That is, believing P is not rationally compatible with believing that one could just as rationally have believed not-P given the same evidence.22 If one assumes that rational agents accept both of the uniqueness theses I distinguished earlier, White is probably right. For together, the uniqueness claims entail that there is a single doxastic state that my evidence makes rational for me. But if I assume that and yet think that I could be rational in holding a different doxastic state given the same body of evidence, then not only do I have incoherent beliefs but I'm apparently committed to thinking that my belief bears no significant relation to my evidence (since if I thought it did, then I'd think any other doxastic state would be irrational); and if my belief bears no significant relation to my evidence and if I think that my evidence is all that the relevant 22 White 2005, p. 450. 34 to the rationality of my belief, then, from my perspective, my belief might as well be produced by a random-belief generating pill. Suppose, however, that Rationality Uniqueness is rejected. And instead I accept something like this: Rationality Pluralism: regarding total evidence set E and proposition P, where E is large and the evidential relations that the members of E bear to P are complex, there is not a single doxastic attitude (or degree of credence) toward P that E makes rational. Notice that Rationality Pluralism is a relatively modest thesis. It doesn't entail, for example, that it is ever possible that an evidence set makes rational both a belief and its contradictory proposition but only that, say, believing and withholding might sometimes be equally rational. Now if I'm a Rationality Pluralist, then I can consistently think that my belief is grounded in and made rational by the evidence and that one who takes a different attitude's belief is also grounded in and made rational by the evidence. There is nothing arbitrary about either of our beliefs given the evidence.23 Conclusion Let's put the pieces of this paper together. The position that emerges from our discussion can be thought of as a version of the Total Evidence View. In cases of disagreement with a peer, as in all cases, rationality requires doing what is allowable given what one's evidence appears to support. My view differs from the positions of others who accept versions of the TEV (e.g., the view of Kelly and the more recent view of Feldman) in two ways. First, the discussion here emphasizes the significance of perceptual evidence in general, and in clear and distinct perception in particular. Generally speaking, perceptual evidence is considerably weightier than testimonial evidence and so the mere fact of disagreement isn't enough to rationally require a 23 See Ballantyne and Coffman, unpublished for other criticisms of White 2005. 35 significant change in one's doxastic attitude inasmuch as it is grounded in clear and distinct perception. So-called "swamping" of strong perceptual evidence occurs rarely. Second, what is relevant for rationality is not the Evidential Uniqueness thesis (which is probably true) but the Rationality Uniqueness thesis (which is almost certainly false). Where rationality is concerned, what matters is what it is reasonable to think the evidence supports and not what the evidence objectively supports. Now of course there will be a great many circumstances when these two go together: I see and hear my son playing the piano on the other side of the living room. My evidence overwhelming supports the proposition that my son is playing the piano; the only state that my evidence rationally supports is a strong conviction that my son is playing the piano. Here, because of the simplicity and clarity of the evidence, the RU and EU deliver the same verdict. But in more complex cases, rationality will prescribe a range of attitudes each of which is allowable to take. I want to conclude by noting that I take the disagreement literature to be primarily about rationality and not about epistemic justification. As I understand it, "epistemic justification" is a theoretical term that picks out the property that, along with truth, was had by the subjects in the original Gettier examples. That is, it is the positive epistemic component of knowledge.24 Rationality, on the other hand, is less clearly defined. For the sake of discussion (and because it is a plausible view), I've here assumed that one important notion of rationality is to be understood along evidentialist lines. However, I suspect that there are other concepts of rationality and the disagreement discussion to date has been silent with respect to them. Be that as it may, my primary contention in this concluding note is that acknowledging the 24 See my paper "Why There is No Justified Belief at Demon Worlds" (unpublished). 36 epistemic importance of an evidentialist conception of rationality does not commit one to accepting evidentialism regarding epistemic justification.25 Bibliography Alston, William P. 1991, Perceiving God, Ithaca: Cornell University Press. Alston, William P. 1993, The Reliability of Sense Perception, Ithaca: Cornell University Press. Ballantyne, Nathan & Coffman, E.J.. Unpublished. "Uniqueness and Disagreement." Christensen, David. 2007. "Epistemology of Disagreement: The Good News." The Philosophical Review 116: 187-217. Elga, Adam. 2007. "Reflection and Disagreement." Nous 41: 478-502. Feldman, Richard. 2006. "Epistemological Puzzles about Disagreement." Epistemology Futures, ed. S. Hetherington. Oxford: Oxford University Press, 216-236. Feldman, Richard. 2007. "Reasonable Religious Disagreements." Philosophers without Gods, ed. L. Antony. Oxford: Oxford University Press, 194-214. Kelly, Thomas. 2005. "The Epistemic Significance of Disagreement." Oxford Studies in Epistemology, eds. J. Hawthorne & T. Gendler. Oxford: Oxford University Press, 167196. Kelly, Thomas. Forthcoming. "Peer Disagreement and Higher Order Evidence." Disagreement, eds. R. Feldman & T. Warfield. Oxford: Oxford University Press. Kornblith, Hilary. Forthcoming. "Belief in the Face of Controversy" Disagreement, eds. R. Feldman & T. Warfield. Oxford: Oxford University Press. Locke, John. 1959 An Essay Concerning Human Understanding, New York: Dover Press Lyons, Jack C. 2009 Perception and Basic Belief: Zombies, Modules, and the Problem of the External World Senor, Thomas D. Unpublished. "Why There Is No Justified Belief At Demon Worlds." White, Roger. 2005. "Epistemic Permissiveness." Philosophical Perspectives 19: 445-459. In this paper I argue for a version of the Total Evidence view according to which the rational response to disagreement depends upon one's total evidence. I argue that perceptual evidence of a certain kind is significantly weightier than many other types of evidence, including testimonial. Furthermore, what is generally called "The Uniqueness Thesis" is actually a conflation of two distinct principles that I dub "Evidential Uniqueness" and "Rationality Uniqueness." The former principle is likely true but the latter almost certainly false. Seeing why 25 Thanks to ...... 37 the Rationality Uniqueness fails opens the door to seeing how mutual reasonable disagreement is possible even among those who share the same evidence.