© LOGOS & EPISTEME, III, 4 (2012): 571-577 JUSTIFICATION AND THE UNIQUENESS THESIS Luis ROSA ABSTRACT: In this paper, I offer two counterexamples to the so-called 'Uniqueness Thesis.' As one of these examples rely on the thesis that it is possible for a justified belief to be based on an inconsistent body of evidence, I also offer reasons for this further thesis. On the assumption that doxastic justification entails propositional justification, the counterexamples seem to work. KEYWORDS: uniqueness thesis, evidential permissiveness, rationality, inconsistency, propositional justification, doxastic justification 1. The Uniqueness Thesis Do you think it is reasonable to claim that one can be rational in believing that p on the basis of certain evidence, while one could also be rational in believing that ~p on the basis of the same evidence? Or, maybe, that one can be rational in believing that p on the basis of certain evidence, while one could also suspend judgment about p on the basis of the same evidence? If you think of one of these as real possibilities, then your belief is inconsistent with the so-called 'Uniqueness Thesis': (U) For any proposition p and body of evidence E, E makes rational a unique doxastic attitude towards p. Arguing against (U) would be providing reasons to believe that there is at least one case in which certain evidence makes more than one doxastic attitude justified towards a certain proposition (I use 'rational' and 'justified' interchangeably here). For the sake of simplicity, rather than using the notion of graded belief, I will assume the tripartite typology of doxastic attitudes here: belief, disbelief and suspension of judgment. Now, (U) is a thesis about how our rational doxastic attitudes are constrained by evidence: there is at most one doxastic attitude – belief, disbelief or suspending judgment – that one can take towards p on the basis of evidence E. Consider some evidence E and any proposition p. Now suppose you rationally believe p on the basis of that evidence. Then, according to (U), it is not possible for anyone to rationally suspend judgment about p on the basis of E, as it is not possible for anyone to rationally disbelieve p on the basis of E. Luis Rosa 572 There are two theses about the permissiveness of evidence which are in direct conflict with (U). The first one is the Extreme Permissiveness Thesis (this name is also used by Anthony Brueckner and Alex Bundy1): (EP) There are cases in which a certain body of evidence E makes believing that p rational, but E could also make believing that ~p rational. If you assume that believing ~p entails disbelieving p, then (EP) implies that there are possible cases where one's total evidence E justify believing p, but E could also justify disbelieving p. There is nothing in (EP), though, that says it is possible for one to rationally believe that p and rationally believe that ~p at the same time. That would surely be a step further from (EP). It is reasonable to think that the (EP) defender allows for specific cases in which evidence has such permissiveness – cases in which S rationally believes p but, in a counterfactual situation where things would somehow be different, S would be equally rational in believing ~p. The other thesis conflicting with (U) is the Moderate Permissiveness Thesis: (MP) There are cases in which a certain body of evidence E makes believing that p rational, but E could also make suspending judgment about p rational. The difference between (EP) and (MP) is that the latter does not imply that there are bodies of evidence which rationalize both the belief that p and the belief that ~p. Nevertheless, the possibility adduced in (MP) is also inconsistent with (U), so that the truth of (MP) is sufficient to deny (U). It is also reasonable to think that the (MP) defender allows for specific cases in which evidence has such permissiveness. In the next section I will examine some possible instances of (EP) and (MP). I did not find in the literature related to the Uniqueness Thesis any consideration about inconsistent bodies of evidence yet. That possibility is considered in the next section. 2. Rationality, inconsistency and permissive cases Suppose Michelle has the following beliefs about her friend, George: (1) George is tired, but willing (2) [If George is tired, he will rest or sleep] and [George is not willing, or it is not the case that he will rest or sleep] 1 Anthony Brueckner and Alex Bundy, "On 'Epistemic Permissiveness'," Synthese (2011), DOI: 10.1007/s11229-011-9921-9. Accessed August 25, 2012. Justification and The Uniqueness Thesis 573 Now, assume {(1), (2)} is Michelle's total evidence, and that both (1) and (2) are rationally believed by her. It may be evident to someone reading this paper that the set {(1), (2)} is an inconsistent set – but let us also assume Michelle does not realize that. I take for granted here that, in some cases, we have inconsistent bodies of evidence not identified as such (that is why sometimes we get surprised when a colleague shows some consequences of our assumptions to us!). If you feel uncomfortable saying that {(1), (2)} is a rational set of beliefs, think about the costs of assuming that there is no rational set of beliefs which is also inconsistent. Your belief may be irrational right now, if there is some undetected inconsistency in your total evidence – and sometimes it takes a lot of logical maneuver to discover an inconsistency. More on that below. Without realizing any inconsistency in her body of evidence, Michelle reasons as follows: (3) George is tired (from 1) (4) If George is tired, he will rest or sleep (from 2) (5) George will rest or sleep (from 3, 4) So Michelle believes (5), and I see no reason to claim that her belief in that conclusion is irrational or not justified. Her reasoning is valid, her pre-inferential beliefs are justified and no defeater has come to her mind. Nevertheless, Michelle could have reasoned the following way: (3') George is willing (from 1) (4') George is not willing, or it is not the case that he will rest or sleep (from 2) (5') It is not the case that George will rest or sleep (from 3', 4') In this counterfactual situation, Michelle's reasoning is also valid, her preinferential beliefs are justified and, again, no defeater comes to her mind. If we attribute justification to Michelle's conclusion in the first case, I see no reason to deny it in the last one. Granted, in both cases she could have inferred a contradiction – the conjunction of (5) and (5') –, but what if she does not? Is she irrational in having those beliefs only because she did not make the relevant inference? The conclusion here would be that Michelle rationally believes that George will rest or sleep, but she could also rationally believe that it is not the case that George will rest or sleep – I take that to be an instantiation of (EP). It may not be clear why Michelle's case is an instantiation of (EP). One may want to call attention to the difference between propositional and doxastic justification, and claim that Michelle's case is about doxastic justification, while (U) is a thesis about propositional justification. I address this kind of concern in Luis Rosa 574 the next section, in which I emphasize that every case of doxastic justification is a case of propositional justification. But first let me deal with the observation that I may have been too hasty in granting that one can be rational in believing something on the basis of inconsistent reasons. One may still think that, in the case present case, Michelle cannot be rational in believing (5), because her reasons are inconsistent. The case I want to talk about is a very well-known episode: in the beginning of the twentieth century, Sir Bertrand Russell showed that Frege's logical axioms are inconsistent. The axioms of the logic system envisioned by Frege are shown to be inconsistent by entailing the possibility of the set of all sets that are not members of themselves2 – and that paradoxical consequence was not foreseen by Frege himself. In fact, it took some brilliant deductive ingenuity to infer that paradoxical consequence. Now, does that mean that Russell's doxastic attitudes about Frege's theorems are rational (because he realized that Frege's set of axioms is inconsistent) while Frege's doxastic attitudes about those theorems, previously to the discovery of the paradox, are not (because he did not realize his axioms are inconsistent)? If you are willing to say "Yes, Frege was really irrational, because one cannot be rational in believing something on the basis of inconsistent beliefs, even if the inconsistency was not detected," I would say you may be taking rationality to be logical omniscience – which it is not. Now if you grant that, prior to Russell's discovery, Frege's beliefs in the theorems of his logical system were rational, then you are committed to the possibility of rational beliefs formed on the basis of inconsistent bodies of evidence. Of course, after realizing the paradoxical consequence, Frege must 'do something' to fix his belief-system. In order to be rational, he must suspend judgment about one (or more than one) of his axioms. So, it is not clear that one cannot be rational in believing something on the basis of an inconsistent body of evidence not identified as such. Michelle's case seems to be a case of rational belief. The evidential body {(1), (2)} makes rational more than one doxastic attitude towards the proposition (5). Now let me present a case which is a possible instantiation of (MP). In this example, we also have an actual and a counter-factual situation, but the difference between them is more radical. Suppose Amanda justifiably believes both: (i) If I clicked the wrong link, my e-mail has a virus now. (ii) My email has no virus now. 2 Is it a member of itself? Justification and The Uniqueness Thesis 575 While having those justified beliefs, Amanda also entertains the following hypothesis: that she did not click the wrong link. In world W1, Amanda infers: (iii) I did not click the wrong link. She is working perfectly, from a cognitive point of view, in W1 – she reasons in accordance with the modus tollens inferential rule, and correctly believes (iii) on the basis of (i) and (ii). As she also lacks any defeater to her newly acquired belief, we would say Amanda's belief that (iii) is also justified. In world W2, though, despite having the same evidence and entertaining the same hypothesis, Amanda does not manage to infer (iii), because she lacks the inferential ability to reason in accordance with modus tollens. It is as if she does not have the needed algorithm to generate an output of the form ~p given the inputs of the form p→q and ~q. In this world, Amanda does not have the foggiest idea why she should believe the entertained hypothesis expressed by (iii), so that she suspends judgment about that proposition. Besides, nothing indicates to her that she is wrong in suspending judgment about (iii) – as far as she can tell, she has no good reasons to believe such a thing on the basis of (i) and (ii). Amanda is really unfortunate in W2. But is she irrational in suspending judgment about (iii)? How could we expect her to rationally believe (iii) if she is cognitively constrained in such a way that she cannot reason from (i) and (ii) to (iii)? In this example, Amanda has exactly the same total evidence in worlds W1 and W2. Nevertheless, in W2 she rationally suspends judgment about a proposition in which she rationally believes in W1. Think about labeling Amanda as irrational in W2. What is the rational attitude she must take towards (iii) then? If you say that in order to be rational she must believe (iii), you are implying that it can be rational for S to believe p on the basis of E when S sees no reason to believe that p. I take Amanda's case to be an (MP) instantiation. Let us call the instantiations of (EP) or (MP) 'permissive cases.' 3 Again, it may not be clear that Michelle's and Amanda's examples are permissive cases. These are examples about doxastic justification (in which S justifiably believes that p), while (U), (EP) and (MP) are taken to be theses about propositional justification (in which S has justification to believe that p). I address this observation in the next session. 3 Both Brueckner and Bundy, "On 'Epistemic Permissiveness'," and Roger White, "Epistemic permissiveness," Philosophical Issues 15 (2005): 445-459, use 'permissive cases' to denote (EP) cases. I will use that expression to denote not only (EP) cases, but also (MP) cases. Luis Rosa 576 3. Propositional and doxastic justification Jonathan Matheson,4 a uniqueness defender, emphasizes that (U) concerns propositional justification only. He says the kind of justification relevant to (U) "is solely a relation between a body of evidence, a doxastic attitude, and a proposition."5 So, how cognitive agents have come to gather their beliefs toward a proposition would not be relevant to the uniqueness debate. This is the very same point made by Roger White6 when he says he is interested in the rational constraints evidence alone puts on belief. But this kind of observation may fail to take into account the fact that there is a very tight conceptual relation between propositional and doxastic justification. You cannot truly assert, for example, that Frege justifiably believes theorem T while you also truly assert that Frege does not have justification to believe T. That claim would be inconsistent with the following epistemic principle: (DJ→PJ) If S justifiably believes that p, then S has justification to believe that p This epistemic principle entails, by modus tollens, that if S has no justification to believe that p, then it is not the case that S justifiably believes that p. So in Michelle's case, if we grant that she justifiably believes that (5), we are committed to the thesis that Michele has justification to believe (5). But as she could justifiably believe (5') in a counterfactual situation, we would also have to say she has justification to believe (5'). How could you explain her justifiably believing (5) if you are not willing to grant she has justification to believe this proposition? You could reply: "You are implying Michelle's evidence is the same in both cases – and this is not true, because in the first case she uses (3) and (4), while these propositions are not used by her in the second one." But (U) says that, for any body of evidence and any proposition, there is a unique rational attitude one can take towards that proposition on the basis of that evidence. So, we would expect that there is a unique rational attitude one could take towards (5) on the basis of {(1), (2)}, and the example shows this is not the case. We could conceive a third possibility about Michelle's reasoning – one in which she infers (5) directly from {(1), (2)}. Similarly, we could conceive a fourth possibility – one in which she infers (5') directly from {(1), (2)}. 4 Jonathan Matheson, "The Case for Rational Uniqueness," Logos & Episteme II, 3 (2011): 359373. 5 Matheson, "The Case for Rational Uniqueness," 360. 6 White, "Epistemic permissiveness," 445. Justification and The Uniqueness Thesis 577 In Amanda's case, if we grant she justifiably believes (iii), then we are committed to the thesis that she has justification to believe (iii) in W1. But in W2 she justifiably suspends judgment about (iii). So, she has justification to suspend judgment about (iii) in this case. Given that Amanda's total evidence is the same in both cases, we have an (MP) case. You could reply: "But, in the second case, the one in which Amanda fails to make the relevant inference, her total evidence is different – she may believe (i) and (ii), entertain the hypothesis (iii), but in order to rationally suspend judgment about (iii) she needs to believe something like 'I have no good reason to believe (iii),' and that implies Amanda's evidence in W1 is different from Amanda's evidence in W2." Nevertheless, in W2, Amanda does not need to believe something like "I have no good reason to believe (iii)." She only needs to fail to realize she has good reasons to believe (iii). No second-order thought are needed in order for her to suspend judgment about (iii). It is easier to understand Amanda's example by supposing that in both, W1 and W2, the only things she has as evidence are the beliefs (i) and (ii) and the hypothesis (iii). So far, the argument here is as follows. Let us say that in Michelle's and Amanda's cases we have a permissiveness about doxastic justification: (Permissiveness about doxastic justification) It is possible for S to justifiably form doxastic attitude D1 towards some proposition p on the basis of some evidence E while it is also possible for S to justifiably form doxastic attitude D2 towards p on the basis of E, where D1 ≠ D2. We have no direct reference to propositional justification here. But one need only to put this thesis together with the principle (DJ→PJ) to obtain: (Permissiveness about propositional justification) It is possible for S to have justification for doxastic attitude D1 towards some proposition p on the basis of some evidence E while it is also possible for S to have justification for doxastic attitude D2 towards p on the basis of E, where D1 ≠ D2. So, it seems that permissiveness about doxastic justification requires the truth of permissiveness about propositional justification. If the cases presented instantiate permissiveness about doxastic justification, then they also instantiate permissiveness about propositional justification. That would imply that (U) is false.7 7 I would like to thank Anthony Brueckner and Rodrigo Borges for valuable comments on earlier drafts of this paper.