Online research in philosophy

Few philosophers believe that G. E. Moore’s notorious proof of an external world can give us justification to believe that skepticism about perceptual beliefs is false. The most prominent explanation of what is wrong with Moore’s proof—as well as some structurally similar anti-skeptical arguments—centers on conservatism: roughly, the view that someone can acquire a justified belief that p on the basis of E only if he has p-independent justification to believe that all of the skeptical hypotheses that undermine the support lent by E to p are false. In this paper I argue that conservatism does not make trouble for Moore’s proof. I do this by setting up a dilemma concerning the notion of “justification to believe” that figures in conservatism. On one understanding of justification to believe, conservatism is subject to obvious counterexamples. On another understanding of justification to believe, conservatism is consistent with Moore’s “proof” conferring justification upon its conclusion. Since these two understandings exhaust the logical space, the conservative indictment of Mooreanism fails.

In the recent literature on Moore's Proof of an external world, it has emerged that different diagnoses of the argument's failure are prima facie defensible. As a result, there is a sense that the appropriateness of the different verdicts on it may depend on variation in the kinds of context in which the argument is taken to be a move, with different characteristic aims. In this spirit, Martin Davies has recently explored the use of the argument within two different epistemic projects called respectively 'deciding what to believe' and 'settling the question'. Depending on which project is in hand, according to Davies, the diagnoses of its failure—if indeed it fails—will differ. I believe that, by introducing the idea that the effectiveness of a valid argument may be epistemic project-relative, Davies has pointed the way to an important reorientation of the debates about Moore's Proof. But I wish to take issue with much of the detail of his proposals. I argue that Davies's characterization of his two projects is misleading (§1), and his account of their distinction defective (§2). I then canvass some suggestions about how it may be improved upon and about how further relevant kinds of epistemic projects in which Moore's argument may be taken to be a move can be characterized, bringing out how each of these projects impinges differently on the issue of the Proof's failure and of its diagnosis (§§3 and 4). In conclusion (§5) I offer an overview of the resulting terrain.

Moore's 'Proof of an External World' has evoked a variety of responses from philosophers, including bafflement, indignation and sympathetic reconstruction. I argue that Moore should be understood as following Thomas Reid on a variety of points, both epistemological and methodological. Moreover, Moore and Reid are exactly right on all of these points. Hence what I present is a defence of Moore's 'Proof', as well as an interpretation. Finally, I argue that the Reid-Moore position is useful for resolving an issue that has recently received attention in epistemology, namely, how is it that one knows that one is not a brain in a vat?

Abstract: Some seventy years ago, G. E. Moore invoked his own sensory experience (as of a hand before him in the right circumstances), added some philosophical analysis about externality, and took himself to have offered his "Proof" of the existence of an external world. Current neo-Mooreans either reject completely the standard negative assessment of the Proof or qualify it substantially. For Sosa, the Proof can be persuasive, but only when read literally as offering reasons for the conclusion that there is at least one external object—rather than that the prover is justified in believing, or even knowing, that there is at least one external object. Sosa, then, is a neo-Moorean—though not of the sort we might expect in light of the ongoing debate about the Proof. I argue that Sosa needs to say more about the circularity often thought to vitiate the Proof before we can accept his view.

In the contemporary expanding literature on transmission failure and its connections with issues such as the Closure principle, the nature of perceptual warrant, Moore’s proof of an external world and the effectiveness of Humean scepticism, it has often been assumed that there is just one kind of it: the one made familiar by the writings of Crispin Wright and Martin Davies. Although it might be thought that one kind of failure is more than enough, Davies has recently challenged this view: apparently, there are more ways in heaven and earth that warrant can fail to transmit across valid inference from one (set of) belief(s) to another, than have been dreamt of in philosophy so far. More specifically, Davies thinks that a second kind of transmission failure has to be countenanced. He connects each kind of failure of transmission of warrant with two different kinds of epistemic project, respectively, and with the exploration of whether the current dispute between conservatives such as Wright, and liberals such as Jim Pryor, on the nature of perceptual warrant, would have a bearing on them. I point out why Davies’s second kind of transmission failure is indeed no such thing. I then move on to canvass another kind of transmission failure, different from the one studied by both Wright and Davies, and dependent on an alternative conception of the structure of empirical warrants, which I dub “moderatism”. I then consider how this alternative notion of transmission failure fares with respect to Moore’s proof, its relationship with Wright’s kind of transmission failure and with the Closure principle. In closing, I defend it from criticisms that can be elicited from Pryor’s recent work.

Moore’s proof consists of the inference of both “Two hands exist at this moment” and “At least two external objects exist at this moment” from the premise “Here is one hand and here is another.” The paper claims that the proof succeeds in refuting both idealism (“There are no external objects”) and skepticism (“Nobody knows that there are external objects”). The paper defends Moore’s proof against the following objections: Idealism does not deny that there is an external world so Moore’s proof is beside the point; Moore may be mistaken about the premise; Moore has failed to prove the premise; Moore has failed to show how he knows the premise; the proof leads to an infinite regress; the proof begs the question because the premise assumes what needs to be proved; the premise depends upon a shaky inference; the premise rests upon evidence of the senses and thus begs the question; the proof fails to convince the skeptic.

In the last few years there has been a resurgence of interest in Moore’s Proof of the existence of an external world, which is now often rendered as follows:1 (I) Here’s a hand (II) If there is a hand here, there is an external world Therefore (III) There is an external world The contemporary debate has been mostly triggered by Crispin Wright’s influential—conservative —“Facts and certainty” and further fostered by Jim Pryor’s recent—liberal—“What’s wrong with Moore’s argument?”.2 This debate is worth surveying with care because—so I shall contend—it will help us see that, in fact, it allows for an important view that, so far, hasn’t been explicitly considered. The critical survey will be the task of the next two sections, while, in the remaining..

G.E. Moore thought that he could prove the existence of external things as follows: ‘Here is one hand, and here is another, therefore there are external things.’ Many readers of this proof find it obviously unsatisfactory, but Moore’s Proof has recently been defended by Martin Davies and James Pryor. According to Davies and Pryor, Moore’s Proof is capable of transmitting warrant from its premises to its conclusion, even though it is not capable of rationally overcoming doubts about its conclusion. In this paper, I argue that Davies and Pryor have it exactly backwards: Moore’s Proof is not capable of transmitting warrant from its premises to its conclusion, even though it is capable of rationally overcoming doubts about its conclusion.

Moore’s proof of an external world is a piece of reasoning whose premises, in context, are true and warranted and whose conclusion is perfectly acceptable, and yet immediately seems flawed. I argue that neither Wright’s nor Pryor’s readings of the proof can explain this paradox. Rather, one must take the proof as responding to a sceptical challenge to our right to claim to have warrant for our ordinary empirical beliefs, either for any particular empirical belief we might have, or for belief in the existence of an external world itself. I show how Wright’s and Pryor’s positions are of interest when taken in connection with Humean scepticism, but that it is only linking it with Cartesian scepticism which can explain why the proof strikes us as an obvious failure.

According to Wright, Moore’s contentious “proof of the existence of a material world” in not cogent because no warrant can transmit from its premise to its conclusion. Since Bayesian confirmation theory probably affords the best account of inductive reasoning we have today, if Wright’s analysis of Moore’s “proof” could be translated in Bayesian language, it would probably be preferable to rival analyses that cannot be reformulated in the same way. Okasha has recently proposed a Bayesian model that apparently vindicates Wright’s analysis on the whole. In this paper I first argue that Okasha’s Bayesian vindication is in different respects flawed and thus unacceptable. I then propose a more suitable Bayesian framework, resting on the so-called Lockean Thesis, which does vindicate Wright’s analysis. My investigation sheds new lights on the logical features proper to the warrant that Wright deems not to transmit across entailment, on the constituents of the logical “mechanism” that according to Wright engenders failure of transmission, and on the fine structure of the rational architecture of perceptual warrant outlined by Wright.