Abstract
A common view about Moore’s Proof of an External World is that the argument fails because anyone who had doubts about its conclusion could not use the argument to rationally overcome those doubts. I agree that Moore’s Proof is—in that sense—dialectically ineffective at convincing an opponent or a doubter, but I defend that the argument (even when individuated taking into consideration the purpose of Moore’s arguing and, consequently, the preferred addressee of the Proof) does not fail. The key to my defence is to conceive the Proof as addressed to subjects with a different epistemic condition. To sustain this view I formulate some hypothesis about the common general purpose of arguing and I defend that it can be fulfilled even when the addressee of an argument is not someone who disbelieves or doubts its conclusion.
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Notes
As is usual in the discussion of the topics treated here, I am only considering arguments whose premises and conclusion are asserted, not—for instance—sub-arguments where we derive a contradiction as a step in a more comprehensive reductio.
Here and throughout the article, when I allude to the purpose(s) or function(s) of an argument, I mean the “natural” or “proper” rational purpose(s) of the argument, as a member of a generic class of speech acts (and analogously regarding internal reasoning). I do not include non-rational persuasion and other possibly legitimate but even more “deviant” uses of arguments (such as presenting an argument to a thug with the intention of bewildering her in order to avoid a beating).
Davies (2009) rejects Pryor’s classification of the respect in which Moore’s Proof fails as a merely dialectical trait but not an epistemological one. I think that Davies’ rejection (which I partially endorse) is connected with the issue of how to individuate proofs discussed in this section. The rational argumentative purpose of a proof is an integral part of it. If the proof cannot fulfil its rational purpose, the failure is epistemologically (not just dialectically) relevant and we can legitimately describe the situation by saying that the proof fails. A natural way to accommodate this view is to require that such a purpose be part of the identity conditions of the proof.
The parenthetical clause in my formulation is intended to avoid a criticism by Hazlett (2006) of Jackson’s original definition just mentioned in the main text. (Cf. Pérez Otero 2011, pp. 141–142.) Except for this clause, I want my definition of Jackson-circularity to amount to Jackson’s definition: the irrationality of combining those propositional attitudes should be understood as equivalent to the fact that “anyone sane [rational] who doubted [or disbelieved] the conclusion would have background beliefs relative to which the evidence for the premises would be no evidence”. Regarding the option of expressing this kind of issues in terms of combination of propositional attitudes, I follow Davies. (cf. Davies 2000, p. 412; Davies 2003, p. 45)
Davies also proposes what he considers to be changes in Jackson’s definition of petitio, trying to generalize it in a similar way. However, I think that the supposed modifications proposed were already implicitly contained in Jackson’s original definition.
I reject this common view in my Pérez Otero (2013a). Cf. footnote 12 below.
Coliva (2008, p. 237) mentions this possible reply on Wright’s part. I do not agree with Coliva’s criticism of it. According to her, the reply assumes that Wright’s account is indeed the right one. But there is no illegitimate assumption there, just a problem (for Wright) of explanatory simplicity. As I say in the text, invoking a controversial theory conjoined with the hypothesis that we have (at least) tacit awareness of it to explain an almost universal feeling is less simple that invoking solely a less controversial theory.
Cf. my comments on the third axis of scepticism described in Pérez Otero (2011, pp. 20–30). As regards to the prospects of externalism to address the kind of sceptical paradoxes about warrant that worries Wright (an issue that cannot be covered here), I have defended (different) gradualist proposals that are moderately externalist in Pérez Otero (2001, 2008, 2013b).
They are connected at once with propositional and with doxastic warrant. For Pryor the apparent failure of Moore’s Proof is not directly connected with propositional warrant; it is a dialectical failure related to doxastic warrant.
These concepts and the theses Pryor formulates seems to constitute—so to say—the purely coherentist-internalist part of the relations of warrant, within a general view about warrant that is already internalist.
Opposition to accepting Moore’s Proof as a cogent argument has also been expressed in terms of transmission of warrant. If Moore’s Proof does not fail, then—it is assumed—warrant transmits across the argument, so that (in accordance with the Warrant Transmission Postulate mentioned in Sect. 7) we can gain a first warrant for the conclusion (or to reinforce the warrant we had), just by running the argument. Pryor accepts this consequence; but most authors deem it to be too counterintuitive, or even contrary to standard respectable Bayesianism (cf., for instance, White 2006). The discussion of this problem deserves a separate treatment. I approach it in Pérez Otero (2013a), where I challenge the usual assumption that failure of warrant transmission entails failure of the argument (cf. Sect. 7 above).
My proposal here has some connection (but is not equivalent) to Neta’s idea that for Moore, “his Proof is not intended to give us knowledge that we might already have, but rather to display to us the knowledge that we already have” (Neta 2007).
I suggest an analogous modest interpretation of Putnam’s Proof that we are not brains in a vat in Pérez Otero (2012a); Pérez Otero (2012b), to defend it from an accusation of petitio made by Falvey and Owens (1994, pp. 132, ff.). An important difference is that Putnam’s Proof, besides, cannot be so easily classified as Jackson-circular, or as question begging.
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Acknowledgments
The main ideas in this work have been presented at two invited talks: in a session of the Logos Seminar (Universidad de Barcelona, April 2012), and in the Universidad Complutense de Madrid (May 2012). The debates in a Logos Reading Group about argumentation and epistemic circularity that I coordinated during the course 2010-11 have been fruitful too. I am indebted to the respective audiences and to some other people who have read previous versions of this article and have made helpful suggestions. Thanks particularly to Fernando Broncano-Berrocal, José A. Díez, Luis Fernández Moreno, Marta Jorba, Mireia López, Daniel Quesada, Sven Rosenkranz, Javier Vilanova and an anonymous referee of Synthese. Financial Support: Program CONSOLIDER-INGENIO 2010, “Perspectival Thoughts and Facts” (CSD2009-00056), MICINN (Spanish Government). Project “Knowledge, Reference and Realism” (FFI2011-29560-C02-01), MICINN (Spanish Government). Consolidated and Funded Research Group LOGOS (2009 SGR 1077), DIUE (Catalan Government).
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Otero, M.P. Purposes of reasoning and (a new vindication of) Moore’s proof of an external world. Synthese 190, 4181–4200 (2013). https://doi.org/10.1007/s11229-013-0256-6
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DOI: https://doi.org/10.1007/s11229-013-0256-6