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External world scepticism and self scepticism


A general trend in recent philosophical and empirical work aims to undermine various traditional claims regarding the distinctive nature of self-knowledge. So far, however, this work has not seriously threatened the Cartesian claim that (at least some) self-knowledge is immune to the sort of sceptical problem that seems to afflict our knowledge of the external world. In this paper I carry this trend further by arguing that the Cartesian claim is false. This is done by showing that a familiar sceptical argument that targets my knowledge of the external world can be adapted to target my belief that I exist, along with any of my self-knowledge that I know entails my own existence. Thus, my self-knowledge and my knowledge of the external world are subject to the same sort of sceptical problem.

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  1. For the purposes of this paper, we need not worry about how the advocate of the Cartesian claim should define this class.

  2. Shoemaker (1994).

  3. Williamson (2002).

  4. Nisbett & Wilson (1977) present empirical work suggesting that subjects routinely misidentify the factors that influence their reasoning process. Schwitzgebel (2008) argues that we are very unreliable when it comes to introspecting our own mental states, and it might be thought that when we are very unreliable on a topic we don’t know (much) about it. However, most of his argument does not focus on the paradigmatic cases of self-knowledge with which the Cartesian claim is concerned.

  5. See Boghossian (1989).

  6. See Gertler (2015), Falvey & Owens (1994) and Bar-On (2004).

  7. Descartes Meditations on First Philosophy, Cottingham’s (1986) translation.

  8. This principle may require refinement; see for example Hawthorne (2014). However, this refinement is unlikely to affect the sceptical argument in any significant way.

  9. If I accept that my empirical evidence is compatible with the EWS scenario, I might still attempt to employ inference to the best explanation to show that my sensory evidence gives me reason to think that the EWS scenario is false. For example, I might try to reject the EWS scenario on the grounds that it is an ad hoc explanation of my experiences. However, it is difficult to formulate plausible principles for inference to the best explanation that support this response. See Beebe (2009) for discussion of this strategy.

  10. It is hard to find examples of people who have tried to reject the sceptical argument by arguing that the EWS scenario is logically or conceptually incoherent. Perhaps Descartes’ argument that a necessarily existing God could not allow him to be radically deceived is an example.

  11. On the classic expressivist view sometimes associated with Wittgenstain, the utterance ‘I am in pain’ is akin to the utterance ‘ouch’, in that both express the feeling of pain, and do not express a proposition. On this view, the utterance ‘I am in pain’ is not incompatible with the SS scenario, and it might be thought that one could avoid my argument against the Cartesian claim by being this sort of expressivist. This is not a good strategy for two reasons. First, classical expressivism is widely seen as implausible and has few adherents. Neo-expressivist views of the sort endorsed by Bar-On (2019) are becoming more popular, but on these views ‘I am in pain’ does express a proposition, and thus is threatened by the SS argument. Second, since the classic expressivist view says that ‘I am in pain’ does not express a proposition they are committed to the claim that this expression does not express knowledge, and therefore does not express self-knowledge. Classic expressivism therefore offers no hope of vindicating the Cartesian claim by describing a class of self-knowledge that is immune to scepticism.

  12. More precisely, I do not attend directly to myself; see Peacock (2012).

  13. We noted in fn. 9 that one might try to rule out the EWS scenario by appealing to one’s sensory evidence and inference to the best explanation. There is no reason to think that this strategy is any more likely to succeed in ruling out the SS scenario.

  14. I am happy to assume here that thinkers are selves, although I will suggest that the sceptic need say very little about the nature of the self in §2.

  15. See Tester (2013) for this interpretation of Lichtenberg.

  16. See Collins (1982) and Kalupahana (1987) for the prevailing ‘no-self’ interpretation of Buddhist doctrine.

  17. See Sosa (1999) for this response to external world scepticism.

  18. My thanks to an anonymous referee for encouraging me to address the issues raised in this section

  19. This view is usually associated with Hume (1975). See Campbell (1967) and Pike (2006) for more recent defences.

  20. The challenge here is similar to Russel’s (1995) challenge to explain how I know that the world did not pop into existence in its entirety five minutes ago.

  21. Loar (1997) holds that physicalism is necessarily true, and knowable only by empirical means.

  22. See for example Lewis (1983).

  23. Descartes, in P. J. Olscamp’s (1965) translation, Part iv: VI 32, HRI 101.

  24. Stroud (2011) makes the same point as Williams. Unfortunately, neither Williams nor Stroud explain why the incorrigibility of a claim would render it immune to closure scepticism, so the following explanation of why this might be thought to be so is extrapolation on my part.

  25. See for example O’Brien (1994). There is some discussion of how best to formulate the Self-Reference Rule, but the precise formulation doesn’t matter here.

  26. See for example Kaplan (1989).

  27. See for example Evans (1989) and McDowell (1994).

  28. I am grateful to an anonymous referee for this point.

  29. I am grateful to the same anonymous referee for pushing me to address this point.

  30. See also Beebe (2011) for a similar point regarding sceptical arguments intended to threaten my a priori knowledge.

  31. Without this extra belief I am like Nozick (1981), who rejects Closure, and thus sees no incompatibility between my knowing that I have hands, knowing that if I have hands I am not a handless brain-in-a-vat, and my not knowing that I am not a handless brain-in-a-vat.

  32. Thanks to Bernhard Salow, David Horst, Crispin Wright, Adrian Haddock, Peter Sullivan, and Giada Fratantonio for comments and helpful discussion. I’m grateful to the Arts and Humanities Research Council (Grant No. AH/W008424/1) for funding this research.


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Thorpe, J.R. External world scepticism and self scepticism. Philos Stud 180, 591–607 (2023).

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