Abstract
The Cartesian arguments for external world skepticism are usually considered to be significant for at least two reasons: they seem to present genuine paradoxes and that providing an adequate response to these arguments would reveal something epistemically important about knowledge, justification, and/or our epistemic position to the world. Using only premises and reasoning the skeptic accepts, I will show that the most common Cartesian argument for external world skepticism (i.e. the closure-based skeptical argument) leads to a previously unrecognized self-undermining dilemma: it either leads to a reductio ad absurdum, or to avoid this reductio the skeptic must accept that this argument is epistemically idle—it does not provide any support for external world skepticism. Either way, this Cartesian argument cannot legitimately threaten or even call into question our beliefs about the external world. And thus, either way, this Cartesian argument for external world skepticism is not epistemically significant—it is not a genuine paradox and adequately responding to it need not reveal anything epistemically important.
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Notes
Alternatively, external world skepticism is the view that we are not or cannot be justified in believing much, if anything, about the external world, and the Cartesian arguments appeal to global skeptical hypotheses to show that we are not justified in believing much, if anything, about the external world. While I will not focus on this justification version of external world skepticism or the Cartesian arguments for it, I believe my arguments in this paper—against the Cartesian arguments for not having knowledge of the external world—also apply to and challenge these arguments.
Bourget and Chalmers (2014) found that the vast majority of academic philosophers believe external world skeptics is false and Leiter (2020) found that external world skepticism was voted as the “most preposterous” philosophical thesis (see https://leiterreports.typepad.com/blog/2020/01/preposterous-philosophical-views-the-poll-results.html).
“The most popular way of motivating radical scepticism in the contemporary literature is by appeal to so-called ‘closure-based’ sceptical arguments” (Schonbaumsfeld 2016, p. 7). I believe this sentiment is shared by most epistemologists who write on skepticism (e.g. Comesaña & Klein, 2019; Steup & Neta, 2020).
The dialectical burden to “provide arguments” need not require that anyone put forward or be a proponent of the view that an argument defends. This is important to note because, with the possible exception of Unger (1975), no one is an external world skeptic. The Cartesian arguments allegedly provide excellent support for external world skepticism independently of anyone raising or advocating for them. Thus, the dialectical burden does not have to be met by any particular proponent of a side of this debate (i.e. the skeptic vs. the non-skeptic) but rather only needs to be met by the position or arguments for either side of this debate (i.e. external world skepticism vs. the denial of external world skepticism) (cf. Kelly, 2005). However, for ease of exposition, in this paper I will sometimes refer to the Cartesian skeptic as a convenient way to refer to external world skepticism and the Cartesian arguments for it.
I should note that “the” closure argument is a misnomer since there are many different ways of spelling out the details of this argument (e.g. see Pritchard, 2015). I do not have space to canvas all these formulations here and will only show how my self-undermining dilemma applies to what I take to be the most common way of formulating this argument. But regardless of how this argument is formulated, the following sections should make it clear how my self-undermining dilemma can be applied to any version of this argument.
There is also controversy about whether C2 can be motivated independently of the underdetermination-based skeptical argument. If this is the case then, the closure-based and underdetermination-based skeptical arguments are not independent of one another [e.g. see Brueckner (1994), Cohen (1998), Pritchard (2005a), McCain (2013)]. In this paper, I will assume in the skeptic’s favor that both skeptical arguments are independent of one another [see Prichard (2015, 2018) for a recent defense of this claim].
While Moore (1959) also argues that the dream skeptic’s argument “cuts both ways,” he means something different by this terminology. He argues that a rival non-skeptical argument is just as well motivated as the dream skeptic’s argument. On one interpretation of Moore, this attempts to demonstrate a kind of stalemate with the skeptic. My argument is importantly different since it attempts to show that the skeptic’s argument is self-incriminating and defeating—i.e. it can be turned on itself to epistemically defeat its own conclusion.
One might object that an argument leading to the conclusion ‘the premises of this very argument cannot be known’ is both different and not as serious a defect as an argument leading to the conclusion ‘the premises of this very argument cannot be justified.’ To link these kinds of self-defeat in my definition of ‘epistemic self-undermining arguments’ seems to presuppose something like the following controversial epistemic view of inference: S can use a proposition p as a premise in inferential reasoning only if S knows that p (see Williamson 2000, pp. 184-207; Moon 2013, p. 2728). A similar worry seems to befall linking arguments that lead to ‘the conclusion of this very argument cannot be known vs. cannot be justified.’ To link these kinds of self-defeat seems to presuppose that suspending belief in p is the proper reaction to discovering that one does not know p (cf. Decker 2014, p. 1102). In Step 4 of Sect. 2 (and fn. 21), I argue that my self-undermining dilemma does not make either of these assumptions. Thanks to an anonymous reviewer for raising this concern.
I should note that blocking this objection only requires the claim that: If S knows X then S satisfies the conditions for knowing X. I assume this biconditional because I believe it is true and do not think that taking on this additional commitment will likely be challenged since this is widely accepted claim.
As the case is currently described, it allows for fallible knowledge in-line with many prominent modal accounts of knowledge. For example, if I were an Anti-BIV, my belief that I have hands is sensitive (if I did not have hands, then I would not believe it) and safe (I would believe that I had hands only if I had hands). But, the case can be spelled-out to even allow for certain kinds of infallible knowledge [see Dutant (2007, 2016)] while remaining compatible with the how the world appears to us, e.g. an Evil Demon or BIV Scientist could imbue me with an infallible power to discern whether I am being deceived by an illusion or am experiencing the real world but, from my first person perspective, it appears to me that I am forming my belief based on my sensory and fallible sense perceptions when I am using my infallible power. If this were the case, then I would presumably satisfy the conditions for infallibly knowing that I have hands (e.g. this power makes it that my belief that I have hands cannot be wrong (cf. Dutant, 2007, p. 73) or epistemically unlike any false belief (cf. Dutant, 2016). And given that the closure principle has no restrictions on the kind of hypotheses that can be plugged into it, the skeptic cannot object to this and other anti-skeptical possibilities.
However, as will be shown in next the next section, this objection points to a reductio argument against the closure argument. I argue that if the skeptic’s reasoning also allows me to satisfy the conditions for, and hence, know that I don’t know that I have hands (via the above biconditional), then the skeptic’s own reasoning leads to a contradiction: I both know and don’t know that I don’t know that I have hands.
I would like to thank my anonymous reviewers for pressing me to make the arguments in this section clearer.
I should note that, while this and similar versions of the closure principle are commonly invoked when explicating the skeptic’s closure argument, it is not clear that they really are “single-premise” closure principles. For instance, if we hold that the inferential statements of the form ‘P entails Q’ are propositions, then the closure principle above requires an agent to know two propositions (to know that ‘P’ and know that ‘P entails Q’) in order to deduce another proposition (Q). However, I will grant for the sake argument that the skeptic intends to use a single-premise closure principle and just assume for ease of exposition that inferential statements that instantiate ‘P entails Q’ are not propositions (cf. Luper, 2018).
In case this is not readily apparent, here is the full rendering of this application of the closure principle: If I know that ‘the consequent of C1 is false,’ and I know that ‘the consequent of C1 is false’ entails C3 (I don’t know that I have hands), and I competently deduce C3 from ‘the consequent of C1 is false’, and I believe C3 on the basis of this competent deduction from ‘the consequent of C1 is false,’ then I know, or am in a position to know, that C3.
Furthermore, it is an interesting fact that the skeptic is forced to deny C8 if C6 and C7 are true because together C6 and C7 entail ~ C8. In this and the following section, I defend C8 and the dialectical burden requirement from objections.
Thanks to an anonymous reviewer for raising these objections.
This paper does not assume any specific account of ‘position to know’ but relies on how it is commonly used and understood in English. That said, I am tempted to say that at a minimum a deductive argument puts S in a position to know its conclusion C only if there is at least one world where the argument is not just valid but sound, and if S were to learn of this argument in this world, S could make the appropriate inference(s) in this argument to come to know C. A defense of this claim is outside the scope of this paper. See Yli-Vakkuri and Hawthorne (2022) and reference therein for a discussion of ‘position to know’ and the difficulties in precisifying this notion.
‘In deductive arguments’ is needed to avoid Gettier-style counterexamples, e.g. there is no possible world in which a stopped clock puts you in a position to know the time (even if it is displaying the correct time), but the stopped clock still might provide adequate justification to believe the time it displays. Limiting the scope of this principle avoids such counterexamples since the premises of a deductive argument logically entail their conclusion while Gettier-cases, like the stopped clock case, only provide inductive support for their conclusions. And given that the skeptic’s reasoning concerns the deductive closure argument, this clause does not beg the question against the skeptic.
See Rosenkranz (2018) for a discussion of similar principles that link propositional justification and ‘being in a position to know.’
In response to fn. 9 specifically, this also provides a special case where the self-defeat involved in ‘the premises/conclusion of this very argument cannot be known’ leads to the kind of self-defeat involved in ‘the conclusion of this very argument cannot be justified.’ If a deductive argument is self-undermining in a way that makes it impossible to know its conclusion, then this argument also epistemically self-undermines its own justification for its conclusion. As such, this also shows that my account of epistemic self-defeating arguments does not assume the claims from Williamson, Moon, or Decker. However, I should note that I am not opposed to the claims from Williamson, Moon, or Decker. Indeed, I believe there is some plausibility to these claims. That said, I believe my self-undermining dilemma is a more convincing and powerful response to the closure argument if it does not rely on such controversial claims.
However, in response to this, the Cartesian skeptic could accept some paraconsistent logic like dialethism. This would allow the Cartesian skeptic to coherently accept that her closure argument leads to a contradiction while also denying that this is a problematic result. Indeed, depending on the details, this may even allow the Cartesian skeptic to show that their argument does demonstrate that we lack knowledge of the external world, despite this argument’s reasoning leading to a contradiction. While this is an interesting possibility, I will have to set aside such concerns since they are outside the scope of this paper. However, I should note that I am not aware of anyone who argues that the Cartesian skeptic does or should adopt a paraconsistent logic, let alone dialethism. So, if my self-undermining dilemma leads to the skeptic to adopt an unorthodox logic, then I take this to be a significant result and one that further contributes to the literature on Cartesian skepticism. Thanks to an anonymous reviewer for raising these objections and showing me the need to respond to them.
As Lycan (2019, p. 53, 77) confidently puts it: “on any philosophical topic, the person who propounds an analysis is going to get creamed.”
Rinard and others [e.g. Wright (1991), Wilson (2012), and Lai (2020)] have also attempted to show that the Cartesian skeptic’s argument is self-undermining. While there are many similarities between our different ways of attempting to accomplish this, a full explanation of this is beyond the scope of this paper.
However, I should note that other epistemologists have gestured at something like my self-undermining dilemma but have not found it to be a worthwhile response to the arguments for external world skepticism. For example, Greco (2000, p. 62) writes that “this kind of response is dismissive because it does not engage any particular skeptical argument…and cannot be sustained on even a superficial consideration of actual skeptical arguments.” On the contrary, my dilemma is not dismissive since it engages directly with the reasoning of the closure argument and poses a significant challenge to this prominent skeptical argument.
See Dennett (2009) for a discussion and a nuanced defense of the view that attributing intentional mental states to (many) artifacts is not just instrumentally useful but a theory of attributing real or genuine mental states to artifacts.
This strategy of granting something one believes to be false to gain more insight into a problem has been advantageous in other areas of philosophy too, e.g., Thomson (1971) grants what she takes to be the false assumption that the fetus is a person from the moment of conception to argue that, even if this is true, abortion is still permissible in many cases.
This defense of the dialectical burden might go some way in addressing and responding to a worry posed by Pyrrhonian scepticism—which on some interpretations [see Lammenranta (2008)] would deny the need to meet a dialectical burden since they do not believe in or assent to any epistemological propositions. The worry is that requiring a dialectical burden might illegitimately rule-out this (and other) more ambitious kind(s) of skepticism. While I believe that Pyrrhonianism is implausible, this is outside the scope of this paper. Instead, I focus only on Cartesian skepticism since it is commonly thought that this latter kind of skeptic aims to put us in a position to know its skepticism [see Comesaña and Klein (2019)]. However, if appealing to Pyrrhonian skepticism is the only way for the Cartesian skeptic’s closure argument to avoid my dilemma, then this, I claim, is still a significant result.
I would like to thank the audiences at the following conferences for providing helpful feedback on this paper: 2022 North Carolina Philosophical Society and the South Carolina Society for Philosophy Joint Conference, the 2021 Wake Forest University Philosophy Colloquium Series, and the 2021 Varieties of Anti-Skepticism (LVI Reuniones Filosóficas) Conference. I would also like to thank Plínio Smith and Michael Williams for their insightful commentaries for the 2021 Pacific APA. A special thanks to my two anonymous reviewers whose comments made this paper significantly better than it otherwise would have been. Thanks to Hilary Kornblith for encouraging this project and discussing skepticism with me over the years. Lastly, thanks to Elizabeth Hupfer for reading and discussing several different versions of this paper and for making this project possible.
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Dixon, J. The insignificance of philosophical skepticism. Synthese 200, 485 (2022). https://doi.org/10.1007/s11229-022-03957-8
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DOI: https://doi.org/10.1007/s11229-022-03957-8