Abstract
Impurism says that practical factors encroach on knowledge. An important version of impurism is called ‘Threshold-Impurism,’ which says that practical factors encroach on the threshold that rational credence must pass in order for one to have knowledge. A prominent kind of argument for Threshold-Impurism is the so-called ‘principle-based argument,’ which relies on a principle of fallibilism and a knowledge-action principle. This paper offers a new challenge against Threshold-Impurism. I attempt to show that the two principles Threshold-Impurists are committed to—KJ and Fallibilism—are jointly in tension with a widely-held principle of credence that’s called ‘Truth-Directedness,’ in the sense that the former two principles cannot both apply to those who know the third. This tension constitutes a serious challenge to Threshold-Impurists, because it leaves them two options, both of which are undesirable: denying Truth-Directedness, or accepting Truth-Directedness and accepting that whether KJ and Fallibilism apply to a person depends on whether she knows Truth-Directedness.
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Notes
In this paper, I don’t distinguish ‘certainty’ from ‘credence one’—all occurrences of ‘certainty’ in this paper could be replaced with ‘credence one’ without undermining my main arguments.
Thanks to an anonymous reviewer for pressing me to clarify my aim.
Proponents of Threshold-Impurism include Basu (2019), Fantl and McGrath (2002, 2009), Ganson (2008), Grimm (2011), Hannon (2017), and Pace (2011). Proponents of Credence-Impurism include Clarke (2013), Gao (2019) and Greco (2015). (I should note that, strictly speaking, what Clarke, Greco and Gao primarily defend is still a psychological thesis which says that credence is pragmatically encroached on, not the normative thesis. However, some of these authors’ arguments can also be used to support the normative thesis.).
Fantl and McGrath (2009) use the notion ‘epistemic probability’ when they talk about epistemic positions. But it’s reasonable to assume that Threshold-Impurists in the literature use ‘epistemic probability’ and ‘rational credence’ interchangeably. In fact, Fantl and McGrath (2009, pp. 1314) themselves have argued (convincingly in my opinion) that rational credence matches epistemic probability. Of course, knowledge-firsters tend to use a third notion, namely, ‘evidential probability,’ to measure epistemic position, and some of them have claimed that rational credence need not match evidential probability (Williamson, 2000, pp. 21,314). But as I will soon explain, the target of this paper is Threshold-Impurism, and knowledge-first impurists in the literature (such as Hawthorne & Stanley (2008)) are not Threshold-Impurists, since they tend to think that the evidential probability itself, not the threshold, shifts across practical contexts.
Credence-Impurism has been developed in two ways. The first is a knowledge-first style (Hawthorne & Stanley (2008)). Knowledge-first impurists measure epistemic position by ‘evidential probability’ and they think the evidential probability itself shifts across contexts, because they define evidential probability in terms of knowledge and they think that knowledge shifts across contexts. (That said, a knowledge-first impurist would presumably call herself ‘Evidential-Probability-Impurist’ rather than ‘Credence-Impurist’ if he, like Williamson, thinks that evidential probability needs not match rational credence). The second way of developing Credence-Impurism focuses on the shiftiness of the space of possibilities over which your rational credence function is defined. On this view, the same evidence might warrant certainty in a low-stakes situation but doesn’t do so in a high-stakes situation, simply because more possibilities will be included into the space over which your credence function is defined as stakes rise, and your evidence couldn’t rule out newly included possibilities of error (Clarke, 2013; Greco, 2015).
The impurist might resist the application of closure here. This move will be addressed in Sect. 5.2.
ATD is reminiscent of Kripke’s dogmatism puzzle, which says that, if one knows that p, then one knows that all potential evidence against p is misleading and thus one can ignore such evidence (Harman, 1973, p. 148).
Despite the similarity, the two arguments are distinct enough to warrant different treatments, because current solutions to the dogmatism puzzle won’t help the impurist address ATD. For instance, one solution denies the principle that knowing that evidence is misleading allows one to ignore it (Baumann, 2013; Ye, 2016). This looks like a denial of the principle that knowing a proposition allows one to act on it and thus is not acceptable to the impurist. Another solution says that knowledge doesn’t allow ignoring counter-evidence because having the evidence would defeat one’s knowledge (Harman, 1973, pp. 1489). This defeasibility solution will not help the impurist, as I will argue in Sect. 5.2.
The impurist might claim that binary beliefs aim at knowledge rather than truths and thus, similarly, credence aims at knowledge rather than accuracy. And if asked in what sense credence could be knowledge, the impurist might point to the idea of ‘probabilistic knowledge’ that has recently been defended by Moss (2018b).
A full discussion about the aim of credence goes beyond the scope of this paper; here I only give some tentative reasons to doubt the idea that credence aims at probabilistic knowledge rather than accuracy. Even if belief aims at knowledge rather than truth, it’s unclear why credence similarly aims at probabilistic knowledge rather than accuracy, for the following reasons. In the case of binary belief, knowledge cannot be less valuable than truth, since a binary belief that is knowledge is necessarily also a true belief. However, a credence that is probabilistic knowledge is not necessarily also the maximally accurate credence—when p is true but the epistemic probability of p falls short of certainty, an uncertain credence is probabilistic knowledge but is not maximally accurate; so, we don’t get to say “probabilistic knowledge cannot be less valuable than a maximally accurate credence.” Moreover, if you are asked to choose between a credence in p that is probabilistic knowledge and a credence in p that is maximally accurate, it seems that you should choose the latter—after all, when it comes to those p-dependent decisions, the latter enables you to choose the optimal action in all those decisions while the former doesn’t.
For any value x, [the rational credence in p is x] implies [credence x maximizes expected accuracy], given the following two common assumptions in the epistemic utility project. First, the relevant accuracy measure is ‘strictly proper’ (that is, the measure ensures that every probability function maximizes expected accuracy relative to the probability function itself); second, in rational credence-revision, the relevant probability underlying expected accuracy is the rational credence function.
Note that impurists can say that, when you don’t know which option has the best actual outcome, you can choose the option with the best expected outcome even though you know that it doesn’t have the best actual outcome. See Fantl and McGrath’s (2009, pp. 2156) discussion of Parfit’s ‘Mine Shafts’ case.
Weisberg, an advocate of knowledge-action principles, has argued that a reason’s weight can be affected by probabilities (2013, pp. 1318). However, what his argument shows is that a reason R’s weight can be affected by the probabilities of some other propositions, not that it can be affected by the probability of R itself.
Thanks to an anonymous reviewer for suggesting this possible move.
At least these claims are what the abovementioned impurists intend to make. See Worsnip (forthcoming) for an interesting discussion of whether moderate pragmatists can really resist hard pragmatism.
Fantl and McGrath (2009) have criticized two arguments for the claim that KJ doesn’t sit well with Fallibilism; however, their criticisms don’t apply to ATD. First, their criticism to what they call ‘The Argument From Being Certain’ (2009, p. 224) doesn’t apply to ATD, because ATD doesn’t involve the fallacious claim that p is a reason to think that the epistemic probability of p is one (it only involves the claim that p is a reason to think that the most accurate credence in p is one). Moreover, their criticism to what they call ‘The Argument From Hypothetical Gambles’ (Brown, 2008, p. 1144; Fantl & McGrath, 2009, pp. 2256) also doesn’t apply to ATD, because ATD doesn’t involve any high-stakes gambles.
BC* is a rationality-action principle that is implied by Ganson’s (2008, p. 451) BC. It’s also a knowledge-action principle if we assume that knowledge requires rational belief.
The generalization of ATD to BC*-based argument for impurism will be slightly different, because the term ‘knows’ in ATD-KA and in Fallibilism will be replaced with ‘rationally believes.’.
Weatherson (2005, pp. 4223) proposes a similar restriction on his belief-action principle.
An anonymous reviewer has suggested the following response: the impurist can say that, when we ask the question of which credence to have, stakes do become high so that fallible knowledge is defeated—it’s just that the relevant stakes are not practical stakes associated with action, but stakes having only to do with inaccuracy. That is, when we ask which credence in p to have and when the evidential probability of p is below certainty, the stakes that have to do with inaccuracy become high enough so that p is no longer ‘practically adequate.’ (See Anderson and Hawthorne (2019) for the property of practical adequacy.).
This response has the surprising result that, whenever the epistemic probability is below certainty and when we’re facing the question of which credence in p to have, we’ll lack knowledge as to whether p. The reviewer thinks that this result doesn’t lead to skepticism, because the notion ‘facing a question’ should be construed narrowly, so that we don’t often face the question of which credence to have. I’m inclined to disagree. I think that credence deliberation is something we engage in quite often in ordinary life. Perhaps we rarely ask the question explicitly in the form ‘what credence in p should I have?’ but we do often ask the question implicitly by asking ‘how likely is p?’.
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Acknowledgements
For comments and discussion, I’m grateful to Davide Fassio, Jie Gao, audiences at NUS Epistemology Workshop, audiences at Beijing Epistemology Conference, and the anonymous referees of Erkenntnis.
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Ye, R. Knowledge-Action Principles and Threshold-Impurism. Erkenn (2022). https://doi.org/10.1007/s10670-022-00626-7
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DOI: https://doi.org/10.1007/s10670-022-00626-7