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Luck, propositional perception, and the Entailment Thesis


Looking out the window, I see that it’s raining outside. Do I know that it’s raining outside? According to proponents of the Entailment Thesis, I do. If I see that p, I know that p. In general, the Entailment Thesis is the thesis that if S perceives that p, S knows that p. But recently, some philosophers (McDowell, in Smith (ed.) Reading McDowell on mind and world, 2002; Turri, Theoria 76(3):197–206, 2010; Pritchard, Philos Issues (Supplement to Nous) 21:434–455, 2011; Pritchard, Epistemological disjunctivism, 2012) have argued that the Entailment Thesis is false. On their view, we can see p and not know that p. In this paper, I argue that their arguments are unsuccessful.

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  1. Cf. (Unger (1972), pp. 304–305) for this suggestion. But there is a problem for this suggestion. Consider, objectual-perception reports, as in the first conjunct of (1) ‘S sees the bus stopping, but doesn’t know that the bus is stopping’. (1) sounds just as absurd as (2) ‘S sees that the bus is stopping, but doesn’t know that the bus is stopping’. But, plausibly, there is no entailment from ‘S sees an x which is F’ to ‘S knows that x is F’. This result seems to undercut the idea that the Entailment Thesis is what best explains the seeming inconsistency of (2). Dretske (1969) provides a pragmatic explanation for the seeming inconsistency of reports like (1), rather than a semantic explanation (which would appeal to considerations like the Entailment Thesis), and one might think that this kind of explanation can be extended to reports like (2), although it’s not clear that it will work. Thanks to Craig French for pointing this out to me.

  2. Consider two views about visual propositional perception: (WK) ‘seeing that \(p\) is a way of knowing that p’ and (EWK) ‘seeing that \(p\) is a particularly exemplary way of knowing that p’. Notice that it seems possible for (WK) to be true without (EWK) being true. How? First consider this question: what makes a way of knowing that \(p\) a particularly exemplary way of knowing that p? One condition might be that that way of knowing that \(p\) actually implies that the agent knows that \(p\). So, for example, we could explain the truth of (EWK) in terms of the Entailment Thesis, even though the truth of the Entailment Thesis might not explain the truth of (WK). For example, consider (RWK): ‘reading that \(p\) is a way of knowing that p’. Plausibly, we may think that one can read, in a reliable newspaper, say, that a building was just demolished, and thereby come to know that the building was just demolished. But reading that p doesn’t seem to imply knowing that p. After all, we can read that p even if \(p\) is false. I can read that a certain election was rigged even if this isn’t true; perhaps the journalist was mislead, and given false information. Insofar as knowledge is factive, then, it is at least possible for reading that \(p\) to be a way of knowing that \(p\) without entailing that whenever S reads that \(p\), S knows that \(p\). How does this consideration relate to the passage from Cassam? First, we might think that (EWK) provides support for the Entailment Thesis, even if (WK) doesn’t. On this score, I am appealing to the relevant passage from (Cassam (2007a), pp. 343–344) in order to highlight a prima facie motivation for endorsing the Entailment Thesis. But whether this reason can be sustained under scrutiny is open to dispute, and we can see this by looking to some of the other things that Cassam says. For example, it’s not clear that Cassam would endorse the prima facie motivation that I presented in the main body of the text. Here’s why: according to Cassam, \(\upphi \)-ing that \(p\) can be a way of knowing that \(p\) even if ‘S \(\upphi \)-ed that \(p\)’ doesn’t entail ‘S knows that \(p\)’. Of course, Cassam could maintain that for \(\upphi \)-ing that \(p\) to be an exemplary way of knowing that \(p\) it must entail knowledge. But it is not obvious that Cassam does think this. See his (2007a, pp. 345–347) for some discussion on this issue. Moreover, Cassam also seems to hold that explanations of how someone knows that \(p\) in terms of objectual perception (e.g., seeing an object \(o\) which is \(F\); seeing a red tomato) can, in certain sorts of cases, be exemplary explanations of how someone knows that \(p\) in at least something like the way in which explanations of how someone knows that \(p\) in terms of seeing that \(p\) are exemplary. See (Cassam (2008), pp. 39–41) in particular. So Cassam does not appear to maintain that just because certain explanations of how someone knows that \(p\) might be particularly exemplary, such as explanations in terms of propositional perception or objectual perception, the exemplariness of the explanation needs to be explained by appeal to the Entailment Thesis. Furthermore, if it is true that explanations of how someone knows that \(p\) in terms of objectual perception can be exemplary explanations, one might then want to reassess the motivating consideration I highlighted in the main body of the text. After all, if they can be exemplary without being knowledge-entailing, this will be a problem for appealing to the exemplariness of explanations of how someone knows that \(p\) in terms of propositional perception being grounded in the Entailment Thesis. This all requires further discussion, but for my purposes I can set it aside, since I only want to highlight some prima facie considerations which motivate the Entailment Thesis. I have used (Cassam 2007a, 2008) to serve that purpose. But how one ought to read Cassam’s own commitments, and whether those motivating considerations provide adequate support for the Entailment Thesis, are further matters. For theoretical considerations in favor of the Entailment Thesis, see Cassam (2007b), Williamson (2000), Stroud (2002, 2009, 2011), Unger (1972),and Dretske (1969).

  3. For example, Strawson (1992, 1995) suggests that we cannot understand the concept of perception without reference to the concept of knowledge, and vice-versa.

  4. Stroud (2011) registers this idea in the first three paragraphs of that paper, building on from his (2009) work on skepticism about perceptual knowledge of the world. Moreover, although Stroud’s reasons are different from Dretske’s, Dretske expresses a similar idea in his (2010) contribution to A Companion to Epistemology (2nd ed). For a discussion on how theories of propositional perception make contact with skepticism, see Cassam (2007b(Chap. 1), 2009), McDowell (1994, 2008), and Stroud (2011).

  5. Several epistemologists (Sosa 2007; Greco 2003; Pritchard 2005) think that the anti-luck intuition on knowledge is grounded in some such intuition about how knowledge is a kind of achievement. Cf. Prichard (2007, p. 277) for a detailed expression of this intuition.

  6. Cf. Dancy (1985, p. 134): “[J]ustification and knowledge must somehow not depend on coincidence or luck. This was just the point of the Gettier counterexamples; nothing in the tripartite definition excluded knowledge by luck”. See also Pritchard (2013), where he argues against some recent attempts to show that knowledge is compatible with epistemic luck.

  7. Both Millar (2008) and Cassam (2008) advance this kind of response. Their motivation is not to preserve the Entailment Thesis per se, however, since their motivation is just to describe the relationship between visual perception and knowledge, where a consequence is the truth of the Entailment Thesis. For Millar at least, environments with multiple ringers prevents one from exercising their relevant “recognitional capacities” and it’s this which prevents the agent in barn-type cases from seeing that a barn is in front of them. Cassam, on the other hand, just seems to maintain that it’s because S can’t know in barn-type cases which prevents S from seeing that a barn is there as well, given that seeing that p is a way of coming to know that p. See (Millar (2008), pp. 333–337), and (Cassam (2008), pp. 38–41), in particular.

  8. For an interesting discussion on different theories of propositional perception and their relation to perceptual experience, see French (2013). Moreover, French (2012) argues against Turri (2010) arguments against the Entailment Thesis. But French appeals to broadly linguistic considerations, while in this paper I am appealing to broadly epistemological considerations. In fact, it would be interesting to see how one’s theory of the nature of propositional perception informed how one ought to respond to the three general arguments I discuss in this paper. For example, Craig French point out that if we think of the nature of propositional perception as a propositional-perceptual state, where there need be no necessary epistemic conditions on its obtaining, then the worry with the Straightforward Response from Sect. 2 seems to be a good one. On the other hand, if we think of the nature of propositional perception as a epistemic-perceptual state—that is, as having epistemic conditions, such as putting the perceiver in a position to know that p for its obtaining—then the Straightforward Response looks more plausible for the proponent of this view of the nature of propositional perception.

  9. (Pritchard (2011), pp. 442–443) and (McDowell (2002), p. 277) makes this point [indeed, the case McDowell gives is structurally analogous to (Turri (2010), p. 199) “Rabbit” case] where the agent in McDowell’s case believed that the object merely appeared green because he justifiedly thought it was under a color distorting light, even though he later discovers there was no such light, and he actually saw that it was green.

  10. Nozick’s expression of this condition was in terms of the subjunctive conditional: \({\sim } \mathrm{p} \square \rightarrow {\sim }\) B(p). That is, if p were false, I wouldn’t believe that p. He later refines the principle in his (1981, Chap. 3, §III), relativizing it to an epistemic basis. On this model, where \(b\) is a basis for belief, the condition would read: \({\sim } \hbox {p} \square \rightarrow {\sim }\) B(p) on basis \(b\).

  11. The complications with sensitivity are not relevant for our purposes, so I’ll only briefly register them here. The complications include the possibility of inductive knowledge, Sosa (1999) ‘Garbage Chute’ case, and the denial of the Closure Principle on knowledge (roughly, the principle that if S knows that \(p\), and S knows that \((p \vdash q)\), then S knows that \(q))\). Also, note that I am avoiding interesting issues about whether or not either of sensitivity or safety, however formulated, really does articulate the anti-luck condition on knowledge. There are arguments on offer for the claim that, while propositional knowledge excludes epistemic luck, neither of safety nor sensitivity in any of their formulations properly expresses the anti-luck condition. See Hiller and Neta (2007), Vogel (2007), and Lackey (2008).

  12. I want to register that there are at least three different expressions of the safety condition on offer. Here’s Williamson’s (2000, p. 147) version: “if one knows, one could not easily have been wrong in a similar case”. Pritchard (2007, p. 281): “S’s belief is safe iff in most near-by possible worlds in which S continues to form her belief about the target proposition in the same way as in the actual world the belief continues to be true”. And Sosa (1999, p. 146): “If S were to believe that p, p would be true”, though Sosa relativizes safety to a basis later in his (2007).

  13. This distinction can be found in Pritchard (2005), and first in Engel (1992) as the distinction between evidential luck and veritic luck. See also Unger (1968) for three other distinctions between types of luck, none of which, he argues, are incompatible with knowledge.

  14. Nozick relativizes sensitivity to an evidential basis in his (1981 p. 179)

  15. Perhaps one will agree with me that in BARN, S satisfies the anti-luck conditions on knowledge, but nevertheless maintain that S still fails to know that a barn is in front of them for other reasons independently of the anti-luck conditions. At this juncture, the proponent of the Entailment Thesis could then mount the Straightforward Response. After all, this is compatible with the argument against the Argument from Luck that I provided being successful. Thanks to an anonymous reviewer for this helpful suggestion.

  16. Cf. Unger (1968), Engel (1992), and Pritchard (2004, 2005, 2013). For discussion, see Engel (2011).

  17. This premise is drawn out from the following quotation from Pritchard (2011): “But now suppose further that one has been told, by an otherwise reliable informant, that one is presently being deceived (that one is in barn facade county, say), even though this is in fact not the case. Clearly, in such a case one ought not to believe the target proposition [...]” (ibid.).

  18. I draw out (EPISTEMIC OUGHT) from the remaining quotation in footnote 12 of Pritchard (2011): “[...] and hence one cannot possibly know this proposition either. (Indeed, if one did continue to believe the target proposition even despite the presence of this undefeated defeater, then one would still lack knowledge).” In any case, the Argument from Defeat would be fallacious without this principle in play.

  19. Let’s make clear a certain ambiguity in this principle. Let O be a deontic operator for ‘ought’, and B be the belief predicate. From O(S, \(\sim \)B[p]) it does not follow that O(S, B[\(\sim \)p]), nor does it follow from \(\sim \)O(S, B[p]) that O(S, \(\sim \)B[p]). In \(\sim \)O(S, B[p]), the negation operator is ranging over the ought operator, whereas in O(S, \(\sim \)B[p]) the negation operator is ranging over the belief predicate. In the first case, what ought not be the case is S believing that p. In the second case, what ought to be the case is S not believing that p. The (\(-\)EPISTEMIC OUGHT IMPLIES CAN) principles’ antecedent says that what ought to be the case is S withholding belief that p, that is, not believing that p. So, the (\(-\)EPISTEMIC OUGHT IMPLIES CAN) principle says that O(S, \(\sim \)B[p]) \(\rightarrow \lozenge \sim \)B(S, p). The intuitiveness of this principle, I take it, derives from the analogous ethical principle that, if what ought to be the case is S not \(\upphi \)ing, then it has to at least be logically possible for S not to \(\upphi \). After all, if one’s ethical principle entailed that everyone ought to successfully divide by zero, even though no one could ever successfully divide by zero, that would just be a bad ethical principle: it would entail that we should do what we cannot do. Here, I am just taking it that the same is true for normative epistemological principles.

  20. For the full examples, see (Turri (2010), pp. 198–199).

  21. Why might one think the Entailment Thesis is non-negotiable? Well, one could maintain that it is part of the concept of propositional perception that it has certain necessary epistemological conditions, such as knowing that p. Cf. (Cassam (2008), p. 38), where he discusses this idea. Note that their discussion does not bear directly on the present concern in the text, but one does find expression of the idea that propositional knowledge is a necessary condition of propositional perception. The core thought in the text, however, is that, insofar as we think we can and often do see that such and such is so in the world around us, then because knowing that such and such is so is a necessary condition of that kind of perceptual state, the Entailment Thesis is, in consequence, non-negotiable. A similar thought for the Knowledge Entails Belief principle might run like this: it is because we can and often do know that such and such is so, and because it is a necessary condition of this state being instantiated that we believe that such and such is so, that the Knowledge Entails Belief principle is non-negotiable. What I am doing in the main body of the text is just highlighting how the reasoning on this score might run along the same lines, and so simply appealing to either of these principles alone, plus the relevant premise in the Argument from Belief, will be no more effective than, or at least as effective as, the other principle. The thought here is that both moves are available because one can, at least on the surface, consistently maintain that either principle is non-negotiable, so a simple appeal to one principle over the other will remain an ineffective dialectical move, as made more explicit in Sect. 4.1.

  22. To be sure, most epistemologists do take the Knowledge Entails Belief principle to be non-negotiable. But there is also a long epistemological tradition which questions this principle. See Plato’s Republic, pp. 476–479, Prichard (1950), Woozley (1953), and Radford (1966).

  23. Cf. Campbell (1967), Audi (1994), and Schwitzgebel (2010) for this distinction. For the literature on whether or not knowledge entails occurrent belief or acceptance, see: Armstrong (1969), Black (1971), and Radford (1970, 1990).


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I would like to thank Duncan Pritchard, Allan Hazlett, the Edinburgh Epistemology Research Group, and the Editors of Synthese for comments and suggestions on earlier versions of this paper. I would also like to thank Barry Stroud for helpful discussion on the issues I raised in this paper. I am especially indebted to Craig French, whose detailed and insightful comments on an early version of this paper helped improve it substantially.

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Ranalli, C. Luck, propositional perception, and the Entailment Thesis. Synthese 191, 1223–1247 (2014).

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  • Entailment Thesis
  • Belief
  • Luck
  • Propositional perception
  • Barn-cases
  • Knowledge