In defense of proper functionalism: cognitive science takes on Swampman


According to proper functionalist theories of warrant, a belief is warranted only if it is formed by cognitive faculties that are properly functioning according to a good, truth-aimed design plan, one that is often thought to be specified either by intentional design or by natural selection. A formidable challenge to proper functionalist theories is the Swampman objection, according to which there are scenarios involving creatures who have warranted beliefs but whose cognitive faculties are not properly functioning, or are poorly designed, or are not aimed at truth. In this paper, we draw lessons from cognitive science in order to develop a novel argument for the conclusion that the Swampman objection fails against proper functionalist theories of warrant. Our argument not only shows that the underlying, central intuition motivating Swampman-like scenarios is false but also motivates proper function as a necessary condition for warrant, thereby lending support to the claim that any theory of knowledge that lacks a proper function requirement is false.

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  1. 1.

    Although we are specifically responding to the Swampman objection as it applies to a proper functionalist theory of warrant, our response also provides resources for someone who is defending a proper functionalist theory of justification. See footnote 15 for more discussion of this point. Furthermore, the Swampman objection could be applied to any etiological theory of any epistemic property; our response may provide resources for defending those theories as well.

  2. 2.

    Klein (1996), Markie (2004, p. 538), and Goldman (2009, p. 248) also wield versions of the Swampman objection to proper functionalism.

  3. 3.

    Plantinga (1991, pp. 206–208; 1993b, pp. 76–77) and Graham (2012, pp. 466–467). They are joining a chorus of philosophers of mind who doubt that Swampman could have representational contents and beliefs in the first place. Indeed, this is what Davidson was arguing for when he first presented the Swampman scenario! However, many in both the philosophy of mind and epistemology literatures think that Swampman would have beliefs, and so our paper engages with those philosophers. Thanks to a referee for a helpful note on this point.

  4. 4.

    Plantinga (1991, pp. 208–209; 1993b, p. 78) and Graham (2014).

  5. 5.

    Boyce and Plantinga (2012, pp. 130–131) and Cf. McNabb (forthcoming).

  6. 6.

    In addition to Bergmann, a number of epistemologists have endorsed the claim that fittingness is contingent, including Plantinga (1993a, pp. 98–99), Greco (2000, pp. 173–174), Markie (2004, pp. 530–533; 2006, pp. 118–119) and Lyons (2013, pp. 13–21). Its roots can be traced as far back as Reid (1764/1997, p. 57).

  7. 7.

    From here on, we will leave the “and justified” implicit.

  8. 8.

    Proof: Assume for conditional proof that S* comes to hold belief B in the same way that another subject S does in a relevantly similar environment and that B is not warranted for S*. Assume for reductio that B is warranted for S. It follows from CI that B is warranted for S* (since S* forms her belief in the same way that S does in a relevantly similar environment). Contradiction! It follows by reductio ad absurdum that B is not warranted for S. It further follows by conditional proof that if S* comes to hold B in the same way that S does in a relevantly similar environment and B is not warranted for S*, then B is not warranted for S.

  9. 9.

    This includes a referee, who provided significant and helpful contribution to the contents of this paragraph, including the following two responses.

  10. 10.

    See Rosander and von Hofsten (2004) and von Hofsten et al. (2007). These experiments are on the basis of eye tests, where experimenters trace the infant’s eye movement. See also Baillargeon (1987) for further evidence.

  11. 11.

    See Spelke and von Hofsten (2001) and Hespos et al. (2009) for evidence and discussion.

  12. 12.

    See Piaget’s (1954) classic study on this topic. Many were influenced by Piaget to think that object permanence did not develop until 9 months. It is the more recent studies, cited in the previous footnotes, that swung the majority of developmental psychologists to believe otherwise.

  13. 13.

    There are interesting issues about the connection between the beliefs of these infants and the various behaviors indicating the presence of these beliefs. See Young (2005) and Hespos et al. (2009) for interesting discussion.

  14. 14.

    Plantinga (1993a, pp. 33–37) has proposed that this sort of accidentality be analyzed in terms of lack of proper function. (See also Boyce and Plantinga 2012, pp. 127–128.) However, we needn’t accept this general claim in order to accept the intuitive judgment that Billy’s belief is accidentally true in a knowledge precluding way in this particular case.

  15. 15.

    Note that we are talking about warrant, not justification. Some internalists might think that both Billy’s and Zork’s beliefs are justified and still agree with us that the belief is unwarranted. For example, phenomenal conservatives will likely think that both beliefs are justified because it seems to both Billy and Zork that the round object they saw has ceased to exist (and they have no defeaters). In fact, phenomenal conservatives like Tucker (2011) and Huemer (2013, pp. 747–748) have pointed to cases like these as instances of justified but unwarranted belief. On the other hand, externalists like Boyce and Plantinga (2012) and Bergmann (2013) are likely to just think that the belief is also unjustified. Regardless of that debate between internalists and externalists about justification, we expect wide agreement from both camps about the warrant-appropriateness of these beliefs.

  16. 16.

    We thank a referee for help thinking through the contents of this paragraph.

  17. 17.

    We thank a referee for help in clarifying the moves made in these final paragraphs of the paper.

  18. 18.

    One could also reply that we are inclined to say that Billy doesn’t know because he doesn’t have what Sosa calls reflective knowledge or knowing full well, even though he does in fact have animal knowledge. But we have argued that Billy does not have knowledge, and since animal knowledge is a type of knowledge, it follows that he also does not have animal knowledge. Furthermore, this reply does not do justice to the fact that it seems that Zork does know and Billy doesn’t, despite the fact that neither has the higher-level reflective competences required for reflective knowledge and knowing full well. So, one cannot explain why we are inclined to think that Billy doesn’t know by appealing to his lacking higher levels of knowledge, since Zork lacks those levels too.


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We are grateful to Sarah Boyce, Matthew Lee, Josh May, Matthew McGrath, Alvin Plantinga, Ted Poston, and Ernie Sosa for helpful correspondence and conversation concerning these matters. We are also thankful to the audience at the 2015 MidSouth Philosophy conference, including Matthew Frise, Derek Jones, Kevin McCain, Alex Radulescu, Josh Smart, and especially our commentator Nick Byrd.

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Correspondence to Andrew Moon.

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Boyce, K., Moon, A. In defense of proper functionalism: cognitive science takes on Swampman. Synthese 193, 2987–3001 (2016).

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  • Swampman
  • Warrant
  • Knowledge
  • Proper functionalism