Abstract
The philosophy literature is rife with thought experiments, and quite recherché thought experiments at that. Derek Parfit’s Reasons and Persons, arguably the most influential work on personal identity in the last 50 years, walks readers through cases of teletransportation, gradual matter reorganizers, brain transplants, fission, and so on. Other famous thought experiments ask us to imagine a man shuffling papers in a room to implement a Chinese-speaking computer program; or “people seeds” that float in past your window screens and lead to a person blooming on your sofa; or a neuroscientist confined to a black and white room who nonetheless learns the complete (and finished) neuroscience of color vision. But while these evocative, rich cases have spawned a huge literature, it is a recurring complaint that we should not settle debates in philosophy using such recherché thought experiments.
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Notes
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Your philosophical zombie twin is a molecule-for-molecule duplicate of you that lacks consciousness. The zombie thought experiment is supposed to show that physicalism is false. Patricia Churchland (1996) voices concern about the effectiveness of zombie thought experiments on behalf of neuroscientists, calling it the “hornswoggle problem.” Of course I exaggerate in suggesting that by some philosophers’ lights, all the lab work is “a waste”; but those philosophers contend that zombie thought experiments do show that lab work cannot answer certain critical, central questions about consciousness.
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Gettier’s (1963) cases feature subjects with true beliefs, where it seems like the subject arrived at the truth by accident; they are intended to show that knowledge requires more than justified true belief. Here’s an example, based on Chisholm (1989): you look at a hill from a distance and see something that looks like a sheep. You thereby come to believe there is a sheep on the hill. But it turns out you were looking at a vaguely sheep-shaped rock, and not a sheep. However, there is a sheep on the other side of the hill, completely hidden from your line of sight. Your belief is true and justified, but only accidentally true, and so the suggestion goes, not knowledge.
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Thomson (1971) offers her violinist case to show that abortion is permissible, at least in some cases, even if one grants that the unborn is a person. You are kidnapped and hooked up to a famous violinist with a kidney ailment, whose survival for the next 9 months medically depends on remaining connected to you. It seems clear to Thomson that it is permissible to unplug yourself from the violinist; the violinist has a right to life, she argues, but not to your body, The people seed case is a bit more bizarre: “Again, suppose it were like this: people-seeds drift about in the air like pollen, and if you open your windows, one may drift in and take root in your carpets or upholstery. You don't want children, so you fix up your windows with fine mesh screens, the very best you can buy. As can happen, however, and on very, very rare occasions does happen, one of the screens is defective; and a seed drifts in and takes root. Does the person-plant who now develops have a right to the use of your house? Surely not—despite the fact that you voluntarily opened your windows, you knowingly kept carpets and upholstered furniture, and you knew that screens were sometimes defective” (p. 59).
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Thanks to Amy Kind for pointing out these two cases (see also Wilkes 1988) and for pressing me to clarify the recherché puzzle.
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Explicit defenders of imagining as a guide to possibility include Yablo (1993, 2006), Chalmers (2002), Geirsson (2005), Gendler (2000), Gregory (2004), Hart (1988), Hill (1997), and Kung (2010). Many, many others assume it without argument, e.g., from (famously) Hume (1978) to Nagel (1974) to Lewis (1986).
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See my (2011).
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I offer such a theory in Kung (2010).
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Throughout the chapter, by “possibility” I mean metaphysical possibility.
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The meaning of “demonstrative certainty” is a matter of some debate among Hume scholars; see Belshaw (1989).
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See, e.g., Ichikawa and Jarvis (2012).
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Chalmers (2002) writes, “There is a sense in which we can imagine situations that do not seem to be potential contents of perceptual experiences… In [some] cases, we do not form a perceptual image that represents S. Nevertheless, we do more than merely suppose that S, or entertain the hypothesis that S… We might say that in [some] cases, we can modally imagine that [S]… Modal imagination goes beyond perceptual imagination…but it shares with perceptual imagination its mediated objectual character” (p. 151). See also Yablo (1993) and Walton (1990).
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Amy Kind and I articulate this puzzle in our (2016).
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See Langland-Hassan (2016).
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The principle may not be as strong as it initially seems, because for Hume the ideas involved in the conceiving have to be adequate. Adequacy is a technical term among the moderns, and there is some debate about how to interpret Hume’s use of the term. See Kail (2003).
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For example: “If one is to establish by means of a FSE [Frankfurt Style Example] that people can exercise their will without there being an available alternative sequence in which they do not so exercise their will, then that FSE must express a metaphysical possibility” (Cain 2003, p. 221). Some other examples include Pryor (2000, p. 524) and Taliaferro (1986, p. 95).
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The claim that impressions are actual, or, more precisely, that what the impression is of is actual, needs some qualification. Some interpreters regard Hume as a thoroughgoing skeptic about extramental reality; if that is correct, then we cannot know whether impressions are actual. Other interpreters see Hume as a skeptical realist, who claim that we can have only limited knowledge of extramental reality. See Kail (2003) for discussion in the case of necessary connection. For our purposes, we can grant that impressions are actual because denying it is tantamount to external world skepticism, and it would be no surprise if we couldn’t solve the skeptical challenge to modal epistemology when we cannot solve it for epistemology generally.
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The term “reality congruent” is from Van Leeuwen (2016, p. 9).
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Though see the qualification in note 22.
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See Kung (2010) for my attempt to do so.
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See footnote 22.
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Of course the other elements in the imagining must meet the same standard. Imagining Bill Clinton giving his new granddaughter a round square to play with doesn’t show that round squares are possible.
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See point three below.
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Pretty much every episode of Star Trek invites us to imagine this way.
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There is also an additional worry that in some cases, we might be able to imagine both the yes and no answers to the questions we pose to ourselves. We can imagine the person coming out of the teletransporter is me, and I can imagine that the person coming out of the teletransporter is not me. Combine that with an unrestricted imagination-possibility principle and you have problems.
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One might wonder whether it is possible to reconcile Kripke’s insights with Hume’s theory of imagination and Hume’s modal epistemology. Perhaps the way to do it would be to note that on Hume’s view, the distinction between imagining Hesperus and imagining a Hesperus-like appearance is fuzzy at best: imagination under the picture theory of ideas will treat them similarly. Some of the very reasons that motivate a move away from the picture theory might help the picture theory cope with Kripke cases.
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I discuss and argue against the error theory elsewhere; see Kung (2014).
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Again, there is a lot more to say about Kripke cases. See my (2014) for further discussion.
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This chapter had two sources of inspiration. The first was Peter Thielke’s unpublished paper, “Naturalism and rationalism on the tines of Hume’s fork,” which inspired me to look for hidden commitments in Hume’s modal epistemology. The second inspiration was the introduction that Amy Kind and I cowrote for our edited volume Knowledge Through Imagination. I am grateful to Peter and Amy for both inspiration and for discussion of this piece. Many thanks also for helpful feedback to Felipe Leon, Jennifer Nado, Nico Silins, and the audience at the 2015 Forefronts of Epistemology workshop at Kyoto University.
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Kung, P. (2017). Personal Identity Without Too Much Science Fiction. In: Fischer, B., Leon, F. (eds) Modal Epistemology After Rationalism. Synthese Library, vol 378. Springer, Cham. https://doi.org/10.1007/978-3-319-44309-6_8
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