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Tentative Resolution

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Notes

This section presents Steve’s current guess at the truth. The guess is offered as an idea for further consideration and is unlikely to be correct.

Physical intuitions are reliable—but only within limits

Non-experts have incorrect physical intuitions. To illustrate, they will reliably judge that a projectile exiting a spiral tube will subsequently follow a spiral trajectory (McCloskey, Caramazza, & Green, 1980). Why?

Sometimes when adult humans observe a moving object that disappears, they will misremember the location of its disappearance in way that reflects its momentum; this effect is called representational momentum (Freyd & Finke, 1984; Hubbard, 2010).

The trajectories implied by representational momentum reveal that the effect reflects impetus mechanics rather than Newtonian principles (Freyd & Jones, 1994; Kozhevnikov & Hegarty, 2001; Hubbard, Blessum, & Ruppel, 2001; Hubbard, 2013). And these trajectories are independent of subjects' scientific knowledge (Freyd & Jones, 1994; Kozhevnikov & Hegarty, 2001). Representational momentum therefore reflects judgement-independent expectations about objects’ movements which track momentum in accordance with a principle of impetus.[1]

We might therefore conjecture that physical intuitions are based on impetus mechanics. This would explain the spiral trajectory judgements observed by (McCloskey et al., 1980).

Why is this significant? Impetus mechanics makes computing trajectories and other physical quantities relatively fast (compared to Newtonian mechanics).[2] Impetus mechanics is also reliable within a limited but useful range of situations—those in which objects move horizontally rather than vertically, gravity is unchanging, and so on. So impetus mechanics was all humans needed for nearly all of the last few hundred thousand years. Only recent technological changes expose the limits of physical intuitions.

Conclusion: physical intuitions are reliable enough to be a source of knowledge—but only within limits. Their reliability is limited to situations that were frequent and significant in human experience over evolutionary timescales.

Limits of ethical intuitions

Like physical intuitions, ethical intuitions are likely reliable only in situations that were frequent and significant in humans’ evolutionary history. (This is probably true of intuitions generally.)

Ethical intuitions are probably reliable enough to ground knowledge of ethics concerning matters such as food sharing in small bands and cooperative breeding.

They are unlikely to be reliable enough to ground ethical knowledge concerning matters that were not frequent and significant in humans’ evolutionary history.

This includes trolley problems. Filial infanticide aside,[3] decisions involving harming one to save others have probably been as rare in humans’ history as reliance on recent discoveries to construct such scenarios hints (Greene, 2014, p. 252).[4]

Conclusion

Those who defend ethical intutions are right insofar as intuitions are a reliable source of knowledge in a limited but useful range of situations.

Those who attack ethical intutions are right that ethical intutions are not a source of knowledge concerning the things that philosophers are interested in. (That said, it is not the influence of extraneous factors which makes intutions too unreliable to be a source of knowledge; nor does the existence of inconsistent intuitions between cultures demonstrate this—see Moral Knowledge Does Exist.)

Relying on intuitions for ethical knowledge in philosophy is probably always a mistake because philosophers are mostly interested in novel problems, such as climate change or global poverty, or very general theories, such as a theory of justice.

Relying on ethical intuitions to establish a theory of justice would be like relying on physical intuitions to land a robot on a comet.

Glossary

David : ‘David is a great transplant surgeon. Five of his patients need new parts—one needs a heart, the others need, respectively, liver, stomach, spleen, and spinal cord—but all are of the same, relatively rare, blood-type. By chance, David learns of a healthy specimen with that very blood-type. David can take the healthy specimen's parts, killing him, and install them in his patients, saving them. Or he can refrain from taking the healthy specimen's parts, letting his patients die’ (Thomson, 1976, p. 206).
Edward : ‘Edward is the driver of a trolley, whose brakes have just failed. On the track ahead of him are five people; the banks are so steep that they will not be able to get off the track in time. The track has a spur leading off to the right, and Edward can turn the trolley onto it. Unfortunately there is one person on the right-hand track. Edward can turn the trolley, killing the one; or he can refrain from turning the trolley, killing the five’ (Thomson, 1976, p. 206).
representational momentum : Sometimes when adult humans observe a moving object that disappears, they will misremember the location of its disappearance in way that reflects its momentum (Freyd & Finke, 1984; Hubbard, 2010). There are several competing models of representational momentum and related phenomena involving misremembered location (Hubbard, 2010).
trolley problem : ‘Why is it that Edward may turn that trolley to save his five, but David may not cut up his healthy specimen to save his five?’ (Thomson, 1976, p. 206).

References

Descartes, R. (1998). The world and other writings. (S. Gaukroger, Ed.). Cambridge: Cambridge University Press.
Freyd, J. J., & Finke, R. A. (1984). Representational momentum. Journal of Experimental Psychology: Learning, Memory, and Cognition, 10(1), 126–132. https://doi.org/10.1037/0278-7393.10.1.126
Freyd, J. J., & Jones, K. T. (1994). Representational momentum for a spiral path. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20(4), 968–976. https://doi.org/10.1037/0278-7393.20.4.968
Garn, S. M., & Block, W. D. (1970). The Limited Nutritional Value of Cannibalism. American Anthropologist, 72(1), 106–106. https://doi.org/10.1525/aa.1970.72.1.02a00140
Greene, J. D. (2014). Moral tribes: Emotion, reason and the gap between us and them. New York: Atlantic Books.
Hrdy, S. B. (1979). Infanticide among animals: A review, classification, and examination of the implications for the reproductive strategies of females. Ethology and Sociobiology, 1(1), 13–40. https://doi.org/10.1016/0162-3095(79)90004-9
Hrdy, S. B. (2011). Mothers and others: The evolutionary origins of mutual understanding. Cambridge, Massachusetts: Belknap Press.
Hubbard, T. L. (2005). Representational momentum and related displacements in spatial memory: A review of the findings. Psychonomic Bulletin & Review, 12(5), 822–851. https://doi.org/10.3758/BF03196775
Hubbard, T. L. (2010). Approaches to representational momentum: Theories and models. In R. Nijhawan & B. Khurana (Eds.), Space and time in perception and action. Cambridge: Cambridge University Press.
Hubbard, T. L. (2013). Launching, Entraining, and Representational Momentum: Evidence Consistent with an Impetus Heuristic in Perception of Causality. Axiomathes, 23(4), 633–643. https://doi.org/10.1007/s10516-012-9186-z
Hubbard, T. L., Blessum, J. A., & Ruppel, S. E. (2001). Representational momentum and Michotte’s “launching effect” paradigm (1946/1963). Journal of Experimental Psychology: Learning, Memory, and Cognition, 27(1), 294–301. https://doi.org/10.1037/0278-7393.27.1.294
Kozhevnikov, M., & Hegarty, M. (2001). Impetus beliefs as default heuristics: Dissociation between explicit and implicit knowledge about motion. Psychonomic Bulletin & Review, 8(3), 439–453. https://doi.org/10.3758/BF03196179
McCloskey, M., Caramazza, A., & Green, B. (1980). Curvilinear Motion in the Absence of External Forces: Naive Beliefs about the Motion of Objects. Science, 210(4474), 1139–1141. https://doi.org/10.2307/1684819
Moletti, G. (2000). The Unfinished Mechanics of Giuseppe Moletti: An Edition and English Translation of His Dialogue on Mechanics, 1576, translated by W. R. Laird. Toronto: University of Toronto Press.
Rodríguez, J., Guillermo, Z.-R., & Ana, M. (2019). Does optimal foraging theory explain the behavior of the oldest human cannibals? Journal of Human Evolution, 131, 228–239. https://doi.org/10.1016/j.jhevol.2019.03.010
Thomson, J. J. (1976). Killing, Letting Die, and The Trolley Problem. The Monist, 59(2), 204–217. https://doi.org/10.5840/monist197659224

Endnotes

  1. Note that momentum is only one of several factors which may influence mistakes about the location at which a moving object disappears. See Hubbard (2005, p. \ 842): ‘The empirical evidence is clear that (1) displacement does not always correspond to predictions based on physical principles and (2) variables unrelated to physical principles (e.g., the presence of landmarks, target identity, or expectations regarding a change in target direction) can influence displacement. [...] information based on a naive understanding of physical principles or on subjective consequences of physical principles appears to be just one of many types of information that could potentially contribute to the displacement of any given target' ↩︎

  2. See Kozhevnikov & Hegarty (2001, p. 450): To extrapolate objects’ motion on the basis of [e.g. Newtonian] physical principles, one should have assessed and evaluated the presence and magnitude of such imperceptible forces as friction and air resistance [...] This would require a time-consuming analysis that is not always possible. In order to have a survival advantage, the process of extrapolation should be fast and effortless, without much conscious deliberation. Impetus theory allows us to extrapolate objects’ motion quickly and without large demands on attentional resources.’ ↩︎

  3. Hrdy (1979); Hrdy (2011) reviews evidence on the prevalence and causes of filial infanticide in humans. Although important in many ways for understanding humans’ moral intuitions, filial infanticide can be set aside here as the special circumstances in which it routinely occurs (in the first hours after giving birth and where there is a perceived lack of social support) indicate that it is unlikely to be a source of representative experience (Hrdy, 1979; Hrdy, 2011). ↩︎

  4. Could nutritional cannibalism have been a significant source of representative experience and valid feedback? This turns out to be unlikely. Humans were historically insufficiently nutritious to make cannibalism worthwhile, except possibly where death had other causes (Garn & Block, 1970; Rodríguez, Guillermo, & Ana, 2019, p. 236). ↩︎