How to demarcate the boundaries of cognition


Advocates of extended cognition argue that the boundaries of cognition span brain, body, and environment. Critics maintain that cognitive processes are confined to a boundary centered on the individual. All participants to this debate require a criterion for distinguishing what is internal to cognition from what is external. Yet none of the available proposals are completely successful. I offer a new account, the mutual manipulability account, according to which cognitive boundaries are determined by relationships of mutual manipulability between the properties and activities of putative components and the overall behavior of the cognitive mechanism in which they figure. Among its main advantages, this criterion is capable of (a) distinguishing components of cognition from causal background conditions and lower-level correlates, and (b) showing how the core hypothesis of extended cognition can serve as a legitimate empirical hypothesis amenable to experimental test and confirmation. Conceiving the debate in these terms transforms the current clash over extended cognition into a substantive empirical debate resolvable on the basis of evidence from cognitive science and neuroscience.

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  1. 1.

    Throughout the paper, I will use ‘component’ to refer specifically to parts of a mechanism, system, object, or process bearing appropriate relationships of mutual manipulability to the phenomenon as a whole (“The mutual manipulability criterion” section). Consequently, not every arbitrarily subdivided part of a given object will count as a component. See Craver (2007b) for similar treatment. One exception will be in “The Simon-Haugeland bandwidth criterion” section, where Haugeland’s alternative views about individuating system components and boundaries are discussed.

  2. 2.

    The second aspect of their criterion—that cognition involves a distinctive form of causal process—is also problematic, and has been subject to a number of challenges including Clark (2005, 2008). For brevity, I focus only on problems associated with the first aspect.

  3. 3.

    See Dennett (1987) for original critical discussion. For more recent discussion of non-derived content in the context of the EC debate, see Clark (2005, 2008). For a rebuttal, see Adams and Aizawa (2008).

  4. 4.

    It should be acknowledged that Clark (2008) explicitly denies that the parity principle operates as anything more than a heuristic device or “intuitive probe” to loosen commitments to the idea of a skin/skull boundary for cognition. However, it is as close as defenders of EC come to offering an explicit demarcation criterion. Rowlands (2010) is one notable exception.

  5. 5.

    Shear force is defined as a force applied parallel or tangential to the surface of a given material. In this context, it increases the animal’s resistance to sliding along a surface.

  6. 6.

    Surface energy describes the disruption of intermolecular bonds occurring at the surface of a liquid or solid.

  7. 7.

    See Craver (2007b) for further discussion.

  8. 8.

    Clark and Chalmers emphatically announce: “[w]e cannot point to the skin/skull boundary as justification [for the boundaries of cognition], since the legitimacy of that boundary is precisely what is at issue” (1998, 8). Critics of EC are thus understandably reluctant to employ spatial criteria to delimit cognitive boundaries so as to avoid charges of question-begging.

  9. 9.

    Adams and Aizawa (2008) pose several additional challenges for Haugeland’s criterion. Adequately addressing their arguments against Haugeland’s account, however, goes beyond the scope of this paper.

  10. 10.

    Thanks to Georg Theiner for bringing Clark’s discussion to my attention.

  11. 11.

    Grush (2003) proposes the plug points criterion as a means of delimiting boundaries along similar lines.

  12. 12.

    Although manipulability theories of causal explanation are commonly expressed using variables, one should not infer that such accounts are committed to causal relationships holding between “abstracta” rather than objects and properties in the world. See Craver (2007a, 94–95) and Woodward (2003, 14) for further discussion.

  13. 13.

    The term ‘level’ here means mechanistic level, i.e., the set of component parts and activities responsible for producing a phenomenon or performing some higher-level role (Craver 2007a, b). Lower mechanistic levels bear a compositional relationship to higher mechanistic levels in the sense that lower-level parts are components of the mechanism for a phenomenon at some higher level. A crucial feature of mechanistic levels is that they support recursive decomposition. The activities of components in a mechanism responsible for some phenomenon (constituting one mechanistic level) can themselves be viewed as phenomena to be explained, and still lower-level activities and entities can subsequently be identified in their explanations.

  14. 14.

    One might reasonably wonder about the relevant timescales for assessing relationships of mutual manipulability. Because the mutual manipulability account takes direct guidance from scientific practice, answers about the timescales over which such relationships operate will ultimately be guided and constrained by the relevant science. Since this paper focuses on EC claims in certain sectors of cognitive science and neuroscience, the relevant timescales are primarily organismal ones (e.g., developmental, behavioral, and neural). It is, however, beyond the scope of the paper to defend this proposition in any detail or address how the current account handles relationships that occur more slowly over generational and evolutionary timescales such as cumulative changes in technologies and other forms of cognitive scaffolding in human physical and social environments. I thank an anonymous reviewer for raising this issue.

  15. 15.

    Bechtel and Richardson (1993), Craver and Darden (2001), and Craver (2002) have also discussed these experimental strategies and the critical role they play in the development of mechanistic explanations.

  16. 16.

    It should be noted that intra-level interventions (intervention and observation at the same mechanistic level) do sometimes play a limited role in establishing componency claims. They can help to refine our characterizations of the phenomenon to be explained and improve our understanding of the organization of components and their activities within one mechanistic level. Nevertheless, intra-level experiments are primarily useful for testing standard etiological-causal claims (e.g., speeding up reaching movements causes increased endpoint variance; increasing cognitive load increases reaction times; increasing the flow of Na+ into a neuron causes Na+ channels to open, etc.); and inter-level interventions remain the principal means by which componency claims are tested and confirmed. See Craver (2007a, b) for further discussion.

  17. 17.

    One might object that preventing blood flow to a region would quickly degrade task performance, perhaps along with other long-term consequences, and thus this process should count as a component. However, because regional increase in cerebral blood flow temporally lags behind neural activation by some small amount, it is safe to assume that preventing those changes cannot, strictly speaking, alter either neural activation or the task performance it supports. An ideal intervention to selectively suppress only the time-lagged hemodynamic response following activation would demonstrate this.

  18. 18.

    Muscles, like springs, vary in stiffness. Applying the same load force to two springs of varying thicknesses will produce different increases in spring length directly proportional to their thickness (i.e., a thick spring will increase its length less than a thin one).

  19. 19.

    It should be noted that additional control experiments were conducted to rule out alternative explanations for degraded performance such as lower visual resolution across the entire workspace due to enforced central fixation. See Ballard et al. (1995) for further details.


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Thanks to Jake Beck, Carl Craver, Philip Gerrans, Peter Langland-Hassan, Gerard O'Brien, and Gualtiero Piccinini for helpful comments on previous drafts of this paper. Thanks also to an anonymous reviewer and the editor at the journal for constructive feedback.

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Correspondence to David Michael Kaplan.

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Kaplan, D.M. How to demarcate the boundaries of cognition. Biol Philos 27, 545–570 (2012).

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  • Extended cognition
  • Embodied cognition
  • Mutual manipulability
  • Intervention
  • Mechanism