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.

Key words: extended cognition, embodied cognition, mutual manipulability, intervention, mechanism.

We present a multiscale integrationist interpretation of the boundaries of cognitive systems, using the Markov blanket formalism of the variational free energy principle. This interpretation is intended as a corrective for the philosophical debate over internalist and externalist interpretations of cognitive boundaries; we stake out a compromise position. We first survey key principles of new radical (extended, enactive, embodied) views of cognition. We then describe an internalist interpretation premised on the Markov blanket formalism. Having reviewed these accounts, we develop our positive multiscale account. We argue that the statistical seclusion of internal from external states of the system – entailed by the existence of a Markov boundary – can coexist happily with the multiscale integration of the system through its dynamics. Our approach does not privilege any given boundary (whether it be that of the brain, body, or world), nor does it argue that all boundaries are equally prescient. We argue that the relevant boundaries of cognition depend on the level being characterised and the explanatory interests that guide investigation. We approach the issue of how and where to draw the boundaries of cognitive systems through a multiscale ontology of cognitive systems, which offers a multidisciplinary research heuristic for cognitive science.

Key words: boundaries of cognition, variational free energy principle, externalism, internalism, enactive cognition, embodied cognition, markov blankets.