Content externalism, as we have seen, is best understood as the thesis that some of those mental states that possess their content essentially – namely, propositional attitudes – are individuation dependent on objects, properties, relations and so on occurring outside the skins of the subjects of mental states. As such, content externalism is severely restricted in both its scope and force. It applies neither to cognitive processes nor to the architectures or mechanisms in which those processes are realized. It does not apply to phenomenal states – experiences of various forms – at least not if the essential properties of these states are phenomenal or qualitative rather than propositional or semantic. It applies to some, but only some, propositional attitudes: those whose content is composed of at least one simple rather than complex concept. And even where it does apply, it shows only that these propositional attitudes are externally individuated and not that they are externally located. Content externalism, that is, entails rejection of the internalist Possession Claim but not of the Location Claim.

In Chapters 9 and 10 we look at attempts to broaden the scope and augment the force of externalism. Chapter 10 looks at the possibility of applying externalist principles, broadly understood, to conscious experiences. This chapter, however, focuses on cognitive processes and the architectures that underwrite them. Externalism applied to such items often goes by the name of vehicle externalism: externalism about the vehicles, rather than the contents, of thoughts.