IX—What the Externalist Can Know A Priori

Abstract

ly speaking, externalism is easily enough defined. It is simply the view that facts external to a thinker's skin are relevant to the individuation of (certain of) his mental contents. So stated, externalism does not commit one to any specific form of dependence of mental contents on external facts, just to some form of dependence or other. However, philosophers who embrace externalism don't do so because they regard it as a self-evident truth. They embrace it, rather, 199 This content downloaded from 207.46.13.51 on Mon, 20 Jun 2016 05:55:35 UTC All use subject to http://about.jstor.org/terms 200 PAUL A. BOGHOSSIAN because their intuitive responses to a certain kind of thought experiment -Putnamian Twin Earth fantasiesappear to leave them little choice.2 And that sort of thought experiment motivates externalism only by motivating a specific form of dependence of mental contents on external facts. In particular, it underwrites the claim that, in the case of an atomic, natural kind concept C, the substance actually picked out by C enters into the individuation of C. To put the claim another way: the substances with which a person actually interacts help determine what atomic, natural kind concepts, if any, that person has.3 To see this, let us remind ourselves how the Putnam thought experiment is supposed to work. Whereas Oscar, an ordinary English speaker, lives on Earth, his molecular and functional duplicate, Toscar, lives on Twin Earth, a planet just like Earth except that the liquid that fills its lakes and oceans, while indistinguishable from Earthly water in all ordinary circumstances, is not H20 but some other substance with a different chemical composition -call it XYZ. Going by whatever criteria are relevant to such matters, water and twin water are distinct kinds of substance, even though a chemically ignorant person would be unable to tell them apart. Now, widespread intuition appears to have it that, whereas Oscar's tokens of 'water' apply exclusively to H20, Toscar's tokens of 'water' apply exclusively to XYZ. Widespread intuition appears to have it, in other words, that Oscar's and Toscar's 'water' tokens have distinct extensions. If this intuition is sustained, then that implies either that their 'water' concepts are not individuated individualistically or that they are not individuated in terms of their referents. For Oscar and Toscar are molecular and functional duplicates of each other: they are alike in all internal respects (up to intentional description). Yet the referents of their concepts differ. Hence, either those concepts don't determine what they refer to in some context-independent way (they are not individuated in terms of their referents) or 2In this paper, I will be restricting myself to externalist theses that are motivated by Putnamian Twin Earth experiments concerning natural kind concepts. In particular, I want to put aside for present purposes externalist theses that are motivated by the influential Burge-style thought experiments involving deference to the usage of linguistic communities. I believe that an argument parallel to the one given in this paper can be mounted for those sorts of externalism as well, but will not argue for this here. 3By the schema 'x individuates y', I just mean that if the value of 'x' had been different, the value of 'y' would have been different, too. By itself, this doesn't tell us anything about what the value of 'y' is for any particular value of 'x'. More on this below. This content downloaded from 207.46.13.51 on Mon, 20 Jun 2016 05:55:35 UTC All use subject to http://about.jstor.org/terms 18. WHAT THE EXTERNALIST CAN KNOW A PRIORI they do determine what they refer to and so are not individuated individualistically. It is worth emphasizing that a Twin Earth experiment by itself does not get you all the way to an externalism about concepts; it only gets you as far as this disjunction. It is possible to respond to the experiment, and to the intuitions it generates, by opting for the individualistic disjunct and abandoning the idea that concepts are individuated in terms of their referents. That is the response favored by so-called 'narrow content' theorists. To get an argument for concept externalism you need not only Twin Earth intuitions, you also need to insist that any notion of mental content deserving of the name has to be individuated in terms of its truth conditions, has to determine the conditions for its truth or satisfaction in some context-independent way. Given this further assumption, there is then no option but to say that Earthly and Twin Earthly tokens of 'water' express distinct concepts -water in the case of the former, and let us say, twater in the case of the latter. Let us make explicit, then, the various presuppositions involved in using the TE thought experiment as a basis for concept externalism. First, and least controversially, water and twater have to be thought of as distinct substances, distinct natural kinds; otherwise, it won't be true that Oscar's word 'water' and Toscar's word 'water' have distinct extensions and referents. Second, the word 'water' -whether on Earth or on Twin Earthmust be thought of as aiming to express a natural kind concept; otherwise, the fact that water and twater are distinct natural kinds will not be semantically relevant. Third, Oscar and Toscar have to be thought of as chemically indifferent, as having no views about the chemical composition of the liquid kinds around them; otherwise, they won't end up as functional duplicates of each other in the way that the experiment requires. Fourth, the concepts expressed by the Earthly and Twearthly tokens of 'water' have to be thought of as atomic concepts, not compound concepts that are compositionally built up out of other concepts in well-defined ways. For example, the experiment presupposes that water can't be thought of as capable of being defined as: A tasteless, odorless liquid that flows in the rivers and faucets. For if it were a compositional concept of that sort, its extension would be determined by the extension of its ingredient parts. Hence, a conclusion to the effect that water and twater have different extensions would have to proceed differently than it does in Putnam's original experiment, by showing that one of the ingredients of water -the concept expressed by 'liquid', for examplehas a different extension from that expressed by its Twin counterpart. Finally, and as I have recently 201 This content downloaded from 207.46.13.51 on Mon, 20 Jun 2016 05:55:35 UTC All use subject to http://about.jstor.org/terms 202 PAUL A. BOGHOSSIAN noted, concepts must be thought of as individuated in terms of their referents.