1 Putnam, Hilary Reason, Truth, and History (Cambridge: Cambridge University Press 1981CrossRefGoogle Scholar). References to this volume henceforth appear parenthetically. Emphasis in quoted passages appears in the original.

… [T]he fact that [brains in a vat] are conscious and intelligent does not mean that their words refer to what our words refer. … (T)here is no connection between the word “tree” as used by these brains and actual trees. They would still use the word “tree” just as they do, think just the thoughts they do, have just the images they have, even if there were no actual trees. Their images, words, etc., are qualitatively identical with images, words, etc., which do represent trees in our world; but … qualitative similarity to something which represents an object … does not make a thing a representation all by itself. In short, the brains in a vat are not thinking about real trees when they think “there is a tree in front of me” because there is nothing by virtue of which their thought “tree” represents actual trees. (12f.)

2 We may rule out the possibility that appropriate representational connections might be established through the computer by imagining that the automatic machinery that feeds impulses to the envatted brain came ‘into existence by some kind of cosmic chance or coincidence’ (12).

3 Mark Overvold has pointed out to me that Putnam's claim that the brain in the vat hypothesis is incoherent renders the use of premise (2) dubious. Can one entertain an incoherent thought?

4 See Earl Conee's review of Reason, Truth, and History, forthcoming in Noûs; Jane Mcintyre, ‘Putnam's Brains,’ Analysis 44 (1984), 59-61; and James Stephens and Lilly-Marlene Russow, ‘Brains in Vats and the Internalist Perspective, ‘Australasian Journal of Philosophy 63 (1985), 205-12.

5 There may be other, independent, nontranscendental grounds for regarding this hypothesis as unintelligible or in some other way defective. These will not be discussed here.

6 Wittgenstein, L. Tractatus Logico-Philosophicus, trans. Pears, D.F. and McGuinness, B.F. (London: Routledge and Kegan Paul 1961Google Scholar), sec. 5.6

7 Donald Davidson has argued that talk about ‘perspectives’ and ‘points of view’ seems to require that there be something on which there can be perspectives and points of view. See ‘The Very Idea of a Conceptual Scheme,’ in his Inquiries into truth and Interpretation (Oxford: Oxford University Press 1984). See also Heil, J. Perception and Cognition (Berkeley, Los Angeles, and London: University of California Press 1983), 108-18.Google Scholar

8 Perhaps one can distinguish realism (or one form of realism) from externalism in the following manner. According to the realist, the world might be a certain (unspecified) way, even though, were it that way, one would be barred from having thoughts about it, more particularly, thoughts that it was that way. On this view, how the world is is not determined by how one thinks it is. Externalism, in contrast, is a doctrine about sentences. According to the externalist, sentences may be true even though they are (in the sense discussed above) inaccessible. It is far from clear that realism requires externalism.

9 A version of the present paper was presented at the American Philosophical Association meetings, Washington, D.C., December 1985. The commentator was C. B. Martin. I benefited from his comments as well as those of two anonymous referees for this Journal. Barry Brown deserves much of the credit for the formulation of the arguments discussed here, although he undoubtedly would disagree with a good deal that I have said about them. In any case he and Mark Overvold are responsible for whatever I have managed to get right.