Putnam, Brains in Vats, and Arguments for Scepticism

Abstract

Reason Truth and History Hilary Putnam advanced an argument to the conclusion that we are not brains in a vat which has been subjected to a good deal of criticism (Putnam, 1981). Putnam's argument has provoked a response that I think it is fair to label the standard response. The standard response is compelling. However, I aim to show that there is more to Putnam's argument than it allows. First, what is Putnam's argument concerning brains in vats, and who is it directed against? Putnam's target is the metaphysical realist. According to Putnam the metaphysical realist is committed to holding that most of what we believe could have been false. Suppose that we had been brains in a vat stimulated to hold predominantly beliefs on the basis of having non veridical experiences indiscernible from our actual experiences. that case, most of the beliefs we actually hold would have been false. So, if we could have been brains in vats of the kind described most of our actual beliefs could have been false. Hence, showing that we could not have been brains in vats defeats one reason for agreeing with the metaphysical realist that most of our beliefs could have been false. Throughout the ensuing discussion I will use in the following way. A BIV is a brain in a vat inhabiting a world which does not contain trees, houses, cats, buildings, and most of the objects we suppose to exist. Nevertheless, a BIV has experiences which ensure that what it is like to be that BIV throughout its life is just what it is like to be someone experiencing in the normal way the world we take ourselves to inhabit. Putnam makes it clear that when he refers to a brain in a vat he has in mind a BIV. He offers the following summary statement of his argument to the conclusion that we could not have been BIVs. In short, if we are brains in a vat, then 'We are brains in a vat' is false. So it is necessarily false (1981, p. 15). It seems fair to reformulate the premise of Putnam's argument as: