Professor Putnam on brains in vats

Abstract

In 'The Philosopher's Nightmare' (Proceedings of the Aristotelian Society, 1967) I envisage Ludwig, a brain in a vat, being given a systematic series of hallucinations from the moment of his birth by Dr. Smythson, the neuro-surgeon responsible for his unfortunate plight. In Chapter I (entitled 'Brains in Vats') of Reason, Truth and History Professor Putnam has held that the hypothesis that everyone is, like Lud? wig, a brain in a vat, though physically possible, is conceptually impos? sible. Though brains in vats will be able to combine words with other words to form correct English sentences, they will not be able to correlate the words in these sentences with actual things, because they have never come across any. Hence they will not know what these words mean. Since they have seen only image brains and image vats, their word 'brain' will mean 'image brain', and their word 'vat' will mean 'image vat'. But they are not image brains in image vats; they are real brains in real vats. So what they all believe (that they are image brains in image vats) will be false. Hence, in a world in which everyone is a brain in a vat, it will be false that anyone is a brain in a vat. Hence (since (p => -p) => -p) it will be false that there are any brains in vats. There are two things wrong with this argument. First, it contains the same fallacy as the argument 'In a world in which by 'round' everyone meant flat, it would be false that the world is round. Fairly obviously, however, the world would be round whatever people meant by 'round'. Men's (or even brains') use of words cannot have effects of such cosmic proportions. If everyone by 'round' meant flat then what they would be using the words 'The earth is round' to say would be false, but they would be using these words to express the fact that the earth is flat, which it is not, not the fact that it is round. What we mean by the words 'The earth is round' would still be true, though, in a world in which people used this word to mean what we mean by 'flat' now, this truth could not be ex? pressed in the words 'The earth is round'. (Perhaps it would be expressed in the words 'The earth is flat'). The roundness of the earth is not in any