By the same argument, ‘vat’ refers to vats in the image in vat-English, or something related (electronic impulses or program features), but certainly not to real vats, since the use of ‘vat’ in vat-English has no causal connection to real vats (apart from the connection that the brains in a vat wouldn’t be able to use the word ‘vat’, if it were not for the presence of one particular vat — the vat they are in; but this connection obtains between the use of every word in vat-English and that one particular vat; it is not a special connection between the use of the particular word ‘vat’ and vats). Similarly, ‘nutrient fluid’ refers to a liquid in the image in vat-English, or something related (electronic impulses or program features). It follows that if their ‘possible world’ is really the actual one, and we are really the brains in a vat, then what we now mean by ‘we are brains in a vat’ is that we are brains in a vat in the image or something of that kind (if we mean anything at all). But part of the hypothesis that we are brains in a vat is that we aren’t brains in a vat in the image (i.e. what we are ‘hallucinating’ isn’t that we are brains in a vat). So, if we are brains in a vat, then the sentence ‘We are brains in a vat’ says something false (if it says anything). In short, if we are brains in a vat, then ‘We are brains in a vat’ is false. So it is (necessarily) false. Hilary Putnam, ‘Brains in a vat,’ Reason, Truth and History, (Cambridge 1981), 14-15.
i) Even though this is a famous science fiction scenario, in the future it may be a realistic scenario:
ii) As an anti-skeptical argument, I don't think Putnam's argument succeeds. The argument, if successful, is counterproductive. It would mean that even if you are a brain in a vat, you won't be in a position to recognize your predicament because you lack the language and concepts to entertain that possibility. But surely that's the non plus ultra of global skepticism.
iii) However, I don't think his argument works at another level. It's true that to recognize your predicament as a brain in a vat, you need an external frame of reference. However, the lab could have a camera trained on the transparent vat, with tubes and wires. That information could be fed into the brain so that a disembodied brain could see itself in the vat, with the neurointerface.
iv) From a Christian standpoint, the source of consciousness is the soul, not the brain. And even if (ex hypothesi) brains were harvested in the womb and deposited in the vat, spending their entire lives in the vat, God could reveal himself directly to the embrained but disembodied soul–just as God intervenes in human history. Take revelatory dreams, where God gets right inside the mind of the dreamer. If need be, God could enter the mind of the embrained but disembodied soul. Bypass the neurointerface. Make himself known from within.
I thought that through a reliabilist epistemology we can know that we are not brains in a vat.
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