Descartes’ scepticism threatens our grasp on the external world, opening up a gap between it and what we experience. The sceptical argument works by describing a ‘ringer’ for our pre-philosophical view: an alternative that we cannot distinguish from that pre-philosophical view. For all we know, it might be true. But if that is the case, then we cannot know that it is not true and thus, goes the argument, we cannot know any of the empirical facts we take ourselves to know about the external world which are incompatible with it. (Note that the ringer concerns the external world. So the resulting scepticism is limited to that. It does not, for example, appear to threaten a priori truths such as mathematical truths.)
Descartes’ particular version of the ringer has been updated both (approximately) in the film the Matrix but also, more modestly, in the idea that I might be a brain in vat, fed electrical impulses which mimic (the look and feel of) worldly experiences but are not veridical (ie. truthful). As far as I know, I might not be a person in a world but a brain in a vat. That’s the ringer.
But if this argument is to work, the ringer must be coherent. It must be an alternative for us. That is just what Hilary Putnam (male, by the way!) targets. His argument is that the idea that I might be a brain in a vat is not something I can both coherently and truthfully entertain. If I were a brain in a vat, I could not think it. If I can think it, that is because it is not true. If Putnam is right, then it is not an alternative I need to rule out and thus external world scepticism does not get off the ground.
Is such a wonderful argument possible?
Essential reading
Putnam, H (1981) Reason, Truth and History, Cambridge University Press chapter 1 ‘Brains in a vat’ pp1-21. You can find a copy here.
Further reading
Stanford Encyclopaedia entry on brains in a vat which is written by Brueckner (see below).
The following are also in a folder 'Brain in a vat' on WebCT if you wish to dig deeper. They are heavy going. One question to ask yourself when looking at the original argument, the Stanford entry or any of the additional texts, is what effect Putnam's claims about how reference is fixed relate to a subject's self-knowledge of their own mental states (for the moment: whether or not they are true or false).
Brueckner, A. (1986), Brains in a Vat, Journal of Philosophy 83 (this is lengthy and complex; start with the stanford entry first)
Brueckner, A. (1991), If I Am a Brain in a Vat, Then I Am Not a Brain in a Vat, Mind 101 (this is a reply to Dell'Uti but is in fact short and free standing).
Dell'Utri, M. (1990), Choosing Conceptions of Realism: the Case of the Brains in a Vat, Mind 99
Forbes, G. (1995) Realism and Skepticism: Brains in a Vat Revisited The Journal of Philosophy, 92: 205-222 (this connects to broader themes in Putnam's thinking about realism)
Reflections on this session.