To: Mark S.
From: Geoffrey Klempner
Subject: Can you know you are not a brain in a vat?
Date: 7th March 2008 12:48

Dear Mark,

Thank you for your University of London BA Epistemology essay in response to the question, 'Can you know you are not a brain in a vat? If you answer Yes, explain how you can know this. If you answer No, spell out the consequences of your answer for ordinary pieces of knowledge.'

In answer to the first part of the question, you reject G.E. Moore's anti-sceptical argument that he just *knows* that he has two hands. Your response to Putnam's argument that according to a causal theory of reference, a brain in a vat cannot have a concept of a vat, you argue that this state of affairs would be tantamount to a more radical scepticism according to which not only could we not know anything about an external world, we could not *mean* anything by our statements referring to an external world. It follows that I cannot know that I am not a brain in a vat.

As you will have gathered from my remarks in response to your previous Epistemology essay, I am in agreement with you on both these points.

As it is my job to pick holes and find angles that you haven't considered, it did occur to me that the question, 'Can you know you are not a brain in a vat?' can be understood in two different senses. You have taken it in the standard, sceptical sense as, given my situation here and now, is all I have experienced sufficient to rule out the hypothesis that I am a brain in a vat? The answer to that question is, No.

However, there is another sense of 'Can you know that you are not a brain in a vat?' which means, 'Can we imagine circumstances in which it would be possible to know that you are a brain in a vat?' Imagine a scenario where some brains are envatted while others are not. Brains are routinely taken out of bodies and put in vats, or taken out of vats and put back in their bodies. By very careful attention to certain anomalies in your experience (e.g. repeating cats, rules being 'bent', as in the Matrix films) it might possible to tell with a high degree of accuracy whether you are currently envatted or not. No doubt Putnam would have something to say about this, but when I said above that I agreed with your dialectical response to Putnam I didn't mean to imply that I accepted his view of the causal theory of reference and its consequences. (This is in fact part of an argument I would mount against Putnam.)

In your answer to the second part of the question, you consider Nozick's account of truth tracking as an explanation of why the principle of closure fails, and also Contextualism which accepts the principle of closure but claims that there are different standards of 'knowledge' in different circumstances.

In both cases, your objection hinges on the intuition that knowledge is something absolute, an all-or-nothing concept. If I don't know that I am not a brain in a vat, then the knowledge that I have two hands, or that I am writing an email to you, isn't really *knowledge*, even if it is a belief which, say, is sufficiently reliable for practical purposes. 'I have two hands' can't be something which is 'true when out shopping, but false when discussing radical scepticism'.

In response to your first point, it seems that the anti-sceptic does have some room here to mount a defence. You say that you 'know' what you mean by 'knowledge', but how do you know this? Isn't the very least that follows, from your statement, 'I don't know that I am writing this essay', that there is room for *doubt* whether or not you are writing this essay? If there is no room for doubt, how can you not know? But what *is* doubt? To doubt that P, it is not sufficient to consider the logical possibility that not-P. In addition, there has to be something I can do, some way I can act, in order to make this *my* doubt. But that is something I cannot do. To say, 'I doubt', is not yet to doubt.

(Hence, Wittgenstein's cryptic response to the sceptic: 'Aren't you shutting your eyes to doubt?' 'My eyes are shut.')

In response to your second point, the question isn't about truth or falsity but knowledge. Your response to the sceptic is not, 'Even if I am in fact a brain in a vat, I still know I have two hands for the purposes of going out shopping.' That would be to relativize truth to 'truth in a world' (truth relative to the vat world, versus truth relative to the actual non-vat world). The sceptic is saying, 'Even if, in fact, I am not a brain in a vat, I still don't know this because if I was a brain in a vat I would think I was not a brain in a vat.' The contextualist response is to say that, if indeed I am not a brain in a vat then my belief that I have two hands is sufficient to meet the standards of knowledge in the contexts in which I normally use this term.

I liked your final parting short about Hume and the game of backgammon: 'The truth of a scientist's argument that being an ideal body weight is healthier than being overweight would not be refuted by his obesity, and the truth of his argument that it was healthier not to smoke than to smoke would not be refuted by his addiction to tobacco.'

In defence of Hume, I would argue that the point may be seen as being about the relation between knowledge and action (as above). Hume's project is to construct a 'theory of human nature' where the things we believe are founded, not on reason but on nature. In this 'context', scepticism is not a rejection of the possibility of knowledge but rather rejection of a false 'rationalist' account of the nature of human knowledge.

All the best,

Geoffrey