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Can you know you are not a brain in a vat?


To: Alistair L.
From: Geoffrey Klempner
Subject: Can you know you are not a brain in a vat?
Date: 22nd July 2009 10:48

Dear Alistair,

Thank you for your email of 15 July with your essay for the University of London Epistemology module, in response to the question, 'Can you know that 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.'

Thanks also for letting me know the result of your Logic paper. You did well. As you probably know, I am against the whole idea of giving marks for essays and will only do so when a student specifically requests it. The problem is, of course, that the entire university system depends on marking and could not exist without it. But Pathways can, and does.

In enjoyed your essay on the epistemology of the brain in a vat scenario, although (as you probably would expect) in terms of the requirements for the Epistemology paper, much of the discussion in the first part of your essay can be dispensed with. The point about the unrealistic nature of the BIV scenarios, as described, is worth making. Daniel Dennett in one academic philosopher who has expressed similar doubts (somewhere in 'Consciousness Explained'). However, you can make that point in one paragraph, and then get on with (what the examiners will see as ) the 'meat' of the question.

I will make one point in response: The BIV scenario is unrealistic, indeed unrealizable in any possible world consistent with the laws of physics (so far as we can determine, on very solid evidence). However, philosophers should always be sensitive to the 'overlooked possibility'. There are many possibilities that one has never considered or thought of. One of these might be a realistic substitute for the BIV scenario, where the various semantic and epistemological arguments apply with full force. I can't tell you what it is (by hypothesis). However, that suffices to make the investigation of the logic of the BIV scenario worth while, in my view.

The focus of the debate is knowledge. Putnam's semantic arguments are to some extent a distraction because they leave the concept of knowledge unexamined. The whole point of the BIV scenario is (or should be) to examine it. Nozick's approach at least involves important claims about the nature of knowledge (the theory of 'tracking') but they still the root question unresolved, namely the point of having a concept of knowledge in the first place.

You offer a response to Putnam. I don't think it works. You say, 'The argument that should be challenged is:

'1. I know that I am sitting in a chair therefore I know that I am not a brain+ in a vat+

'2. I do not know that I am not a brain+ in a vat+, implying

'3. I do not know I am sitting in a chair

'Where the + indicates reference to entities in the inaccessible super-reality.'

Putnam's reply is going to be, that meaning and reference can't be achieved by magic. You think you've secured reference to brain+s and vat+s just by adding the qualification 'in the inaccessible super-reality', just as one might say, 'There are humanoids somewhere in Andromeda'. That is to say, we are talking about the same thing that you or I would understand as a 'humanoid' were we to encounter one (a non-human creature resembling a human being in behaviour and outward appearance) only a lot further away. But inaccessible super-reality isn't just a lot further away. It isn't anywhere in 'reality' or 'the world', in the only sense which these terms can have.

(You can always assert, like some old-time metaphysician, that reality or the world we know is only appearance not Reality. But that requires an argument; such as Parmenides' argument for 'It is' or Bradley's attack on relations.)

My reply to Putnam would be that you can have everything you want the BIV scenario to be, without having to address the question of how the meanings of the terms in the BIV's 'language' are determined, by simply converting the argument into an argument about 'possible experience'.

All sorts of experiences are possible. In the Matrix, Neo wakes up in a vat, floating in a gooey liquid with plastic pipes attached to his body. That's a possible experience. You don't have to believe what you see. The point, however, is that there are possible experiences which would leave unable to decide what you believe. The longer the 'waking up' period lasts, the more likely you are to accept that this is 'reality'. That's just a pragmatic test.

So my version of the argument would go:

1. I know that I am sitting in a chair therefore I know that at no time in the future will I be in a position to say that I now realize I was not then sitting in a chair. (Insert your 'possible experience' scenario here.)

2. I do not know that there is no time in the future when I will be in a position to say that I now realize I was not then sitting in a chair.

3. I do not know I am sitting in a chair.

If I was writing this essay, I would try to use this argument to explore the 'softness' (which is not the same as vagueness) of our concept of knowledge, exploring why scepticism cannot be defeated by any knock down argument but at the same time, why there is no need to defeat the sceptic. (And I don't accept that to say that knowledge is a soft concept is to be kind of sceptic.)

So, yes, like you I find a lot of the fine-grained discussions in epistemology somewhat over-rarified.

All the best,