Stein asked:

Reminiscent of BIV…

I dreamt that only I am a brain in a vat and that I was chosen (due to some action of mine or thinking (of mine), perhaps, or perhaps only randomly).

Now, when I reflect on this, I cannot really say that my dream was just a dream, or that I dreamt at all. Perhaps I hit my head and am unconscious or whatever…

So, either I am a brain in a vat (perhaps in a museum for others to see and inspect) or I am not.

A very depressing thought. It’s like saying, either life has meaning or it has not.

What is the correct way to respond to this, to untangle the entangled or remove the nonsensical (to use Wittgensteinian Words). I mean, is the only option not to think about it, or can you be sceptical, where sceptical means that for all propositions p, we cannot know p (or not-p, for if you knew not-p, you would know the truth value of p), or… argh :-)

What is a proper philosophical answer to this problem, how can I easy my mind :-)

Answer by Geoffrey Klempner

You said you dreamt you were a brain in a vat. What is the experience of ‘being a brain in a vat’? The point of the BIV hypothesis is that it is impossible to tell whether you are a brain in a vat or not!

Well, suppose Morpheus comes to your front door and tells you, ‘Hey, guess what, Stein, did you know you’re really a brain in a vat?’ What has he got to do to convince you? How would you go about tricking someone into thinking they are a brain in a vat? Wouldn’t they have to be a bit gullible? (Maybe, maybe not.)

In the Philosophical Investigations, in response to the question, ‘Are you not shutting your eyes to doubt?’ Wittgenstein replies, ‘They are shut’ (PI II, p.224). The point being that doubt, like any other propositional attitude requires reasons. You doubt whether you really have a physical body because… what? simply because you can imagine that you might be a brain in a vat? (Imagining ‘being a brain in a vat’ is harder, for the reason I gave, that by hypothesis your experiences are the same either way, whether you are a BIV or not.)

There are persons who doubt, purely on the basis of things they imagine, and for no other reason at all. These doubts can be tragic or comic, depending on the circumstances. But such doubts are irrational. In the normal course of events, your eyes are shut to that kind of doubt. It doesn’t arise. That’s a pretty strong argument against global inductive scepticism, in my view.

However, the situation would be vastly different if you and I saw on the TV News that a successful BIV experiment had been carried out. More so, if body donation became feasible and there were unscrupulous operators around, kidnapping people and putting the victims’ brains in vats. Whoah!

So… do you and I know that we are not BIVs? If doubt on the question is irrational (barring the TV news announcement) then surely our belief that we are not BIVs counts as knowledge?

This is a trickier question because of contextual considerations. (I’m thinking of David Lewis’s contextual view of knowledge, see my Answer to Demetreus.) Normally, one wouldn’t talk of ‘knowing’ that P when the question whether P or not P doesn’t arise. On the other hand, if circumstances came about where it was necessary to reassure someone that you are not a BIV (say, in a telephone conversation, in the world of our imaginary TV News announcement) you might reasonably say, ‘Look, I know I’m not a BIV because I’ve taken precautions against body-snatching kidnappers!’

You could still be wrong…