Ray asked:

Are you a brain in a vat? Does it matter?

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Am I a brain in a vat? Impossible to prove either way. Does it matter? Depends on how you mean the
question. In terms of my day-to-day doings, no, it doesn't matter. How could it, if I don't actually know
one way or the other? I would still behave in the same way and would perceive everything around me
in the same way.

My year 11 students have been looking at this question and found the discussion in Stephen Law's
Philosophy Gyminteresting. The film 'The Matrix' also takes this as its basic premiss.

Lyn Renwood

In 'The Matrix' the question is raised whether it 'matters' whether I am a brain in a vat (or, rather, a
body in a vat) but the film doesn't give the answer. It asks, 'Would you take the red pill or the blue
pill'? Take the red pill, wake up to reality and fight for the revolution, or take the blue pill and forget
that you were ever asked to make the decision.

Would I still bother to post these questions and answers, if I suspected that I was a body in a vat?
Yes, because the activity would still be what I believe it to be — human subjects conversing about
philosophy. Would I still bother to keep fit? Yes, because that has important practical consequences
for me in my virtual world.

But if I had the choice to take the red pill and discover the awful truth or take the blue pill and continue
living a contented lie? In my answer to Dian in the early days of Ask a Philosopher (Answers 5 23) I
wrote "I would take the red pill, without hesitation. As a philosopher, I have to say that." Why?
Because the philosopher's ultimate concern is with 'the truth' — at any price.

However, as Ray's question shows, there is a thirdpossible alternative. Take the red pill, discover
how bad things really are (a world turned into a post-apocalyptic hell) then ask to be put back in the
vat but NOT have your memories erased.

Geoffrey Klempner

I thought it would be worth mentioning an alternative response to this question because it is rarely
represented on these answer pages and this gives the impression that philosophers are all in
agreement over the impossibility of knowing whether we are brains in vats. This alternative response
comes from the tradition in philosophy which questions the assumption that fallible knowledge is
impossible.

The first response to this question would be to look at the context in which it is asked. For instance a
philosophy student may ask the teacher 'am I a brain in a vat?' to which the answer could very
plausibly be 'No' (given that you are unlikely to have a brain in a vat asking such questions in your
philosophy class). On the other hand you could say along with the other philosophers on this list 'I
don't know'. Although I think that it would strike most people as a decidedly odd thing to say. In the
same way if someone asked you whether you were awake or not and you said 'I don't know' it would
cause some puzzlement.

The philosopher who holds that they don't know whether someone in their class is a brain in a vat or
not is assuming that they cannot know what it is possible for them to be mistaken about.

They are relying on their experiences being a reliable guide to what exists and yet they are aware that
it is possible for their experiences to be systematically deceiving them. On this view I cannot know
anything because knowledge has to be infallible.

The alternative view to the above is to say I can know things without being infallible and to point to
how the term 'know' is actually used in everyday life (where claims do not require infallibility).
According to this view the source of puzzlement is due to the philosopher taking terms out of their
ordinary context where they have a use and placing them in another context where they cease to
function.

There is no easy way to settle this question over what you can know. However as an indicator of
which position to adopt you could try the following test to see what your intuitions tell you is the more
plausible.

Do your intuitions tell you that you can tell the difference between a brain in a vat and a person?

or,

Do your intuitions tell you that you cannot know something unless it is impossible for you to be
mistaken about it?

As to the second part of the question 'does it matter' — Well ask yourself whether you would trade
places with a brain in a vat. If your answer is no then ask what reasons you would not trade places
with a brain in a vat. This will indicate what sort of factors 'matter'.

Julian Bennett