Tuesday, 3 April 2012

Brains in vats

'Do you know? But do you REALLY know?'
Descartes invites us to imagine a scenario where everything we have ever experienced, and continue to experience, is a simulation, controlled by an evil demon with an aim solely to deceive us. More recently, philosophers have spoken of ‘brains in vats’ - imagine that we are actually brains floating in vats, in the lab of an evil scientist who is feeding us thoughts and experiences.

Both these possibilities entail that the external world (i.e. what we generally take to be the world around us) is not real, and that our entire perspective on life is in fact a delusion. I say ‘possibilities’ because, though it may seem unlikely, there is nothing in our experience that shows these scenarios to be false. If we were all were brains in vats, then our world would look no different to how it would if we really existed in the real physical world.
We may scoff at the thought of taking seriously these possibilities, and this is an understandable response - after all, let’s be honest, we’re probably not actually brains in vats. But the fact that such a scenario is possible raises famous and much-repeated philosophical problems about knowledge, and our ability to know what really is the case. If I asked you, ‘do you know that the world around you is real?’, then you would undoubtedly reply ‘yes, of course.’ However, it seems plausible that in order to really know that the world is real, we must first rule out the possibility that we are actually brains-in-vats. And since, goes the argument, we have no way of ruling this possibility out for definite, we have no way of knowing that the world around us is real! The fact that the possibility seems unlikely is not enough to conclusively rule it out.

The so-called ‘problem of scepticism’ is a problem about knowledge of the world, not the existence of the world itself. There is probably no mad scientist. Let’s take for granted that the world is most likely real - this is uncontroversial. However, even if we do this, the fact that we cannot properly rule out the possibility that we are brains-in-vats seems to threaten our knowledge of the world. We WANT to claim that we know the things we generally take ourselves to know...but, the problem of scepticism suggests that we cannot claim this. And so, our knowledge of everything falls away.


  1. One cannot claim knowledge of an aspect of reality which cannot be tested. Are we living in a computer simulation, which is itself contained in an external reality that we cannot interact with? Who cares. We cannot interact with that reality - we cannot test this claim, so it is a non-issue, not worth considering. Does there exist a God - an entity whose very definition ensures that no experiment can be devised to test for its existence? Who cares. We cannot verify these propositions, so why discuss them.

    This is summarised by Newton:

    "For whatever is not deduced from the phenomena must be called a hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy."


  2. But you can't verify that there is an external world either, since whatever experiment is done, the results will be consistent BOTH with an external world existing AND the brain-in-vat scenario being true. Experience does not favour one over the other.

  3. Reminds me of a comment in an Examiner's Report: "Candidates were as ever fond of the conclusion that though induction cannot be justified, it works in practice — a pragmatic contradiction (‘p and I’m not justified in asserting that p’)."

  4. I didn't say that we're not justified in asserting that P. The point is about knowledge, and whether we are in a position to know that there is an external world. The problem is that we are not, since sceptical scenarios (brains in vats, etc) remain possible.

  5. It is not morally wrong to kick a dog.



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