Tuesday, 20 January 2015

On 'If you're a brain in a vat then you don't have hands'

This is a bit rough and rambling. A much more focused rewritten version, taking into account more of the relevant literature (especially pieces by Bouwsma and Chalmers), is here.

Much ink has been spilled on skeptical arguments like the following:
  1. If you're a brain in a vat then you don't have hands
  2. You don't know that you're not a brain in a vat
  3. Therefore you don't know that you have hands
There are many variations on this sort of argument, and many issues have been raised about it, for example the issues of the closure of knowledge under implication, and the closure of knowledge under known implication.

I have long felt that there is something very dubious about the first premise in the above formulation (and the analogous premises in the variations). I suspect that coming to terms with this would involve throwing a spanner in the works of some of our ways of thinking about how language functions (we being analytic philosophers, broadly speaking). Not necessarily at the level of explicit commitments, either. And perhaps that is part of the reason why this premise has not been questioned, in anything like the way I want to question it, much in the literature1; it seems very difficult.

In this essay I want to begin to explore this issue. It is a pretty large and confusing issue, and this is only meant to be a beginning, so I will try to be fairly non-technical and to avoid bringing in any very particular overarching theoretical framework, out of fear that if I did so the issue or important aspects of it would get lost.

I will suggest that (1) is not true – or at least, that it isn't true on its most natural readings. If I am right, then we may have a way of avoiding the repugnant conclusions of skeptical arguments like the above, without having to show that we do somehow know that we are not brains in vats. This seems attractive to me – it does intuitively seem to me that I do know that I have hands and that I do not know that I'm not a BIV. Or perhaps better, and from a broadly Lewisian contextualist perspective on knowledge-ascriptions (a perspective I find independently attractive)2, it seems to me that there are levels of strictness – or sets of relevant alternatives – on which 'I know I have hands' comes out true while 'I know I'm not a BIV' comes out false.

So, one thing which may come out of this discussion is a way of diffusing a large class of skeptical arguments. But my motivation isn't primarily epistemological – isn't to vouchsafe certain bits of presumed knowledge. For my part, I don't think that sort of philosophical anxiety about whether we really know such-and-such should always be indulged and attempts made to alleviate it by the straightforward course of trying to come up with reasons to be reassured. It seems largely pathological to me – something which ought to be scrutinized and dissolved, as I think Wittgenstein tried to do.3

No, I'm more interested in (1) for its own sake, and for the sake of the issues which come up once we begin to question it. As we will see, these are fundamental issues in the philosophy of language – for example, the issue of what propositions are, and the issue of whether we ought to think of propositions as sorting all possibilities into two categories (one of which may be empty): those in which the proposition holds, and those in which it does not. (We will not have space to go deeply into these issues in a general way, but we will end up seeing that we have here found one good path into them.)

So much for scene-setting. To kick off the investigation, let us note that (1) is generally supposed to be accepted readily, as though it were obvious. It just appears in skeptical arguments as a premise, which we're meant (by the skeptic) to accept without argument. Once you start scrutinizing it as I have done, this quickly begins to seem very odd and confusing. So, to try to avoid being hampered by such confusion when we do scrutinize it, let us first ask the question: why might (1) seem true?

Silly as it sounds – silly as it is – the answer appears to be something like: when (1) strikes us as true, we are as it were picturing a brain sitting in a vat, and observing that there are no hands in that picture. Or we are picturing a brain sitting in a vat, and a mad scientist tending it, and noticing a striking contrast between the two figures – the scientist-figure has a body and hands, whereas the other figure is just an organ (in a vat). Something along those lines.

And here is a good place to consider and put aside one particular line of attack on (1). It is a comically literal-minded objection. I did not think of it myself, but found it when I was searching the literature for previous attempts at calling propositions like (1) into question. (And this is all I found.) Roush (2010) argues that it is not true that if you're a brain in a vat then you don't have hands, on the grounds that you might be a brain in a vat with hands just stuck on (!) – that is, where there are attached hands in the environment which contains the brain and the vat, not the environment simulated for the brain. Maybe the hands are just stuck on with glue and dangle there, or maybe they are delicately connected up neurologically with the brain, making for a queer straddling of two “worlds” (or environments, or levels of reality) on the part of the BIV.

There is something very frustrating about this objection. It is frustrating, I think, because if you just accepted this objection, deciding on its basis that (1) is false, and then walked away, you would have bypassed all the deep issues in the philosophy of language which we can dig up by scrutinizing (1), thus losing a valuable opportunity.

Calling the objection into question – scrutinizing it – may lead somewhere, however. For instance, we may ask whether a BIV with the envisaged appendages really counts as 'having hands', or whether this is really the best candidate meaning for 'having hands' in connection with a BIV. And here we begin to get the sense of an abyss, this sense of unforeseen ambiguity or indeterminacy, and the sense that this sort of thing, since it's not very clear how we should think about it, has ominous implications for how we think philosophically about language.

These spectres raised just now are at the heart of what I am concerned with here, but they come up with (1) itself anyway, quite apart from the literal-minded objection we have just looked at. So, what I propose is that we put this objection to one side, go back to what we said about why (1) might seem plausible, and proceed from there.

(If you think the objection does show (1) to be simply false, you may be more comfortable with the ensuing discussion if you exchange (1) for something like 'If you're a brain in a vat without appendages as envisaged in Roush (2010), then you don't have hands'. But really, it hardly matters, since the point of this discussion is not really to determine the truth-value of (1). Indeed, the idea that (1) as used in skeptical arguments has a definite meaning, and a definite truth-value, may not survive scrutiny. And our idea of what a 'definite meaning' is, and of what role the notion of definiteness should play in thinking about meaning, may have to be altered too.)

So, we picture a BIV and there are no hands in the picture. And we picture a scientist tending the BIV and see a contrast between the figure of the scientist and the BIV-figure. And with this in mind, we might be tempted to say 'The BIV doesn't have hands and the scientist does'.

But consider a different situation, in which we have two BIVs. It doesn't matter whether or not they are plugged into the same simulation. What does matter is that, in their lives in their simulation(s), one of them is an anatomically normal human, while the other has been in an accident and lost their hands. Mightn't we, if this was the first case we had considered, be tempted to say 'One BIV has hands, the other does not'? And if we would be right in so saying, then we would be wrong to say (without shifting the meanings of relevant terms) that if you're a brain in a vat you don't have hands; the first BIV would then be a counterexample to (1).

Here it might be objected that it would not be correct to say, unqualifiedly, 'One BIV has hands, the other does not' – rather, one would, to be both right and completely explicit, have to say something like 'One BIV has hands in its simulated environment, the other does not'.

Suppose we go along with the objection. We can still ask about things the BIVs may say, in their simulations. And we could reason as follows: Surely, if the first BIV says, in the simulation, 'I have hands', they are, in the simulation, saying something true. And surely if they say, in the simulation, 'I am a BIV', they are, in the simulation, saying something true (even if they could never know it to be true). And thus, if they said 'If you're a brain in a vat then you don't have hands', they would be saying something false – something to which their very case is a counterexample. And if that's right, how could (1) fail to be false? How could our situation differ from the BIV in question's situation in such a way that (1) is true, whereas their utterance – in the simulation – of 'If you're a brain in a vat then you don't have hands' – is not? I can see no way. And furthermore, if there was a way, surely it would turn on us not being BIVs, not living in a simulation – and in that case, we wouldn't be able to know (1) without first knowing that we are not BIVs, and so the skeptical argument could no longer be run.

Now, the above reasoning seems natural, but of course it could be challenged. The most salient way it could be challenged would be to follow Putnam's notorious paper (1981) in saying that, when the BIV says, in their simulation, 'I am a BIV', they are saying, in their simulation, something false, contra the above reasoning.

I do not have space here to lay out Putnam's arguments in full, and to discredit them in detail, but I think it is important to realize that Putnam is completely wrong on this point, and to see why. I will now briefly try to defend this, and to say something about what was going on with Putnam for him to be led so far astray.

Putnam begins with a causal theory of reference, according to which what you're talking about when you say something is what stands in an appropriate causal relation with your utterance. He argues, from the causal theory, that since a BIV could have no causal contact with the brain they are, and the vat they are in, they could not be talking about that when they say 'I am a brain in a vat' – rather, their utterance is, according to Putnam, about 'vats-in-the-image', 'or something related (electronic impulses or program features)'. And since they, the utterers, are not vats-in-the-image, i.e. not vats belonging to their simulation, nor the relevant 'related' things, what they thus say comes out false.

There are lots of things about this we could argue with – the idea that the BIV's talk might literally refer to electronic impulses or program features seems to me very crude and objectionable, for instance – but I will confine myself to three points, the first two of which are closely related to each other.

Firstly, note that singular reference – reference to particular objects – isn't what is in question here. Putnam isn't saying that to say something which is made true by the state of some particular object O requires that we have causal connections to O itself. That, after all, would yield absurd consequences (not that that tends to stop Putnam, but ignore that; these absurd consequences aren't as cool or interesting). For example, I may say, let us suppose on a whim, 'A man will walk into the room now', and if a man immediately walks in, what I said is true, in virtue of that particular man's walking in. But of course the man need not have any causal connection with what I said. All Putnam would insist on is that, in order to be about men at all, my talk needed to have an appropriate causal connection with some man or men. Likewise, in order for a BIV to think or say they are a BIV, their thought or talk doesn't have to be causally connected with the brain they are or the vat they are in. It just has to be connected with some brain(s) and vat(s).

Secondly, why can't there be a general category marked with the word 'vat' which includes as members both “vats-in-the-image” - vats in simulations – and vats outside simulations? (Likewise for 'brain'.) I think there can. Consider things like happiness and intelligence: a BIV with a rich life is surely acquainted with these things, and causally connected with exemplars of them – and so they can have a category, for example marked 'expressions of happiness', and this category would include both things in their simulated environment and any appropriate things outside the simulation. And so Putnam's argument falls down here, by implicitly holding that the relevant reference classes – the 'brain' class and the 'vat' class – can only include things in the utterer's “world”. Once we see this is not so, we can go along with Putnam's basic causal-theoretic starting point, but maintain that there is nothing stopping them thinking they are BIVs, because they can form categories – by means of causal connections to brains and vats in their environment – which manage to include the brain they are and the vat they are in, despite those particular instances not being in their environment.

Thirdly, and stepping back a bit, note how implausible and crude Putnam's interpretation of the BIV's utterance 'I am a BIV' is; it's supposed by Putnam to assert something which to the BIV would be obviously wrong – namely, that they are brains in their environment in vats in their environment. And yet a reflective BIV might not find their utterance of it obviously wrong at all. This suggests that something has gone badly wrong. At a very general level, we may say that Putnam's problem is that he has inappropriately treated the language-game of talking about being a BIV as being just like an ordinary one about things in our environment. But it is plainly not that. Language, we might say, is here playing an entirely new trick. We may not be able to come up with a theoretical understanding of it which would satisfy Putnam, but that does not mean he gets to falsify it.

So, if I'm right about Putnam here, then the reasoning we went through just before considering him seems hard to argue with. And thus, it seems that (1) isn't true, at least on the most natural ways of understanding it. At the very least, it should certainly seem by now that (1) is not the straightforward truth it may have looked to be at first. There are serious challenges to be raised against the naïve, unreflective procedure of just (doing something like) picturing a brain in a vat, observing that there are no hands in the picture, and drawing (1) as a conclusion.

But we are in a bit of a muddle now, only halfway through the essay. A lot of arguments and worries have piled up. I want now to try to restore our energies by clearing the table and approaching the issue from the other side: why might we think (1) is false?

I have an intuitive case to make for thinking that (1) is false. It involves considering statements made in ordinary, everyday conversation, statements which intuitively seem to imply that the utterer has hands, but which intuitively seem not to imply that the utterer is not living in a simulation. For example, suppose someone asks me to help them with something and I say 'OK, one second - I'm just washing my hands'.

This statement – that I'm washing my hands – surely implies that I have hands. Furthermore, I find it very intuitive that it does not imply that I'm not living in a simulation, or that I'm not a BIV; that simply isn't at issue at all. It is completely independent of the truth of what I said.

Having hands is compatible with it not being the case that I'm not a BIV. And so, having hands is compatible with my being a BIV. And so it can't be true that if you're a BIV then you don't have hands.

The key intuition there – that my ordinary statement does not imply that I'm not living in a simulation – can perhaps be bolstered by thinking a bit about the space of scenarios in which I am living in a simulation, and seeing that it is possible to take an attitude to many of these scenarios which is quite unlike regarding them as epistemic nightmares, i.e. situations in which we're in really bad shape epistemically – where much of what we ordinarily think we know fails to even be true.

Certainly we can imagine simulation-scenarios which are epistemic nightmares. We may be BIVs whose tending scientists are engaging in all kinds of foul play, planting false memories and moving things around on us. Also diabolical would be if some or all of the apparent agents we are interacting with are not sentient, or not as fully sentient as we think. I don't so much mean that they may not be constituted the way we are, or the way we think they are – after all, multiple realizability might be the case – but rather that maybe all there is to these agents is what's required to generate our interactions with them. And in lots of cases, corners may be cut, so to speak – when we think they're off by themselves having a rich mental life, perhaps often nothing of the sort is true. But nightmarish scenarios like this are clearly a special subset of all simulation scenarios; in many of the latter, we may not be wrong about much of anything. It just might be the case that, unbeknownst to us, there is a higher level of reality “hosting” the one we inhabit, and this level may involve brains in vats.

From this point of view, we can see that there is no need to respond to the news that you're a brain in a vat by revising your belief that you have hands. Why not treat the news instead as telling you, among other things, something new about your hands (and everything else in your environment), namely that they are “hosted” at a higher level of reality, or speaking crudely, are constituted by electrical impulses or program features. (I say 'crudely' because the relation is obviously not the normal one of constitution from normal physical inquiry. Physics can be done in a simulation, too, and facts about the simulation being a simulation need not be regarded as belonging to it.)

I contend, then, that once we reflect a bit, we can see that (1) is false, at least on the most natural ways of construing it.

Why the hedge about 'most natural ways'? Well, there is one way of construing 'hands' I can think of which is not totally discontinuous with what 'hands' really means and which would make (1) come out true. Namely, a way on which hands are taken as a matter of definition to be things which exist only at the highest level of reality. (Note, in case it seems woolly or unclear, that this notion of levels of reality I've been throwing around does not precede, or exist apart from, considerations of simulations. It is a special notion for talking about these very special matters. Despite possible appearances, there's no more general story about it which could be missing or unsatisfactorily hand-waved to here.)

So there is this construal. But when we adopt it, the conclusion of the skeptical argument, that we don't know that we have hands, isn't particularly repugnant any more. And this, by the way, shows that the construal in question isn't very natural, since we do feel the conclusion as ordinarily understood to be highly repugnant. That conclusion can't be put at the end of the skeptical argument without either rendering (1) false, or keeping it true but equivocating on 'hands'.

So much for (1) and its role in the skeptical argument. I will now begin to conclude, with some more general remarks about meaning and propositions.

It seems like there's something artificial about pinning a particular resolution of these issues of 'What exactly does it take to be a hand, anyway?' on ordinary talk about hands, no matter which one we pick. Rather, something along the lines of there being no fact of the matter seems to be the case. Consider in this connection Wittgenstein's case of the disappearing chair:

§80. I say "There is a chair". What if I go up to it, meaning to fetch it, and it suddenly disappears from sight?—"So it wasn't a chair, but some kind of illusion".—But in a few moments we see it again and are able to touch it and so on.—"So the chair was there after all and its disappearance was some kind of illusion".—But suppose that after a time it disappears again—or seems to disappear. What are we to say now? Have you rules ready for such cases—rules saying whether one may use the word "chair" to include this kind of thing? But do we miss them when we use the word "chair"; and are we to say that we do not really attach any meaning to this word, because we are not equipped with rules for every possible application of it?

So, what of propositions? What of meaning? Should we say that hand-talk is somehow incomplete, failing to express determinate propositions? Well, we could say that, but this is taking the notions of a proposition and of meaning pretty far from home. And what for? Perhaps the only answer is: to preserve certain ways of thinking about how propositions work, and what they do (for example, the idea we mentioned at the outset that propositions sort all possibilities into two categories). But is that wise? Were these ways of thinking the results of investigation, or a priori requirements? (Cf. entry 107 of the Investigations.)

In any case, does the breakdown of these ways of thinking here mean they have to be chucked out entirely? No – we could think of them as offering an idealized perspective. A perspective which is robust in some areas of thinking, useless perhaps in others, and worse than useless in others again.

Now to stop and take stock. Firstly, (1) is no straightforward truth. Secondly, there's a lot more to it than there might seem to be at first glance. Thirdly, it is very arguably false on the most natural ways of understanding it. There's one somewhat natural way on which it's true, but on that one the conclusion isn't very repugnant. Finally, we have looked fleetingly at what all this might mean for the fundamentals of philosophy of language, and suggested that certain ways of thinking about language which run into trouble here are either just bad, or at best are idealizations which have some value but can easily break down and become inappropriate. And they do break down and become inappropriate very quickly once we scrutinize (1).


Lewis, D.K. (1996). Elusive knowledge. Australasian Journal of Philosophy 74 (4):549 – 567.

Putnam, H. (1981). 'Brains in a Vat', Chapter 1 of Reason, Truth, and History. Cambridge University Press.

Roush, S. (2010). Closure On Skepticism. Journal of Philosophy 107 (5):243-256.

Wittgenstein, L. (1953/2003). Philosophical Investigations: The German Text, with a Revised English Translation. Blackwell.

1. I say 'much in the literature' in case there are documents I am unaware of which question it in something like the way I have in mind; I haven't been able to find any. On the other hand, this does seem to me to be the sort of thing that a philosopher might register in passing in a document mainly about something else. I wouldn't be at all surprised therefore to find myself anticipated to some extent in that way.

2. Cf. Lewis (1996).

3. I am uneasy about this though, since running with such epistemological worries and trying to meet them straightforwardly and on their own ground has borne spectacular philosophical fruit, as it were along the way, even if the worries are ultimately never thus met. Russell's quest for certainty and his work, in service of this quest, in mathematical logic and philosophy of language, seems a spectacular example. The quest seems a sad vestige of a screwed up childhood, while the result of the quest includes spectacular advances in logic, the theory of descriptions, and long-overdue attention to Frege. This kind of alchemy seems unsettlingly rife in philosophy – at least, it's a bit unsettling if you hope to do fundamental work in the subject yourself. Another example would be Nietzsche's writing Zarathustra in the wake of his humiliating falling out with Paul Rée and Lou Salomé.


  1. Replies
    1. Interesting. The notion of 'worlds' you use there forced itself on me too when thinking about this. It seems pretty clearly different from (i) the notion of the world as the totality of everything that exists, or (ii) as the totality of facts, and also different from more artificial notions of 'possible worlds'. As a result, I felt there was something a bit dodgy or less-than-rigorous about using the word in that way. Perhaps interesting work could be done to explore and explicate this special 'world' notion.

  2. The trouble I have with BIVs is exactly "...foul play, planting false memories and moving things around" etc. ISTM they completely dissolve the possibility of principled reasoning.

    A la Matrix, what if you are provided with overwhelming proof that you are a BIV? Do you have hands now?

  3. Overall, I agree. If you are a BIV, then you don't now what kind of hands you have - or perhaps you don't know which sub-category of hands yours belong to. Of much more immediate concern is whether or not you have those hands, (regardless of them being simulated or not).