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Are We 'Brains in a Vat?'

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In this famous essay (excerpted below) philosopher Hilary Putnam asks whether we could really be nothing but "brains existing in a vat". I would be curious to hear what others think.

The following excerpt is from Hilary Putnam from Reason, Truth, and History, chapter 1, pp. 1-21

The case of the brains in a vat

Here is a science fiction possibility discussed by philosophers: imagine that a human being (you can imagine this to be yourself) has been subjected to an operation by an evil scientist. The person's brain (your brain) has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. There seem to be people, objects, the sky, etc.; but really, all the person (you) is experiencing is the result of electronic impulses travelling from the computer to the nerve endings. The computer is so clever that if the person tries to raise his hand, the feedback from the computer will cause him to 'see' and 'feel' the hand being raised. Moreover, by varying the program, the evil scientist can cause the victim to 'experience' (or hallucinate) any situation or environment the evil scientist wishes. He can also obliterate the memory of the brain operation, so that the victim will seem to himself to have always been in this environment. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people's brains from their bodies and places them in a vat of nutrients which keep the brains alive. The nerve endings are supposed to be connected to a super-scientific computer which causes the person whose brain it is to have the illusion that...

When this sort of possibility is mentioned in a lecture on the Theory of Knowledge, the purpose, of course, is to raise the classical problem of scepticism with respect to the external world in a modern way. (How do you know you aren't in this predicament?) But this predicament is also a useful device for raising issues about the mind/world relationship.

Instead of having just one brain in a vat, we could imagine that all human beings (perhaps all sentient beings) are brains in a vat (or nervous systems in a vat in case some beings with just a minimal nervous system already count as 'sentient'). Of course, the evil scientist would have to be outside - or would he? Perhaps there is no evil scientist, perhaps (though this is absurd) the universe just happens to consist of automatic machinery tending a vat full of brains and nervous systems.

This time let us suppose that the automatic machinery is programmed to give us all a collective hallucination, rather than a number of separate unrelated hallucinations. Thus, when I seem to myself to be talking to you, you seem to yourself to be hearing my words. Of course, it is not the case that my words actually reach your ears - for you don't have (real) ears, nor do I have a real mouth and tongue. Rather, when I produce my words, what happens is that the efferent impulses travel from my brain to the computer, which both causes me to 'hear' my own voice uttering those words and 'feel' my tongue moving, etc., and causes you to 'hear' my words, 'see' me speaking, etc. In this case, we are, in a sense, actually in communication. I am not mistaken about your real existence (only about the existence of your body and the 'external world', apart from brains). From a certain point of view, it doesn't even matter that 'the whole world' is a collective hallucination; for you do, after all, really hear my words when I speak to you, even if the mechanism isn't what we suppose it to be. (Of course, if we were two lovers making love, rather than just two people carrying on a conversation, then the suggestion that it was just two brains in a vat might be disturbing.)

I want now to ask a question which will seem very silly and obvious (at least to some people, including some very sophisticated philosophers), but which will take us to real philosophical depths rather quickly. Suppose this whole story were actually true. Could we, if we were brains in a vat in this way, say or think that we were?

Well? Could it be true? If you think yes, then maybe you could explain why?
If you think not, then, why not?

Read his full essay here:

@Pythagorean,

Pythagorean wrote:

Well? Could it be true? If you think yes, then maybe you could explain why?
If you think not, then, why not?

Read his full essay here:

If "could it be true?" means only that it is not self-contradictory to suppose it is true, I guess it is not. If it means that there is any real possibility that it is true (it has any plausibility) the answer is obviously, no.

@Pythagorean,

Quote:

If it means that there is any real possibility that it is true (it has any plausibility) the answer is obviously, no.

Why is the answer obviously no? Is there anything about our experiences which give us any reason to think we are not "brains in a vat"?

@Didymos Thomas,

Didymos Thomas wrote:

Why is the answer obviously no? Is there anything about our experiences which give us any reason to think we are not "brains in a vat"?

Suppose the answer to that is, no. Is there anything in our experience to make us think that we are BIV? After all, that is the claim.

Bertrand Russell once hypothesized that the universe was created (along with all of the evidence of the past) five minutes ago. Think that is plausible too?

The fact that something is logically possible is absolutely no reason to think it has any plausibility.

@Pythagorean,

Quote:

Suppose the answer to that is, no. Is there anything in our experience to make us think that we are BIV? After all, that is the claim.

Bertrand Russell once hypothesized that the universe was created (along with all of the evidence of the past) five minutes ago. Think that is plausible too?

The fact that something is logically possible is absolutely no reason to think it has any plausibility.

The BIV possiblity is not merely a matter of being logically possible.

It is logically possible for a cow to jump over the moon; however, we know cows will not jump over the moon because we can empirically establish that such a thing is highly improbable.

In the case of BIV, the situation is logically possible. The question before us is whether or not BIV is empirically probable. Going back to Pythagorean's post, the thought experiment is set up in such a way that the BIV seems as empirically likely as the status quo (that we are not BIV).

The BIV situation is a thought experiment for us to consider so that we can refine our ideas regarding mind and reality. After all, if we cannot know that we are not BIV, that we can know anything about reality is placed in jeopordy.

@Pythagorean,

Quote:

Could We All Be But "Brains in a Vat?"

[/B]

I don't think the statement has any meaning one way or the other, because there is no way that we can verify if we are or are not brains in a vat.

However, we can verify that a cow cannot jump over the moon, thus I do not think that you should handle both statements equally.

(what type of philosopher am I playing?)

--------

It seems like this thought experiment stems from Descartes' mind body dualism. If you accept that it is possible that we are brains in a vat, you have to at the same time accept that it is possible our mind is seperate from our body.

@Pythagorean,

Quote:

I don't think the statement has any meaning one way or the other, because there is no way that we can verify if we are or are not brains in a vat.

Then what can we know if we do not even know if we are and reality is as they appear, or if we are brains in a vat and reality as we know it is illusion?

Quote:

However, we can verify that a cow cannot jump over the moon, thus I do not think that you should handle both statements equally.

A cow can jump over the moon is logically possible, but empirically unlikely (as unlikely as the sun not rising tomorrow). Such an occurence is logically possible; however, our empirical knowledge tells us such an occurence will probably not take place.

That we are brains in a vat is logically possible, and it seems that we are brains in a vat is just as empirically possible as the status quo (that we are not brains in a vat).

Quote:

If you accept that it is possible that we are brains in a vat, you have to at the same time accept that it is possible our mind is seperate from our body.[/quote[

Careful not to confuse the concepts of "mind" and "brain" as they are different even if you think mind is a faculty of the brain.

This thought experiment is similar to Descartes' deceiver - the demon that ensures all of Descartes senses are illusory - because both this TE and Descartes' TE call into question our notions of reality.

@Pythagorean,

Quote:

Then what can we know if we do not even know if we are and reality is as they appear, or if we are brains in a vat and reality as we know it is illusion?

I can empircally validate that I am sitting in front of this computer typing to right now, that I can know. Thus it has factual meaning. (either I actually am, or I am not)

I can not empirically validate that I am not a brain in a vat or that I am a brain in a vat. Thus either of the statements cannot have factual meaning. (either I am or am not is not a question, because I can never even possibly know one way or the other)

Since the statement has no meaning, it has no implications for describing the reality that I experience. It does not matter if I cannot know that I am or am not a brain in a vat, it has no determining factor on my boundries of knowledge. Therefore, I can still have knowledge of many things.

----

It would seem to me that if my brain being in a vat is a possibility, then my knowledge is even more limited than if I know that I am not.

So I will ask your question to you: If it is possible that we are brains in vats, then what can we know?

Quote:

A cow can jump over the moon is logically possible

Can you please provide the logic for me.

Quote:

Careful not to confuse the concepts of "mind" and "brain" as they are different even if you think mind is a faculty of the brain.

If I am a brain in a vat, and my experience of my hand right now is not my hand, but an illusion, then my mind is seperate from my body (the body I am experiencing and have always experienced). Correct?

@Didymos Thomas,

Didymos Thomas wrote:

The BIV possiblity is not merely a matter of being logically possible.

It is logically possible for a cow to jump over the moon; however, we know cows will not jump over the moon because we can empirically establish that such a thing is highly improbable.

In the case of BIV, the situation is logically possible. The question before us is whether or not BIV is empirically probable. Going back to Pythagorean's post, the thought experiment is set up in such a way that the BIV seems as empirically likely as the status quo (that we are not BIV).

The BIV situation is a thought experiment for us to consider so that we can refine our ideas regarding mind and reality. After all, if we cannot know that we are not BIV, that we can know anything about reality is placed in jeopordy.

BIV assumes a certain theory of perception (sometimes called, "direct realism") which is that we never observe objects, but "observe" only our perceptions of objects. Thus, on that view, we are always at inference-length from the world. But, there is really no good reason to think that indirect realism is true, and that we do not simply observe objects. If I observe that I have two hands (or instance) then I could not be a BIV. And I think I have a lot more reason to believe that I can observe my two hands, than I have for believing that I am a BIV.

@Pythagorean,

Quote:

I can empircally validate that I am sitting in front of this computer typing to right now, that I can know. Thus it has factual meaning. (either I actually am, or I am not)

You say that you can empirically validate that you are in front of this computer, but you have not shown how you can do this. The whole purpose of the TE is to determine whether or not we can empirically validate such a claim.

Quote:

So I will ask your question to you: If it is possible that we are brains in vats, then what can we know?

Nothing as far as I can tell.

Quote:

Can you please provide the logic for me.

Nothing about the statement "A cow jumped over the moon" defies the law of noncontradiction.

Quote:

If I am a brain in a vat, and my experience of my hand right now is not my hand, but an illusion, then my mind is seperate from my body (the body I am experiencing and have always experienced). Correct?

Isn' the brain part of the physical body?

Quote:

BIV assumes a certain theory of perception (sometimes called, "direct realism") which is that we never observe objects, but "observe" only our perceptions of objects.

BIV assumes nothing - BIV is a thought expiriment, a TE that asks the question 'How do we know, can we know, that we are not BIV?'

Quote:

If I observe that I have two hands (or instance) then I could not be a BIV.

Why does the apparent observation of having two hands establish that the observation of those two hands is not an illusion per the TE?

Quote:

And I think I have a lot more reason to believe that I can observe my two hands, than I have for believing that I am a BIV.

Perhaps, but I would be interested in hearing these reasons. How do you know that what you observe is not illusory?

@Didymos Thomas,

Didymos Thomas wrote:

Perhaps, but I would be interested in hearing these reasons. How do you know that what you observe is not illusory?

I have no reason to think that it is illusory. Have you any reason to think that it is, besides the speculation that I am a BIV, which is, after all, what is at issue.

As I pointed out, the BIV speculation supposes a theory of perception which tells us that we perceive only our own perceptions (whatever that means) and never perceive objects. So that we are always "locked" into our own perceptions. But I don't think that is true (and neither do you).

@kennethamy,

kennethamy wrote:

...the BIV speculation supposes a theory of perception which tells us that we perceive only our own perceptions (whatever that means) and never perceive objects. So that we are always "locked" into our own perceptions. But I don't think that is true (and neither do you).

Which means that we may be BIVs but unless we have clear and rational proof of the opposite, then we have reasonable doubt to believe that we are anything but BIVs.

@Aristoddler,

Aristoddler wrote:

Which means that we may be BIVs but unless we have clear and rational proof of the opposite, then we have reasonable doubt to believe that we are anything but BIVs.

It means only that it is not logically impossible that we are BIV, which is to say, it is not self-contradictory to suppose that we are BIV. But how does that mean that it is reasonable to doubt that we are not BIV?

It is not logically impossible that there is a Flying Spaghetti Monster, which is to say that it is not self-contradictory to suppose that there is a Flying Spaghetti Monster. But how does that mean it is reasonable to doubt that there is no Flying Spaghetti Monster?

That the supposition of the existence of something is not self-contradictory, in no way shows that it is not reasonable to doubt that there is is such a thing.

To prove something beyond all doubt is one thing; to prove something beyond all reasonable doubt is a different thing.

It is not true that we may be BIVs. For, it does not follow from its being logically possible that we are BIVs, that we may (that it is reasonable to believe) that we are BIV's. Something can be not self-contradictory, and it not be reasonable to suppose that it is true. E.G. The Flying Spaghetti Monster.

@Pythagorean,

Sure I could be a brain in a vat. If I am then my jailer is pretty impressive. I'd like to meet the designer of my delusions someday and congratulate it on it's ingenuity. Smile

@Quatl,

Quatl wrote:

Sure I could be a brain in a vat. If I am then my jailer is pretty impressive. I'd like to meet the designer of my delusions someday and congratulate it on it's ingenuity.

The question is, in what sense of "could" could you be a BIV. In, I suppose, the sense in which you could be the Flying Spaghetti Monster. In no way is that the customary sense in which we think that something could be true. And, I suppose, that is just what anyone who says that we could be BIV counts on.

@kennethamy,

kennethamy wrote:

The question is, in what sense of "could" could you be a BIV. In, I suppose, the sense in which you could be the Flying Spaghetti Monster. In no way is that the customary sense in which we think that something could be true. And, I suppose, that is just what anyone who says that we could be BIV counts on.

But I don't feel like a flying spaghetti monster! I do feel exactly like a brain in a vat being fed sensations via the torn stumps of my peripheral nervous system.

The sense in which I mean "could" is that the results of the scenario fit my phenomenological experience. There are many other scenarios which share this quality, among those possibilities is the one where I am a human on earth going about my business.

I choose to believe this later one, in case you are fearing for my sanity... then again If we are vat brains, my favoring this version of things would mean that I'm insane by definition.

My reasons for favoring the later option are in fact irrational, for the only reason I have to base such a judgment is derived from the very experience that the scenario brings into question. Which is of course the history of my own life and what I've witnessed.

@Quatl,

Quatl wrote:

But I don't feel like a flying spaghetti monster! I do feel exactly like a brain in a vat being fed sensations via the torn stumps of my peripheral nervous system.

The sense in which I mean "could" is that the results of the scenario fit my phenomenological experience. There are many other scenarios which share this quality, among those possibilities is the one where I am a human on earth going about my business.

I choose to believe this later one, in case you are fearing for my sanity... then again If we are vat brains, my favoring this version of things would mean that I'm insane by definition.

My reasons for favoring the later option are in fact irrational, for the only reason I have to base such a judgment is derived from the very experience that the scenario brings into question. Which is of course the history of my own life and what I've witnessed.

Just what has feeling to do with it? The point is that even if it is true (and I am not so sure of it) that there is no contradiction in my being a BIV, nor any contradiction between my evidence that I am not a BIV, and being a BIV, that is still no reason to think it is even plausible that I am a BIV. The sheer possibility that I am one is not reason at all to think I am one. That is one thing. But another, and different thing is a certain assumption about how we know about the world. An assumption without which the BIV scenario cannot even get off the ground. The assumption is that all our beliefs about the world are inferences from what we directly know, what is sometimes called "the given" which consists of perceptions or sensations. I reject that picture of how we know about the world, since I think it obvious that we directly perceive objects in the world, and that our knowledge of the world is solely inferential. In fact, there is good reason to believe that rather than our knowledge of objects being inferences from our private sensations, it is rather that our belief that we have private sensations is an inference from our (direct) knowledge of objects.

@kennethamy,

kennethamy wrote:

I reject that picture of how we know about the world, since I think it obvious that we directly perceive objects in the world, and that our knowledge of the world is solely inferential. In fact, there is good reason to believe that rather than our knowledge of objects being inferences from our private sensations, it is rather that our belief that we have private sensations is an inference from our (direct) knowledge of objects.

I'd be interested in elaboration on this. What exactly do you mean? I think we may disagree fundamentally but I'm not sure what you're saying and I don't want to be unfair.

@Quatl,

Quatl wrote:

I'd be interested in elaboration on this. What exactly do you mean? I think we may disagree fundamentally but I'm not sure what you're saying and I don't want to be unfair.

Just that the notion that we have private sensations is a theory. We do not observe what some call our sensations of red.
And, even if we do have these private sensations, they are how we see objects. It is the objects (tables and chairs) we see. The sensations are not "premises" from which we infer objects. There is no good argument (that I can tell) that we do not observe tables and chairs.

The very notion of the BIV is based on the notion that we never see tables and chairs, so that we might have the sensations (which we do observe) without the tables and chairs. There is no reason to think that the world might be one big hallucination.

@kennethamy,

kennethamy wrote:

Just that the notion that we have private sensations is a theory. We do not observe what some call our sensations of red.
And, even if we do have these private sensations, they are how we see objects. It is the objects (tables and chairs) we see. The sensations are not "premises" from which we infer objects. There is no good argument (that I can tell) that we do not observe tables and chairs.

The very notion of the BIV is based on the notion that we never see tables and chairs, so that we might have the sensations (which we do observe) without the tables and chairs. There is no reason to think that the world might be one big hallucination.

Our sensory apparatus (most of which is in the brain not in the nose or eye) does appear to have a large amount of "knowledge" about the world, however not in the sense of "chair" but rather information about how light reflects from various surfaces, and such.

Qualities of "Chariness" do not appear in the sensory information at all but are "judgmental" aspects of mind function that has nothing to do with the external world at all.

This is why it is possible for us to imagine, and dream of chairs that we have never beheld. Indeed this is necessary for us to be able to talk of chairs in a general way at all.

As I mentioned above, our vision process draws from a remarkably detailed model of "how the world works" in regard to the behavior of light. The particular visual illusions that we are subject to illustrate the contents of this body of knowledge.

The reason we are prone to optical illusions is because the problem of visual perception is intractable at best (some mathematicians go as far as impossible) if the information is the projection of light on the retina. The particularities of the illusions we can experience are a necessary by product of the specific process through which we resolve information about light behavior in circumstances that are typical in the world.

If we were directly perceiving objects as you say, there would be no reason for the existence of optical illusions.

Not related to justifying the silliness of this thread, you may find it interesting to study the biology of the visual perception process.

So it is on biological grounds that I disagree with your proposition that we in any sense "directly perceive" objects. I think the biology of our senses makes a pretty clear argument that we do not "receive" chairs through our eyes in any meaningful sense.

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