Sure, in that case he can refer to light and shapes and colours just as we can. But he can’t refer to trees and brains or truthfully claim that the things he sees are fabrications.

He could truthfully claim the things he sees are fabrications if he reaches out for the tree and discovers that there is no tree there, that it is some sort of light.

I was being overly simplistic. It’s not just vision that’s being fabricated but all the senses. You don’t really seem to be addressing the actual hypothesis.

There’s just no prima facie reason to suggest that experiences like ours cannot be elicited artificially. There’s nothing magic about the workings of the brain or the body as you seem to agree.

That’s fair. I’m mostly addressing the hypothesis that one can somehow wire up a human being and go around the senses themselves and illicit a similar experience. I think the fact that both Putnam and Descartes remove the senses and the rest of the body from their thought experiment is telling, as if experience could occur without blood and bones and lungs.

Other more fundamental perceptual and sensual cues would be absent, for instance the perception of up and down, the effects of gravity, wether one is standing or sitting, or the fact that he forever has to see his own nose in his periphery, not to mention that such a being could never be alive in the first place.

So in my mind there are plenty of reasons why “experiences” cannot be illicit artificially, and that’s because the body cannot be replaced by a machine and still be considered alive, let alone experience anything.

If BiV is phenomenally the same as not-BiV, then I don't see how semantic externalism can do any work. Even someone who is not-BiV would not know what they meant by real and not real. — NotAristotle

Given that if metaphysical realism is true then something like us living in the Matrix is possible, Putnam's argument is that metaphysical realism and semantic externalism are incompatible, and because he believes that semantic externalism is true he concludes that metaphysical realism is false. — Michael

To be the same principle the body would in some way need to be silenced, or asleep, or unconscious, as in the movie Matrix. Of course, in these states he wouldn't be seeing or hallucinating anything, but dreaming. If the rest of the body is included, awake, and in full working order it would notice that it is in a vat, that it cannot move, is suspended in some sort of liquid, and so on, and his words could directly refer to the environment. — NOS4A2

I am curious, do you all believe that a "BiV" is possible? If so, why do you believe it is possible? Just because you can imagine it?

2. If semantic externalism is true then we cannot be brains in a vat — Michael

Should this be, "If semantic externalism is true then we cannot claim to be brains in a vat"?

But even that doesn't seem right. A BiV can experience an in-world simulation. Suppose a BiV denizen plays SimTree on their (simulated) computer. It may then wonder, "suppose there is a tree that stands in relation to the tree outside my window, in the same way the tree outside my window stands to SimTree"?

After all we do this same sort of thing, hypothesize the existence of things that we have no direct experience of. We can happily use language to refer to these theoretical entities. If a theory eliminates a real feature of real language, chuck it.

I do not believe BiV is possible. I believe semantic externalism doesn't prove that BiV is impossible; I think BiV is impossible for other reasons.

I am curious, do you all believe that a "BiV" is possible? If so, why do you believe it is possible? Just because you can imagine it? — Richard B

I certainly think it’s logically possible, and so if semantic externalism entails that it isn’t logically possible then semantic externalism is false.

I think it may even be physically possible. It is in principle much like a Boltzmann brain, and physicists seem to accept that they are physically possible.

But of course if we are brains in a vat then it may be that “real” physics isn’t exactly like the fabricated physics that we are being programmed to experience, and so one cannot really use physics to disprove the physical possibility of brains in a vat without begging the question.

Should this be, "If semantic externalism is true then we cannot claim to be brains in a vat"? — hypericin

Much like with Tarski's theory of truth, to make sense of this we need a meta language and an object language.

The meta language is the language of the scientist and the object language is the language of the brain. In the meta language the sentence "this is a brain in a vat" is true and in the object language the sentence "I am a brain in a vat" is false because the words "brain" and "vat" in the object language do not refer to what the words "brain" and "vat" refer to in the meta language.

No words in the object language can refer to what the words "brain" and "vat" refer to in the meta language (if semantic externalism is true).

Given this, it must be that the sentence "I am a brain in a vat" in my language is false, and so I am not a brain in a vat (this is simply Tarski's T-schema).

I suppose a simple modus tollens would be:

1. If it is possible that we are brains in a vat then a brain's language can refer to objects outside its simulation
2. A brain's language cannot refer to objects outside its simulation (as per semantic externalism)
3 .Therefore, it is not possible that we are brains in a vat

Personally, I reject 2.

I think the fact that both Putnam and Descartes remove the senses and the rest of the body from their thought experiment is telling, as if experience could occur without blood and bones and lungs.

Other more fundamental perceptual and sensual cues would be absent, for instance the perception of up and down, the effects of gravity, wether one is standing or sitting, or the fact that he forever has to see his own nose in his periphery, not to mention that such a being could never be alive in the first place. — NOS4A2

I don't see a problem with it. I think experience happens in the brain, albeit usually as a response from stimulation by signals sent from the rest of the body. I think it's plausible that we can bypass our sense organs and artificially stimulate the appropriate areas of the brain to elicit the relevant experiences.

For example, see Dynamic Stimulation of Visual Cortex Produces Form Vision in Sighted and Blind Humans.

Or in the more complex case consider Boltzmann brains, which physicists seem to accept as physically possible.

Given this, it must be that the sentence "I am a brain in a vat" in my language is false, and so I am not a brain in a vat (this is simply Tarski's T-schema). — Michael

I'm not following this. If you accept semantic externalism, the object language "I am a brain in a vat" does not and cannot speak to the meta language assertion that the speaker is a brain in a vat. If the "two languages" are split apart, then the falsity of a claim in the one can't imply the falsity of the other.

I'm not following this. If you accept semantic externalism, the object language "I am a brain in a vat" does not and cannot speak to the meta language assertion that the speaker is a brain in a vat. — hypericin

Exactly.

I am a brain in a vat iff “I am a brain in a vat” is true (Tarski’s T-schema).

“I am a brain in a vat” is only true if such a sentence refers to a state of affairs that is “outside” the world I experience.

“I am a brain in a vat” doesn’t refer to a state of affairs that is “outside” the world I experience (semantic externalism).

Therefore “I am a brain in a vat” is false.

Therefore I am not a brain in a vat.

I am a brain in a vat iff “I am a brain in a vat” is true — Michael

But the first part is (presumably) not expressing what the second part is, as they are (presumably) different languages. So Tarski doesn't apply.

I don’t believe experience happens in the brain. When I shake someone’s hand I believe I experience the situation with my entire body, since the entire thing is being used to perform the act. My trouble is with the biology of it. My question is: How can one take every experience of a handshake, from standing to grasping someone’s hand to leaning forward etc, and put all that as an experience in the brain?

Stimulating the visual cortex with electrodes in the blind is a far cry from mimicking reality. I’m not sure how the one can make possible the other.

I think it is fair to say that human beings are more than brains, and that any brain is so interconnected to the rest of the body that to separate one from the other is to end the human being.

When I shake someone’s hand I believe I experience the situation with my entire body, since the entire thing is being used to perform the act. My trouble is with the biology of it. My question is: How can one take every experience of a handshake, from standing to grasping someone’s hand to leaning forward etc, and put all that as an experience in the brain? — NOS4A2

That seems to be what our study of human biology shows. Much like with the case of phantom limb syndrome, the human brain is able to make it seem as if the experience extends beyond its actual location.

The nerves in my fingers might send signals to the brain, but it is brain activity that produces the actual tactile percept. That same tactile percept can be produced artificially by direct stimulation of the somatosensory cortex without the need to stimulate touch receptors in the skin.

Stimulating the visual cortex with electrodes in the blind is a far cry from mimicking reality. — NOS4A2

Maybe it doesn't. Perhaps we are brains in a vat and actual reality is nothing like the world we experience. That's really the entire skeptical hypothesis.

I do not believe BiV is possible. I believe semantic externalism doesn't prove that BiV is impossible; I think BiV is impossible for other reasons. — NotAristotle

And what are those reasons?

It seems to me that having an experience of eating pizza cannot be simulated. That is because my experience of reality requires more than BiV, it requires sensory organs that can experience the reality. The proof is in the pudding, or in this case, the pizza. I think that if you remove the sensory abilities of the organism, you remove phenomenal consciousness too, or at least you remove the phenomenal consciousness of what is sensed. Experience is a more integrated process than just brain processing, in my opinion. — NotAristotle

Let's suppose I am a brain in a vat, but I have fully functioning eyes. In front of me is a green screen. Still, a scientist stimulates my occipital lobe to see green. What do I see? The real green or the simulated green?

I think it is fair to say that human beings are more than brains, and that any brain is so interconnected to the rest of the body that to separate one from the other is to end the human being. — NOS4A2

Sure.

However. people who think seriously about the subject recognize that different parts of the human body do different things. What the brain does seems to be of particular interest. Do you disagree?

think it may even be physically possible. It is in principle much like a Boltzmann brain, and physicists seem to accept that they are physically possible.

But of course if we are brains in a vat then it may be that “real” physics isn’t exactly like the fabricated physics that we are being programmed to experience, and so one cannot really use physics to disprove the physical possibility of brains in a vat without begging the question. — Michael

I will not address the Boltzmann brain (as there is another thread for that) but go with the current scientific theory that human brains are a product of millions of years of evolution. What if scientists biologically demonstrate that the BIV cannot function like a brain with a human body (the brain just degrades when artificially stimulated). However, as you put it, this does not refute the possibility that this experience of “scientists demonstrating the BIV cannot function” was not fabricated in some BIV. But why should we say logical possibility trumps physical impossibility? Ours ideas are derived from our experiences of physical brains. The manifestation of a functional brain is a human being who articulates what is possible and impossible against a background of an external world. How should we think of an idea that says, “it was fabricated in a BIV to think it was fabricated in a BIV.”? This idea has all the qualities of a fiction, not either true/false or possible/impossible. This is where this type of metaphysical reasoning fails, it starts out trying to say something about the world in which we live in, but quickly degrades into phantasm where it logically excluded any verification, falsification, confirmation gathered by our experiences.

I am reminded of a quote from David Hume from Dialogues Concerning Natural Religion; where he thoroughly criticizes the metaphysical design argument for the existence of God, “A total suspense of judgment is here our only reasonable resource.”

However, as you put it, this does not refute the possibility that this experience of “scientists demonstrating the BIV cannot function” was not fabricated in some BIV. But why should we say logical possibility trumps physical impossibility? — Richard B

If we are brains in a vat then us being a brain in a vat isn't a physical impossibility, even if our fabricated world suggests otherwise.

To use the world we experience as empirical evidence that brains in a vat are physically impossible is to beg the question and assume that we are not brains in a vat.

This is where this type of metaphysical reasoning fails, it starts out trying to say something about the world in which we live in, but quickly degrades into phantasm where it logically excluded any verification, falsification, confirmation gathered by our experiences. — Richard B

At least according to metaphysical realists, something can be true even if it can neither be verified nor falsified. This is central to Putnam's argument. Metaphysical realism entails global skepticism ("we could be brains in a vat"), and so if he can prove that we cannot be brains in a vat then he can disprove metaphysical realism.

Sure.

However. people who think seriously about the subject recognize that different parts of the human body do different things. What the brain does seems to be of particular interest. Do you disagree?

Obviously it is of more interest than the foot, and people spend a great deal on it, but should that be the case? I’m not so sure. For instance, the question of where the brain ends and the rest of the body begins is in my mind insoluble. The carotid arteries, the spine, the endocrine system—all are intimately connected, and are therefor one thing. Removing the rest of the body from a theory of mind is a huge but fairly common mistake.

Obviously it is of more interest than the foot, and people spend a great deal on it, but should that be the case? I’m not so sure. For instance, the question of where the brain ends and the rest of the body begins is in my mind insoluble. The carotid arteries, the spine, the endocrine system—all are intimately connected, and are therefor one thing. Removing the rest of the body from a theory of mind is a huge but fairly common mistake. — NOS4A2

The topic is a thought experiment that doesn't need to be nomologically viable to stimulate epistemological consideration of it.

Choosing to consider a brain in a vat as compared to a human body in a vat seems to be an attempt to simplify things to a sort of minimum system for epistemic relevevance, and you seem intent on missing the point.

It’s more of an attempt to say the vat represents the body, shedding what is necessarily a fundamental factor of mind and self in favor of an untenable view of mind and self as brains. The thought experiment is evidence of a brain/body dualism not that much different than mind/body dualism. Premising epistemological considerations on the absurd is little more than navel gazing, in my opinion.

To use the world we experience as empirical evidence that brains in a vat are physically impossible is to beg the question and assume that we are not brains in a vat. — Michael

Nicely put, but I would have to disagree here. If a physicist says it is physically impossible for something to travel faster than the speed of light, are they begging the question? In this scenario, the scientist is not assuming we are not brains in a vat, they would be empirically demonstrating that the idea of a brain in a vat cannot function the way a brain in human does with its natural environment.

It is the philosopher bringing in its own metaphysical baggage that gets them all tied up in a knot. The scientist is trying say something of this world, the philosopher is pretending to, but in the end they are just creating fairy tales.

But of course if we are brains in a vat then it may be that “real” physics isn’t exactly like the fabricated physics that we are being programmed to experience, and so one cannot really use physics to disprove the physical possibility of brains in a vat without begging the question. — Michael

Is the unseen scientist fabricating you to think that this is plausible, or the unseen scientist fabricating me to say it is not plausible to fabricating these thoughts? But this sounds strange, are you saying that we are not free agents making rational arguments for or against this idea of the BIV? Sounds like we are mere tape recorders for some unseen entity. This entity can fabricate physics and fabricate logic, I guess what follows would be that it would difficult to have a conversation with such an entity. Damn, never mind, that was fabricated too.

If a physicist says it is physically impossible for something to travel faster than the speed of light, are they begging the question? — Richard B

No, because he’s not addressing the argument that we are brains in a vat.

If a neuroscientist gave you evidence that a brain could not be stimulated in such a way so as to produce simulated percepts, would you be convinced that the brain in a vat hypothesis is impossible?

If a neuroscientist gave you evidence that a brain could not be stimulated in such a way so as to produce simulated percepts, would you be convinced that the brain in a vat hypothesis is impossible? — NotAristotle

Many are willing to accept the scientific evidence of what the brain does to kick start the thought experiment that we could be BIVs. But as soon as you discuss the possibility of introducing scientific evidence to show that a BIV is not possible, it suddenly is “begging the question”, or that evidence was somehow fabricated in the scientist’s mind.

Exactly. That's what I am thinking too -- if the empirical evidence that establishes BiV is accepted, then why is any other empirical evidence ignored?

These are the logically possible scenarios:

1. We are not brains in a vat and the evidence suggests that brains in a vat are physically possible

2. We are not brains in a vat and the evidence suggests that brains in a vat are physically impossible

3. We are brains in a vat and the evidence suggests that brains in a vat are physically possible

4. We are brains in a vat and the evidence suggests that brains in a vat are physically impossible

If the evidence suggests that brains in a vat are physically possible then we are in either 1 or 3.

If the evidence suggests that brains in a vat are physically impossible then we are in either 2 or 4.

We can’t have empirical evidence that rules out 4.