Putnam Brains in a Vat
Hi everyone,
I am currently working on a project regarding external world skepticism and was just really interested to see if anyone had some interesting thoughts on the topic. I'm particularly focusing on Putnam, Descartes and Moore and their proposed solutions to the dilemma.
However, I am currently struggling to get my head around Putnam's BIV argument in particular. I understand his initial arguments about the necessity of intentionality for representation, however I am struggling to see the connection of this to the culmination of his argument in that it would be self-contradicting for a BIV to declare itself a brain in a vat. Is the point supposed to be that a BIV would not be able to able to explain to a third party what it actually means when it says such a statement given the lack of causal connection between its use of the words brain and vat and its knowledge of the external world objects which these terms represent?
Any help or suggestions would be greatly appreciated! Thanks a million!
I am currently working on a project regarding external world skepticism and was just really interested to see if anyone had some interesting thoughts on the topic. I'm particularly focusing on Putnam, Descartes and Moore and their proposed solutions to the dilemma.
However, I am currently struggling to get my head around Putnam's BIV argument in particular. I understand his initial arguments about the necessity of intentionality for representation, however I am struggling to see the connection of this to the culmination of his argument in that it would be self-contradicting for a BIV to declare itself a brain in a vat. Is the point supposed to be that a BIV would not be able to able to explain to a third party what it actually means when it says such a statement given the lack of causal connection between its use of the words brain and vat and its knowledge of the external world objects which these terms represent?
Any help or suggestions would be greatly appreciated! Thanks a million!
Comments (81)
So it is so alone, that it has no way of knowing it is alone by itself.
It can't have any idea that there is a physical world, therefore it can't have any motivation to communicate with the world.
Therefore his motivation lacking, he has no intention of anything, let alone intention to represent itself.
Furthermore, it may not even have a concept that it, itself is something. Not in a coma, but nevertheless completely devoid of any structural instructions ever, it may not realize its own self.
Long story short: the idea of self-identity is very much contingent upon the views by the self, which views the separation of the self from the outside world generates for the self along with a number of corollaries and considerations. The brain in the vat has no capacity for noticing this separation.
One wonders how Neo in the Matrix could understand what Morpheus was talking about when offered the blue and red pills. And the answer was he could not, he could only be shown. The choice was whether to go down the rabbit hole, or continue living a normal life. It was only after Neo got unplugged that he could understand his situation.
This kind of skeptical scenario is a problem for meaning not being in the head. If the environment provides meaning, but the environment is fake, then one cannot understand the environment being fake. Yet we seem to be able to understand simulation, dream, Matrix and evil demon arguments. So either we can know the environment is not fake, or semantic externalism is false.
Just to be clear: I know that none of us are brains in vats; we are all living in reality.
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.
https://www.scientificamerican.com/article/a-25-year-old-bet-about-consciousness-has-finally-been-settled/
Scientists will keep losing these bets. Eventually, people will abandon the metaphysical assumption that matter exists. Idealism is true. BiV problem solved!
Semantic externalism is a consequence of the causal theory of reference. Words can only refer to things if these things have had some relevant causal affect on the development and use of these words.
If Neo is in the Matrix and there is a tree outside the Matrix then none of Neo's words can refer to this tree. What the word "tree" means and refers to for him isn't what the word "tree" means and refers to for those of us living outside the Matrix.
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.
1. If metaphysical realism is true then we could be brains in a vat
2. If semantic externalism is true then we cannot be brains in a vat
3. Semantic externalism is true
4. Therefore metaphysical realism is false
It isn’t obvious to me that the conclusion is contained in one of the premises.
He starts by defending semantic externalism, then by trying to show that if semantic externalism is true then we cannot be brains in a vat, and so concludes that we are not brains in a vat.
In the earlier argument you gave, I objected to premise 2. I don't consider the argument invalid, but I do consider premise 2 a faulty assumption.
Again, if you lay out the argument, I think we will both have an easier time evaluating Putnam's argument.
Not only that, but the BiV argument removes the entire body, replacing it with "a vat of nutrients which keeps the brain alive" (Putnam, Brains in a Vat). The assumption that the body only keeps the brain alive and does not factor into phenomenal experience is a materialist form of dualism that ought to be dismissed as nonsense.
I am a scientist and I have a human brain in a vat. The brain is conscious, much like me, except its experiences are elicited by a computer directly stimulating the sensory areas of the brain.
None of the words in this brain’s language can refer to the vat because the vat does not stand in the particular causal relationship that is required for it be the referent of a word. Every word in this brain’s language refers only to some feature of its artificial experiences. Even if it has a language that superficially resembles English, what it means by “brain in a vat” isn’t what I mean by “brain in a vat”. What it means by “brain in a vat” is what I mean by “simulated brain in a simulated vat”, and given that it isn’t a simulated brain in a simulated vat, the sentence “I am a brain in a vat” in its language is false.
Agree.
If you prefer, consider instead a body in a vat. It’s the same principle. This person never sees trees, only “hallucinations”, but if the causal theory of reference is true then none of the words in its language can refer to (real) trees.
It’s a real tree given what “real tree” means in my language.
The point still stands that if semantic externalism is true then none of the words in the brain’s language can refer to the vat.
Of course you could just deny semantic externalism, as I do.
I agree with you, but that's different than saying that if semantic externalism is true then we cannot be brains in a vat.
Quoting Michael
Except that the "real tree" might actually be referring to a BiV tree and that's the issue. As you said, if semantic externalism is true, no attempts by us to refer to a "real tree" would be successful if we are in BiV world.
It entails it. No sentence in the brain’s language can refer to the fact that it is a brain in a vat.
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.
Sure. The point is that its experiences are elicited artificially by a computer directly manipulating the sense organs.
It never sees a tree or a brain or a vat and as such no words in its language can refer to these things.
I don't see how it is possible. Much of the sense organs and their sensual periphery point outward, and as such any direct manipulation would require the manipulator to work external to the body, like a sort of VR headset. In that case, he would directly see the headset and would directly refer to that headset, or at least to whatever appears on the screen. I suspect this problem is why Descartes and others need to imagine themselves without bodies in order for their thought experiments to work.
No need for a headset. Just shoot beams of light into the eyes in various shapes and patterns and colours that generate the image of a tree.
I think the point NOS4A2 was making (correct me if I'm missing the mark NOS4A2) is that someone arguing for BiV faces a dilemma. If the person is awake, they are aware that they are BiV. If the person is not awake then they are sleeping or dreaming and are not aware of BiV. In either case, the person is not fooled by BiV.
Not necessarily. You’ve been arguing that we might be brains in a vat despite the fact that we’re not aware that we are.
Even awake, the brain and/or body only experiences what the computer makes it experience. The brain and/or body is cut off from every other kind of external sensory stimulation.
It’s logically possible, and that’s enough for the hypothesis to have philosophical significance.
But wouldn't he be referring directly to the light and the patterns, even if he mistook them for a real tree?
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.
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.
Quoting Michael
Quoting 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?
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 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.
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 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.
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.
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.
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.
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.
Quoting 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.
And what are those reasons?
Quoting NotAristotle
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?
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.”
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.
Quoting 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.
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.
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.
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.
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.
No, because he’s not addressing the argument that we are brains in a vat.
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.
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.
I disagree. When one demonstrates that BIV is physically impossible, scenarios 3 or 4 were never a logical possibility. What was conceptualize from actual functional brains was demonstrated to be false.
Just because one can say or imagine something does not make it possible.
But as a fictitious narrative, one does not need to worry about the support of empirical evidence.
It seems to me that period is gone. Now AI, for example, is focussed on 'What happens next'. And our model of the human is at present just such a creature: body and mind are integrated, and they behave in constant expectation of what happens next.
A brain in a vat seems to me like a ghastly horror movie opinion, thought up by people who think a lot, and live little.
There is a disorder that is called “Thought insertion.” Wikipedia defines it as such, “ Thought insertion is defined by the ICD-10 (International Statistical Classification of Diseases and Related Health Problems) as the delusion that one's thoughts are not one's own, but rather belong to someone else and have been inserted into one's mind. The person experiencing the thought insertion delusion will not necessarily know where the thought is coming from, but makes a distinction between their own thoughts and those inserted into their minds.”
Even more fascinating is the therapy. Again from Wikipedia, “In other words, the patient would speak his thoughts out loud in order to re-give themself the feeling of agency as he could hear himself speaking and then contributing the thought to himself.”
I wonder if such metaphysical reasoning around BIVs could bring on such a disorder as Thought Insertion.
The thing is, if the fact is that you are a brain in a vat, who has been fed all of your perceptions by a mad scientist, then your belief that a brain in a vat is physically impossible is a result of the way your beliefs developed in response to what the mad scientist has been feeding you. So under this scenario you believe what the mad scientist caused you to believe, and so your belief that a BIV is physically impossible doesn't have an informed basis, and would in fact be false.
This is not to say that it is metaphysically possible that you are a BIV , but how could you justify the proposition that it is epistemically impossible?
Yeah, we would experience fabricated evidence that either brains in a vat are possible or aren’t.
The point is that we can’t know whether or not what we see is real or the product of a scientist’s (or evil demon’s) manipulation. So to use what we see as evidence that brains in a vat are impossible is to beg the question and assume that we are not brains in a vat and so can trust what we see.
And that’s precisely why Putnam’s argument is an attempt at refuting metaphysical realism. If metaphysical realism is true then we might be brains in a vat, but we can’t be brains in a vat, and so therefore metaphysical realism is false.
Why did you say we can't be brains in a vat rather than saying that if we were, we could not, even in principle, know that we were?
They might be physically impossible, but if we are brains in a vat then we cannot trust our experience to show us what is physically possible, and so to use what we experience as evidence that brains in a vat are impossible is to beg the question and assume that we are not brains in a vat and so can trust what we experience.
So, we cannot know we are or are not brains in vats, but we can say that it seems way less plausible, and is a conjecture motivated only by it's being a logical possibility, which doesn't mean much. And in any case whether we are real physical beings or brains in vats, since the truth is unknowable, makes no difference to our lives as lived.
Quoting Michael
1. Simply, if the scientist showed that it is physically impossible to have a functional BIV, BIV is not possible. This demonstration might be carried out by use of experiments in which actual brains are studied. These would be the same kind of brains we have studied empirically to understand the role they have biologically in the interaction with the world. This knowledge of the brain is then used by philosophers to construct their thought experiments based on the idea of how brain's function. But if philosophers want to make a claim that the brain placed in an artificial enviorment could function in such a way that would produce simulations, they are obligated to submit themselves to the scientific criticism that comes with the territory.
2. The problem I am seeing here is the philosopher wants to talk about ideas but they also want it to be about the world. So they pull a fast one, they talk about real world objects like brains and vats, accept our empirical understanding of the function of the brain, then use this language to come up with imaginary experiments and suggest all sorts of fanciful outcomes that they claim could really be true.
3. Consider this scenario: An individual claims they have designed a machine that can create energy. When he plugs the machine in he claims that when 100 Joules is inputed to the machine, he will get 200 Joules as output. He claims this is possible based on his design. He plugs it in and the output was 50 Joules. He says to himself, "I guess it was not possible for this machine to create energy." Upon hearing this, a scientist chimes in and says, "this was never possible because it would have violated the law of conservation of energy." Just because you could imagine a design of machine with potential outputs of energy, does not mean it is possible to be realize in the actual world. But some want to insist in saying, "but it is logically possible!" I want to say it is not possible at all but feel free to imagine what you like.
4. I like to say that the idea of BIV is vague at best or nonsense at worst. Basically, what is the scientist suppose to figure out if the idea is too vague and/or nonsense? If you say the scientist is suppose to create a lifetime of a human simulated in the brain, what does that mean? Who are you suppose to talk with to understand this request? If you say the scientist should create an artificial world exactly like our real world, are you comparing an inner world that was pick out by inner ostensive definitions to some external world? But how does this occur? Are we not moving in the territory of what Wittgenstein calls grammatical fictions?
5. Our understanding of the world comes from our use of language in a human community. We have common expressions/reactions to the world. We make similar judgments about objects and events in the world. And language is our vehicle to understand this world. All of this is accomplished through our interactions with other human beings. It is not by observing neuron activity in brains of our fellow human beings. The BIV treats brains like tape recorders, grey matter is the material we record bits of information and play back when we feel like. We don't believe tape recorders, film projectors, computers have rich inner lives, nor should we believe the grey matter in the BIV would also.
You are saying that a BiV brain is different than a real brain, I think. But then tell me this, is BiV perception the same as real perception?
Yeah might as well be flexible and say we can't know what a BIV actually is, but under the scenario what you think of as real perception would necessarily be the same as BIV perception.
What scientist are you referring to? Under this scenario your belief in scientists would be a function of what the mad scientist (god to you) is feeding you in the way of perceptions, so any beliefs about brains that you have would be a function of the virtual reality presented by the mad scientist tending your vat.
The mad scientist might have fed you sensations that resulted in you having a notion of a brain that is utterly unlike what is in the vat. You don't have knowledge of what is in the vat or even the physics of vat world, so you can't have a scientific proof of the impossibility of the thing in the vat in vat world.
That sounds right to my ear wonderer1; BIV perception would have to be the same as real perception, given that BIV perception is the same neuronal activity as real perception.
I will summarize our discussion as it appears to me so far. We both agree, I think, that if it is physically impossible in the real world to put a brain in a vat and simulate reality, then BiV is impossible. But your point of contention is to say that it may be possible to put a brain in a vat and simulate reality in the real world, although a brain in a vat may falsely think that BiV is impossible. In such a case, a BiV brain would have to be constituted differently than a real brain, given that putting a BiV brain in a BiV vat is impossible, although putting a real brain in a real vat is possible.
Now, let us suppose that BiV world has some neuroscientists in it. That seems like a plausible assumption, unless your position is that BiV world cannot contain any neuroscientists. But if that were your position we would have proven that our world is not BiV world. So for now, we may suppose that BiV world contains neuroscientists, and these neuroscientists have a lot of knowledge about brains.
That brings me to the next question I would like to ask you: is BiV brain different than real brain by having more parts or by having fewer parts?
How about this scenario: I can imagine a witch that can cast a spell in which they make some poor soul believe that they are experiencing a world I which they are an autonomous agent thinking for themselves. Is this a logical possiblity? If you say no because it does not fit in with our ideas of causality and scientific world view, this can just be turned around by skeptic where they say "well that's because the witches's spell is making you think that." I would like to say that while this can be imagine it is not possible based on our understanding of causality and scientific world view. For the BIV example, the same goes, if we come to find that the BIV is physical impossible, meaning it can't function like we think, not only is it physical impossible, it would be impossible in general. Basically, experience and testing would show that the idea was ill formed. Whether BIVs, dreams, evil demons, witches, etc., any of these used to demonstrate some radical skeptical position is at its core faulty, useless thinking. This thinking resembles what authors do when they produce fictitious narratives, borrow from their real life experience and make up fantasy tales with no intention of claiming that they are talking about real life events. This type of philosophical thinking is doing the same, but with the delusional attempt in trying to potentially say something of the world we live in.
Wittgenstein's "On Certainty" said it best, "505. It is always by favor of Nature that one knows something."
Perhaps I see more value in considering thought experiments than you do? Einstein's thought experiments played an important role in human understanding of relativity theory. Suppose we consider the merits of thought experiments, as a technology for stimulating human minds to look at things from a different perspective?
Anyway, as far as my best guess regarding the world we live in. I don't see any reason to think that it is physically impossible for a BIV to exist. I don't have any reason for confidence that it will ever be technologically possible for humans to maintain a human BIV capable of philosophical conversations 'in a vat'. Furthermore, if in the future the scientific knowledge and technology necessary to maintain a human brain in a vat is available, I'd expect those with the scientific know how and access to the technology would consider creating a BIV to be a silly (and possibly immoral) thing to do.
If we want to talk in more realistic terms, about what sort of technological minds humans might create, we might look at using a technology like spintronic memristors used to instantiate artificial neural networks.
Quoting Richard B
Well, I'd quibble over whether using the word "favor" is saying it best. I'm inclined to say something more like, "It is always as a consequence of interactions occurring in Nature that one knows something."
The role of imagination in scientific theorizing is not in question. Also, I certainty would not say that philosophy cannot offer insights to a scientist. In nice article by John Norton, "How Hume and Mach Helped Einstein Find Special Relativity", provides a nice summary how these two philosophers, belonging to the empiricist/positivist traditions, influenced Einstein's abandonment of the idea of absolute time and simultaneity. However, even in this article, Einstein echoed what I have been saying. In section 3.1, titled "Concepts Must be Grounded in Experiences", he quotes Einstein, "‘Similarly,’ Einstein continued, ‘with the concept of simultaneity. The concept really exists for the physicist only when in a concrete case there is some possibility of deciding whether the concept is or is not applicable."
wonderer1: I should rather think that a BiV brain cannot be compared to a real brain; they are completely different.
NotAristotle: As you say wonderer1, but then neither you nor I are a brain in a vat. We may be utterly deceived by our senses, but it is not by being a brain in a vat.
wonderer1: But I insist that we are brains in a vat; it must be so.
NotAristotle: Well then when we say brain we must mean something like a real brain.
wonderer1: Very well.
NotAristotle: Let us return then to our original inquiry: you seem to have said that a real brain is different than a BiV brain. But is it different by having more parts or fewer?
wonderer1: Surely it is by having fewer parts NotAristotle.
NotAristotle: Well put wonderer1, for if it had more parts, then it could be placed in a vat, just like a real brain. However, we are saying that it is impossible to place a BiV brain in a BiV vat. And this must be the case on account of a BiV brain having fewer parts than a real brain.
wonderer1: Indubitably.
NotAristotle: And what of our neuroscientists? Will they not be very much surprised to find that parts of our brains are missing?
wonderer1: Perhaps not.
NotAristotle: How do you mean wonderer1?
wonderer1: Perhaps the parts of the brain that are missing are not essential to perception, but are extra parts.
NotAristotle: Ah, I see, so these extra parts are excised, leaving behind the parts that are necessary for BiV perception.
wonderer1: Precisely.
NotAristotle: But if the parts that are necessary for perception are left intact, then once again, it should be possible to place a BiV brain in a BiV vat. But again, we have said this is impossible.
wonderer1: That is so.
NotAristotle: Then the problem arises once again, that our neuroscientists will likely find that parts of the brain are missing that are necessary for perception.
wonderer1: As you say NotAristotle.
NotAristotle: It stands to reason then, that if we are brains in a vat, the evidence will amount to saying that it should be impossible for us to perceive, given that we would be missing parts of the brain that are necessary for perception. In short, if we are brains in a vat, we will be missing parts of our brain, and neuroscientists will be quite perplexed by that.
wonderer1: Surely what you say is true NotAristotle.
NotAristotle: Well then wonderer1 that is good news. For, unless you and I are missing parts of our brains, we are most certainly not brains in a vat.
wonderer1: Good news indeed NotAristotle.