If you are a brain in a vat, there are possible experiences that could inform you of that, e.g. if the people running the vat want you to know it.

So being a brain in a vat is in principle discernible from being a real normal person, so they are not in fact identical.

That out of the way, consider the fact that life as a brain in a vat is indiscernible from life as an actual human being. If so, it follows, from 2. identity of indiscernibles, that life as a brain in a vat is identical to life as an actual human being in the sense that they're the exact same thing. — TheMadFool

Unless you describe life as an actual human being as being a brain in the vat, then the two are not the same thing. We generally describe life as an actual human being as something other than being a brain in a vat, so we do not have this problem. It's only a problem if you think that life as a human being is nothing other than being a brain in a vat.

If you are a brain in a vat, there are possible experiences that could inform you of that, e.g. if the people running the vat want you to know it.

So being a brain in a vat is in principle discernible from being a real normal person, so they are not in fact identical. — Pfhorrest

Firstly, this world and this life we're living are such that we can't discern whether we're actual human beings or brains in vats. Call the experience of this world X.

A you correctly pointed out, to know whether we're brains in vats (or actual human beings) we need information.

There are two things to consider:

1. The gateway for information necessary to know we're brains in vats is our senses

2. Our senses are totally unreliable (can be manipulated) to discern our true status. After all isn't this precisely why we're unable to distinguish whether we're brains in vats or actual human beings?

Ergo, we can never know, for sure, that we're actually brains in vats.

I'm curoious though. What would the information that could help us know we're brains in vats look like?

Unless you describe life as an actual human being as being a brain in the vat, then the two are not the same thing. We generally describe life as an actual human being as something other than being a brain in a vat, so we do not have this problem. It's only a problem if you think that life as a human being is nothing other than being a brain in a vat. — Metaphysician Undercover

Can you tell the difference between being a brain in a vat and an actual human being from our vantage point?

Firstly, this world and this life we're living are such that we can't discern whether we're actual human beings or brains in vats. Call the experience of this world X. — TheMadFool

The fact that you or I, both of us, or a whole bunch of people, cannot discern one thing from another thing, does not necessitate the conclusion that the two are indiscernible. Being indiscernible, which means that it is impossible to discern, is not relative to the human capacity for discerning.

What would the information that could help us know we're brains in vats look like? — TheMadFool

A figure could appear out of thin air and tell you so, and demonstrate anything else you might want to see as evidence... like say, a feed from outside the vat, showing your brain being prodded or whatever, and the corresponding changes in your perception of reality.

But more generally speaking, if there is any way for the world outside the vat to influence our perceptions in the vat, we have some way of getting information from outside the vat. And if the things we do in the vat have any influence on the world outside the vat, then we can do something in here to provoke responses out there that then have some effect on us in here.

The exact nature of what those interactions across the vat boundaries look like depends on how exact the vat is set up, which is one of the things we would want to figured out by trying to provoke reactions out there. If so far nothing we do in here provokes any reactions out there that have observable consequences in here, then so far as we can tell we are not brains in vats. But if we are brains in vats, then in principle some things we do in here will have some consequences out there, some of which in turn will have some consequences in here, though which we could eventually tell.

The fact that you or I, both of us, or a whole bunch of people, cannot discern one thing from another thing, does not necessitate the conclusion that the two are indiscernible. — Metaphysician Undercover

That's a contradiction. I think you need to give another look at the issue.

The exact nature of what those interactions across the vat boundaries look like depends on how exact the vat is set up, which is one of the things we would want to figured out by trying to provoke reactions out there. — Pfhorrest

That is known - we're a brain in a vat

What's crucial is that we can't rely on our senses. So, no amount of information through them will ever be sufficient to let us know anything about our status as brains in vats or actual human beings.

What's crucial is that we can't rely on our senses. — TheMadFool

That’s begging the question.

The brain in a vat scenario tries to establish THAT we can’t rely on our senses. My rebuttal to it proceeds from the assumption that we can.

That’s begging the question.

The brain in a vat scenario tries to establish THAT we can’t rely on our senses. My rebuttal to it proceeds from the assumption that we can. — Pfhorrest

:chin: The brain in a vat thought experiment is to show that reality could be a simulation based on the fact that our senses are unreliable. I think you've got it backwards.

That's a contradiction. I think you need to give another look at the issue. — TheMadFool

Huh? The fact that I cannot discern the difference between two things, does not necessitate the conclusion that the difference is indiscernible.

Do you recognize the difference between "I cannot do X", and "X cannot be done"?

:chin: The brain in a vat thought experiment is to show that reality could be a simulation based on the fact that our senses are unreliable. I think you've got it backwards. — TheMadFool

Pretty sure you’ve got it backwards here. It’s an update on the Evil Demon: both are trying to show that the senses are unreliable because they could be being fed false input, in a magical illusion or virtual reality.

I’m saying that we could in principle discern that we were being deceiving, eventually. These far-fetched scenarios just make that much harder.

Pretty sure you’ve got it backwards here. It’s an update on the Evil Demon: both are trying to show that the senses are unreliable because they could be being fed false input, in a magical illusion or virtual reality.

I’m saying that we could in principle discern that we were being deceiving, eventually. These far-fetched scenarios just make that much harder. — Pfhorrest

You're mistaken. Read the links. Descartes conclusion isn't that our senses are fallible but that reality could be an illusion (from senses beimg fallible) To show our senses are fallible we'd have to use hallucinations or the like as evidence.

Huh? The fact that I cannot discern the difference between two things, does not necessitate the conclusion that the difference is indiscernible.

Do you recognize the difference between "I cannot do X", and "X cannot be done"? — Metaphysician Undercover

As I mentioned earlier, all information flows into our brains/minds through our senses. Our senses being fallible, it's impossible to know whether what we see as discernible differences are actually differences. Presumably all beings are functionally similar to us.We cannot discern X implies that X cannot be done.

You're mistaken. Read the links. Descartes conclusion isn't that our senses are fallible but that reality could be an illusion (from senses beimg fallible) To show our senses are fallible we'd have to use hallucinations or the like as evidence. — TheMadFool

I have, and also, I've studied this professionally for years, including a term entirely about Descartes.

Descartes is trying to show that we can doubt the things our senses show us, and thus that what we think we know about reality might not be so. To show this he gives a lot of examples and hypotheticals about the senses being deceived, including ultimately the Evil Genius scenario in which all of the senses have always been fed entirely false information. The Brain in a Vat is an updated version of that same latter scenario. Its thesis is that we can't trust what our senses tell us about reality, because someone could be feeding our senses completely false information all the time.

I'm saying, translated back to the Evil Genius version of it for clarity here: maybe we can't directly tell anything about the external world, if there is one, but we can tell something about the Evil Genius himself, based on how he reacts (in the form of the false experiences he sends us) to things we do; and if there is a world that Evil Genius is in, like if he is actually a scientist experimenting on our brain in his vat, we can in principle tell something about it through his reactions to it. Or more generally, on how that external world affects our brains, even being in the vat as they are, especially in response to things we do, even being brains in vats as we are. Because if there is absolutely no communication between our brains and the world outside the vat, no signals at all being sent between them, then we are completely causally isolated from each other, and in effect are not in the same universe at all. If we are not thus isolated -- like, if people in the outside world could poke our brains with sticks, or shoot them with lasers, or see them because light can bounce back and forth -- then there is some channel of communication between the brain and the world outside the vat, that in principle can somehow be exploited to tell information about that world. The vat just makes it a lot harder than it otherwise would be if we had normal eyes etc.

But hey, we can now watch objects that emit and reflect no light at all (black holes) that are hidden forever beyond a veil of primordial glow from the big bang (the CMB), so far away from us that we will never be able to send a signal back to them, thanks to gravitational wave detectors. And there are tricks to get information off of computers in sealed rooms that aren't connected to any network, or to use software to induce physical failures in hardware at the quantum level and so enable software exploits to break hardware security. If there is any possibility of interaction between two systems, somehow it is possible to send and receive information between them.

Ok. Good to know you've invested time on the topic. All the more reason for me to seek your views on the matter. :smile:

Firstly, we can't deny the fact that it's impossible (for us, according to you) to tell whether we're brains in vats or actual human beings. This is because there's what I call the middle man, our sensory apparatus that can be manipulated, perhaps by electrically stimulating it, to give us experiences of things without the things actually existing - basically, what we think is reality could be simply a simulation. If so, we being brains in vats enters into the realm of possibility.

Given this, we must realize that anything that has been touched by the middle man is unreliable. The problem, as I see it, is that there's no way of getting rid of the middle man - there's no way for us to directly sense beyond what the middle man let's us sense.

Analogous to a person locked up in a room with the only access to the world outside being a single monitor on a desk, we're utterly helpless. Being so, no amount of information, since it has to pass through the (corrupt) middle man will ever be sufficient for us to infer the true status of our existence as brains in vats or not.

One thing I want to run by you for your inspection is this: is it plausible to say that, if and when the experimenters provide us, brains in vats, information that'll let us know that we are brains in vats, this could be an actual human being suffering from hallucinations?

We cannot discern X implies that X cannot be done. — TheMadFool

This is incorrect, because a being with superior capacities might be able to do X. One cannot conclude from one's own inability to do something, that it is impossible to do that something. "You can't do it" represents your relation with the object. "I can't do it" represents my relation with the object. "We can't do it" represents our relation with the object. "It can't be done" represents the object in an absolute way, in relation to everything else.

$\forall x \forall y: \forall P ( P(x) \leftrightarrow P(y)) \rightarrow x=y$ isn't
$\forall x \forall y: \forall P (K(P(x)) \leftrightarrow K(P(y))) \rightarrow x=y$ where $K$ is the knowledge operator.

There is a property P that readily distinguishes vat-world and not-vat-world, namely whether that entity is part of a simulation of a brain in the vat or not. The ability to know whether something is or is not a simulation is different from whether that something is a simulation. If you want to feed that kind of claim into the identity of indiscernibles, you'd need to establish:

$\forall P \forall x \forall y (K(P(x)) \leftrightarrow K(P(y))) \leftrightarrow (P(x) \leftrightarrow P(y))$

which has $K(P(x)) \leftrightarrow P(x)$ as a consequence - and you end up with both infallibilism and that all truths are known, both theorems of that assumption. Not a good situation.

This is incorrect, because a being with superior capacities might be able to do X. One cannot conclude from one's own inability to do something, that it is impossible to do that something. "You can't do it" represents your relation with the object. "I can't do it" represents my relation with the object. "We can't do it" represents our relation with the object. "It can't be done" represents the object in an absolute way, in relation to everything else. — Metaphysician Undercover

Yes, I get what you mean - "a being with superior capacities" could discern what to us, all of us, is indiscernible.

Firstly, what would the structure of such a being look like? If it's structure resembles ours, specifically if it too depends on some sensory apparatus to interact with what it thinks is reality, then it's back to square one - it can't draw any definitive conclusions from what its sensory apparatus feeds it. Basically, it can't discern its own status as an independent, external observer privy to information we're not.

Secondly, for the above reason it must be that if we can't discern then it can't be discerned, assuming what was said in the previous paragraph.

Firstly, what would the structure of such a being look like? — TheMadFool

This is not relevant. Leibniz does not qualify "indiscernible" with "to us", or with reference to any other type of being with specific capacities for discerning. So we must acknowledge that "indiscernible" was being used without any such qualification, and therefore interpret it in an absolute sense, as it was used.

This is not relevant. Leibniz does not qualify "indiscernible" with "to us", or with reference to any other type of being with specific capacities for discerning. So we must acknowledge that "indiscernible" was being used without any such qualification, and therefore interpret it in an absolute sense, as it was used. — Metaphysician Undercover

Not relevant :chin: ? Then why is it relevant to Descartes' demon and brain in a vat thought experiments? You'd have to say that these thought experiments are completely meaningless if the sensory apparatus that conveys info/data is, as you say, "not relevant". In fact the sensory apparatus, that it can be manipulated, is the cornerstone of these arguments/thought experiments.

Then why is it relevant to Descartes' demon and brain in a vat thought experiments? You'd have to say that these thought experiments are completely meaningless if the sensory apparatus that conveys info/data is, as you say, "not relevant". In fact the sensory apparatus, that it can be manipulated, is the cornerstone of these arguments/thought experiments. — TheMadFool

This might be the cornerstone of Descartes argument, but not Leibniz' principle. The identity of indiscernibles is a logical principle, not dependent on sensory apparatus. You are just conflating two distinct things in an incorrect way.

This might be the cornerstone of Descartes argument, but not Leibniz' principle. The identity of indiscernibles is a logical principle, not dependent on sensory apparatus. You are just conflating two distinct things in an incorrect way. — Metaphysician Undercover

I'm applying Leibniz to Descartes. There's nothing wrong with that, right?

Imagine a being discerns whether we're brains in vats or actual humans. Imagine also that this being is built like us and has a sensory apparatus that feeds it the information required to tell what we actually are. However, since this being too could be a brain in a vat for the same reason it's possible that we are or, if not, it could be an actual human being experiencing a complex hallucination.

The premise of your proposal is wrong. The brain in a vat scenario implies necessarily a 'person' who constructed the brain in a vat. This 'person' would discern the difference. So it is impossible that the two are indiscernible.

The premise of your proposal is wrong. The brain in a vat scenario implies necessarily a 'person' who constructed the brain in a vat. This 'person' would discern the difference. So it is impossible that the two are indiscernible. — Metaphysician Undercover

Ok. There's this person, call him X, who you say can discern whether we are brains in vats or actual human beings. However, it's still possible that X is one of us, a brain in a vat being fed false information or an actual human being having a hallucinatory episode.

The ability to know whether something is or is not a simulation is different from whether that something is a simulation — fdrake

I agree. I think @Pfhorrest made that amply clear and even @Metaphysician Undercover's thoughts align with this sentiment.

However, Descartes' and Gilbert Harman's (brain-in-vats) argument turns on precisely the "ability to know" the difference between the two worlds. Of course there's a discernible difference between being brains in vats and actual humam beings, it's self-explanatory, but the problem is that we can't know the difference.

the problem is that we can't know the difference — TheMadFool

Except we can, in principle; it’s just very very hard to get at that information.

Except we can, in principle; it’s just very very hard to get at that information. — Pfhorrest

I don't think we can for the reason that there must exist, as @Metaphysician Undercover posited, a being, call it X, that gets its hands on the information that can help it make the distinction but if X is anything like us the information must pass through a set-up of sensory apparatuses and then we're back to square one - this being could be just another one of us being fed false information of it could be an actual human being suffering from hallucinations.

Even if we’re not brains in vats, all of our experiences could conceivably be hallucinations. It is always possible to be radically skeptical to the point of solipsism or even complete nihilism, and once you’re there there is no argument that could reasonably convince you otherwise, because anyone making the argument or any evidence they present (or evidence that you find on your own) could all just be an illusion. That’s why such radical skepticism is not pragmatically warranted, and instead of justificationism like that (“I won’t believe anything until it can be proven from the ground up”), we must instead adopt critical rationalism (“I’ll believe whatever seems true until I find reasons to believe otherwise”). On a critical rationalist account, it is possible that we should have experiences that are inconsistent with the hypothesis that they originate from what we might falsely think is the natural world, and thought there are always infinitely many possible alternative hypotheses, the one that says we are brains in vats may seem far more likely, in which case we are warranted to believe it until we find evidence to the contrary.

Say, for example, that a human figure with apparent omnipotence appears to you out of thin air, tells you you’ve been a brain in a vat experiment, but the experiment is over now and they’re going to put your brain in a clone body, and let you join the real world. After discussing the whole thing at length you have a discontinuity in your experience and wake up in a different body in a different world. You live in the world for decades, a long fruitful life, but your clone body ages, and as you are on your death bed you are offered a chance to upload into a virtual reality that your brain in a vat experiment helped enable. You agree, and wake up in a beautiful world, in a young perfect body, and you can do stuff like fly and shoot fireballs from your hands with VR magic. You can also communicate with people’s in the world you’ve been experiencing for decades, and those people confirm that you are an uploaded mind in VR now. You continue living like that for thousands of years, keeping up on the news in the outside world too while you live in your virtual paradise.

What is more likely, which are you going to believe — that that experience is reflective of actual reality, and you really were a brain in a vat, or that you just had a millennia-long uninterrupted hallucination, or that there never was any reality to begin with, or something?

hat’s why such radical skepticism is not pragmatically warranted, and instead of justification like that (“I won’t believe anything until it can be proven from the ground up”), we must instead adopt critical rationalism (“I’ll believe whatever seems true until I find reasons to believe otherwise”). — Pfhorrest

That's sweeping the problem under the rug. You haven't dealt with the problem but decided to ignore it.

What is more likely, which are you going to believe — that that experience is reflective of actual reality, and you really were a brain in a vat, or that you just had a millennia-long uninterrupted hallucination, or that there never was any reality to begin with, or something? — Pfhorrest

Firstly, I don't think we can pin down a probability on which is more likely. I maybe wrong though and would like to hear your arguments if you have any. The heart of the issue is we're not certain which of the two scenarios is true.

That's sweeping the problem under the rug. You haven't dealt with the problem but decided to ignore it. — TheMadFool

No, I’ve concluded (like many before me) that it’s not a problem. “You don’t have good enough reason to think that” cannot be good enough reason to think otherwise, otherwise we end up in absurdity, forever rejecting everything, which is a great way to guarantee you never form correct beliefs. Critical rationalism is the only rational alternative.

However, it's still possible that X is one of us, a brain in a vat being fed false information or an actual human being having a hallucinatory episode. — TheMadFool

No, the brain in the vat premise implies that this is not possible. For us to be brains in vats, it is implied that someone created this situation. It is impossible that the person who created it was just hallucinating or else there would not be us, as brains in vats. You can understand this situation with dreams. It is possible that I am in a dream right now, but it is impossible that I am in someone else's dream.

I don't think we can for the reason that there must exist, as Metaphysician Undercover posited, a being, call it X, that gets its hands on the information that can help it make the distinction but if X is anything like us the information must pass through a set-up of sensory apparatuses and then we're back to square one - this being could be just another one of us being fed false information of it could be an actual human being suffering from hallucinations. — TheMadFool

It's not a matter of this person getting hands on the information, it's a matter of this person necessarily all ready knowing the difference (having the information) as prerequisite for the brain in vat scenario, being the intentional creator of the conditions. So you need to ask whether it's possible for the brain in vat scenario to exist without a creator. But the description, as brain in vat, implies that there is a creator. You could go to some other description, like "simulation hypothesis", but that also implies a creator.

I think it would be very difficult to come up with a compatible theory, which did not require a creator to create the proposed scenario. And if your scenario requires a creator, the creator has the necessary information. Also take notice that this information need not pass through sensory apparatus. When we create something, the idea for that thing, the plan, exists prior to the physical existence of that thing. So the creator dreams up the idea, figures out how to put the plan into action, and then does so, without ever having sensed the thing which is being created. An omniscient being (one which cannot be mistaken) can set up a time delayed scenario, leave the scene, and have all the information to know about what is going on in that scenario without ever sensing it.

No, I’ve concluded (like many before me) that it’s not a problem. “You don’t have good enough reason to think that” cannot be good enough reason to think otherwise, otherwise we end up in absurdity, forever rejecting everything, which is a great way to guarantee you never form correct beliefs. Critical rationalism is the only rational alternative. — Pfhorrest

I'm not saying that just because there's no good reason to think X it's ok to think Y or not X. All I'm saying is there's no good reason to think X.