The brain-in-a-vat and other such hypotheses are just analogies. The underlying principle is best exemplified by Kant's transcendental idealism. There is indeed something that is the cause of experience, but given the logical possibility of such things as the brain-in-a-vat hypothesis, it is not a given that everyday experiences show us the cause of experience. The causal world might be very unlike what is seen. And that includes being very unlike the material world as is understood in modern physics. So it's not that we could just be some brain-in-a-vat, it's that we could just be some conscious thing in some otherwise ineffable noumena.

At the very least this might warrant skepticism (in the weaker sense of understanding that we might be wrong, not in the stronger sense of believing that we're likely wrong). — Michael

Just because we can imagine something does not mean it is possible.

Lets suppose one day a scientist demonstrates that the "brain-in-a-vat" is not possible due to the "Laws of Nature".

What would be the skeptic's reaction? Well, they could just say, "it could just be another scientist manipulating a "brain-in-a-vat" to think it is not physical possible to create a "brain-in-a-vat" due to the "Laws of Nature".

What are you going to believe? Someone's imagination(hypothesis), or someone's demonstration by theory and experiment that such an idea from someone's imagination(hypothesis) is not possible.

At times, the empirical needs to set the boundaries for the creative mind.

There is indeed something that is the cause of experience, but given the logical possibility of such things as the brain-in-a-vat hypothesis, it is not a given that everyday experiences show us the cause of experience. The causal world might be very unlike what is seen. — Michael

Kant has a lot to answer for.

The hypothesis is that what we see might be totally different to a conjectured, inaccessible world about which we can say nothing.

Let's think on that for a bit.

If this world is inaccessible, and if we can say nothing about it, then how could it be the cause of what we do see? And if it is the cause of what we do see, then we can talk about it, hence it is not inaccessible.

Kant was working in a time when microscopes were a novelty, a time prior to the discovery of sodium and potassium, before electrochemistry, before Dalton's Law of Multiple Proportions, before electrons. After his death, we began to work out what was going on behind the scenes, in ways that Kant did not imagine. We accessed what Kant had taken to be an inaccessible world.

I suspect that if we could bring Kant back and show him what happened over the hundred years after his death, he'd just say "well, I go that wrong".

There are two philosophical points here. The first is that, since the "unseen" world causes what we see, we can and have used those causes to grasp the nature of that unseen world. Science did what Kant imagined to be impossible.

The second philosophical point imagines a Kantian chauvinist, who makes the claim that these scientific advances do not show us this invisible world; that by definition the supposed "actual" world still lies outside our ken. The reply to him is simply that since such a world is utterly outside of what we can comprehend, it cannot act as the cause of what we experience. Such a world drops out of our considerations.

One can't have it both ways, supposing that the hypothesised unseen world both causes what we see and yet remains outside of our considerations.

This applies to the vatted brain. Should one hypothesis that what one sees is an illusion, one thereby hypothesises a meta-world, a world in which the illusion may take place. For the vatted brain, this is the vat; for Neo, his pod. What one cannot conclude is that everything is an illusion.

If the phenomenalist supposes that we cannot deduce from our perceptions what the world is like, he has been shown to be mistaken. If the phenomenalist supposes that we cannot say anything about how the world actually is, his view is utterly irrelevant.

the kind of thing that we hear in the case of a veridical perception is the same kind of thing that we hear in the case of an hallucinatory perception — Michael

But we are able to recognise hallucinations. Hence the kind of thing that we hear in the case of a veridical perception is not the same kind of thing that we hear in the case of an hallucinatory perception.

That is, as the SEP article points out, the common kind claim fails.

Recall the scene in A Beautiful Mind where Nash asks a passing stranger if they can see the representative from the Nobel Foundation.

The ability to tell the difference can be taken off line with drugs. Datura is one.

Recall the scene in A Beautiful Mind where Nash asks a passing stranger if they can see the representative from the Nobel Foundation. — Banno

Ketamine is another.

It has to be spelled out? We recognise illusion and hallucination in virtue of being a member of a community.

has to be spelled out? We recognise illusion and hallucination in virtue of being a member of a community. — Banno

If you were on Ketamine you wouldn't be able to tell that you were hallucinating and if someone tried to tell you, you wouldn't believe them.

There are times when there's no difference.

And...?

Hence, Phenomenalism?

Hence your claim that hallucinations are not the same kind of thing as normal experience is wrong.

So we have no way of telling if someone is on Ketamine?

So we have no way of telling if someone is on Ketamine? — Banno

Why is that significant?

Do you have some argument? Then present it. I'm not doing your work for you.

My suspicion is that when you try to put your argument sequentially, you will find that it was an illusion.

Thus, a veridical, illusory, and hallucinatory experience, all alike in being experiences (as) of a churchyard covered in white snow, are not merely superficially similar, they are fundamentally the same: these experiences have the same nature, fundamentally the same kind of experiential event is occurring in each case.

I don't think this is justified. If I dream of a churchyard covered in snow I cannot decide to move around it, walk up to and touch its cold wet stones, turn my back on it and see the surrounding landscape, look up and see the grey dismal skies and then turn back and see the church looking just as it did when I first looked at it. In any case that has been my experience at least, with dream imagery and drug experiences where I have been able to tell the difference when moved to do so, which is the closest I have ever come to having such a realistic hallucination. So, in my experience at least, it is certainly not the same kind of experiential event occurring in each case.

If you were on Ketamine you wouldn't be able to tell that you were hallucinating and if someone tried to tell you, you wouldn't believe them. — Tate

I have had extensive experience with psilocybin, LSD, DMT. mescaline and salvinorin, although not with ketamine. What you claim has not been my experience, however powerful the hallucinatory experience has been, if I have had the presence of mind to test it in the way I outlined with the 'churchyard' example I have always been able to tell the difference. On the other hand if one becomes absorbed by, lost in, the hallucination there is no thought of doing such testing which makes the claim moot.

Do you have personal experience to back up your claims about ketamine or are you relying on hearsay? If it is personal experience, did you have the presence of mind to test whether you were hallucinating in the kind of way I outlined?

Thus, a veridical, illusory, and hallucinatory experience, all alike in being experiences (as) of a churchyard covered in white snow, are not merely superficially similar, they are fundamentally the same: these experiences have the same nature, fundamentally the same kind of experiential event is occurring in each case. Any differences between them are external to their nature as experiences (e.g., to do with how they are caused).

I would not agree these ever could be the same kind of experiential event. An hallucinatory experience is private to the subject. There is no verification of a subject's hallucinatory reporting, while a veridical experience can in principle be verified since they can report on a public environment.

I do not know how in principle you can make a claim that they a fundamentally the same. How is this comparison to see if in fact they are exactly the same done? Ask the person to describe their hallucination? By seeing how detailed they speak of it? But what if they talk about a book they never read, and I ask him to open it to read page ##. Would they be able to do it? And how do I verify they get it right? If I ask them to examine their hallucinated Plato's Republic which they never read, could they get the passages right?

Yep.

The common kind claim, that hallucination or dreams are of the same kind as our seeing a tree or a cup, seems to involve a mild form of solipsism, along the lines of that if it seems real to me alone, then it is real. That's the problem with 's contention.

We recognise illusion and hallucination in virtue of being a member of a community. — Banno

The indirect realist’s claim just amounts to the claim that when reading about history we’re just reading words, which is true. — Michael

You made a further claim about what does inform our intellectual considerations. You did not merely claim that the external object does not inform our intellectual considerations directly. You made the claim that it does not tout court, and that something else does.

I don't think this is justified. If I dream of a churchyard covered in snow I cannot decide to move around it, walk up to and touch its cold wet stones, turn my back on it and see the surrounding landscape, look up and see the grey dismal skies and then turn back and see the church looking just as it did when I first looked at it. — Janus

So we have no way of telling if someone is on Ketamine? — Banno

These are absolutely spot on. It's how the problem is solved in active inference, it's the active part.

Inference (perception in this case) is an active process. We do not passively receive data from the external world, we actively sample it. From saccades in perception, all the way up to the construction of a skyscraper (which matches our image of the skyscraper we intended to be there). There's no active inference without interaction. If you can't sample your image, can't move you eyes around it, reach out to it, give part of it to someone else, drink from the cup in it and feel that in your stomach... then you're not perceiving it, you're hallucinating it, or dreaming it.

The fact that hallucinations and dreams both make use of a part of the system of perception is interesting scientifically, and has yield some really good research (not to mention a few promising therapies for mental illness) but is has no bearing on the question of what we see, it is related to the question of how we see.

Berkeley already answered the indirect realist critique of phenomenalism almost 340 years ago, e.g

"we may say that my gray idea of the cherry, formed in dim light, is not in itself wrong and forms a part of the bundle-object just as much as your red idea, formed in daylight. However, if I judge that the cherry would look gray in bright light, I’m in error. Furthermore, following Berkeley’s directive to speak with the vulgar, I ought not to say (in ordinary circumstances) that “the cherry is gray,” since that will be taken to imply that the cherry would look gray to humans in daylight."

Berkeley grammatically rule out indirect realism in his constructive logic of perception via his so-called "master argument" , that amounts to defining the meaning of an 'unperceived object ' in terms of present acts of cognition in combination with immediate sense-data.

His uniform treatment of the cases of veridical perception and non-veridical perception as both pertaining to immediate ideas, implies that for Berkeley "reality" means coherence of thought and perception.

You made a further claim about what does inform our intellectual considerations. You did not merely claim that the external object does not inform our intellectual considerations directly. You made the claim that it does not tout court, and that something else does. — Isaac

Yes. Just like it is not history that informs us about history but the words written in the textbook that do. But it’s still about history.

it is not history that informs us about history but the words written in the textbook that do. But it’s still about history. — Michael

Why?

Recall the scene in A Beautiful Mind where Nash asks a passing stranger if they can see the representative from the Nobel Foundation. — Banno

I would not agree these ever could be the same kind of experiential event. An hallucinatory experience is private to the subject. There is no verification of a subject's hallucinatory reporting, while a veridical experience can in principle be verified since they can report on a public environment. — Richard B

From the SEP article:

The argument from hallucination relies on the possibility of hallucinations as understood above. Such hallucinations are not like real drug-induced hallucinations or hallucinations suffered by those with certain mental disorders. They are rather supposed to be merely possible events. For example, suppose you are now having a veridical perception of a snow-covered churchyard. The assumption that hallucinations are possible means that you could have an experience which is subjectively indistinguishable—that is, indistinguishable by you, “from the inside”—from a veridical perception of a snow-covered churchyard, but where there is in fact no churchyard presented or there to be perceived.

…

However, as noted above, from a phenomenological point of view, hallucinations too seem as though they are direct presentations of ordinary objects: from the subject’s perspective a hallucination as of an F cannot be distinguished from a veridical experience of an F. This is why it seems so plausible to think of them as fundamentally the same.

That we can determine whether or not an experience is an hallucination by trying to verify them with other people has no bearing on the Common Kind Claim.

And to take it out of the hypothetical and into what actually happens; the schizophrenic hears voices and these voices are just “in the head”, and so the indirect realist’s general claim that there is something like “sense data” that can be the direct object of perception should be understandable. They just claim that this is what happens in the case of a veridical perception as well. Veridical perceptions just differ in that they have some shared external cause that causes the same kind of experience in other people. And so, again, your objections here do not undermine, or even address, the indirect realist’s claim.

There are two philosophical points here. The first is that, since the "unseen" world causes what we see, we can and have used those causes to grasp the nature of that unseen world. Science did what Kant imagined to be impossible. — Banno

Scientific realism isn’t a given, and even if it were true, the world as described by the Standard Model is very unlike the world as seen in everyday experience, and so something like Kant’s transcendental idealism (just less extreme) is suggested. This is the position I tend to take.

The reply to him is simply that since such a world is utterly outside of what we can comprehend, it cannot act as the cause of what we experience. — Banno

That doesn’t follow. A dog cannot comprehend the physical causes of his experiences but his experiences nonetheless are caused by these physical things. We don’t need to be able to make sense of some cause for it to be a cause.

Why? — Isaac

"Why is it the words and not the events that inform us?" ?

Or "why are the words still about the events?" ?

There are two philosophical points here. The first is that, since the "unseen" world causes what we see, we can and have used those causes to grasp the nature of that unseen world. Science did what Kant imagined to be impossible. — Banno

Yup. Effects, like a visual experiences, carry information about their causes, like the object and the light reflected off the object and into your eye. Information is the relationship between cause and effect.

Scientific realism isn’t a given, and even if it were true, the world as described by the Standard Model is very unlike the world as seen in everyday experience, — Michael

How do we know the difference between our experience of the world and the way the world is independent of our experience? You must have had some experience to even make this claim, so there must be some experience that has informed you how the world is independent if your experience. Or your experience is sufficient to know how the world is independent of your own experience. There must be something in your experience that informs you of how the world is unlike your experience, but how could that be if not by some experience?

Seems to me that you've misused language.

How do we know the difference between our experience of the world and the way the world is independent of our experience? You must have had some experience to even make this claim, so there must be some experience that has informed you how the world is independent if your experience. — Harry Hindu

My experience doesn’t show me the nature of the world independent of experience, the Standard Model and other scientific theories do.

Suppose that you begin to question whether you are awake or dreaming and conclude that you are awake. Then suppose that a while later you experience 'waking up' and conclude that your earlier self was dreaming. Does this mean that your earlier self's beliefs were wrong during the course of the previous dream, or does this only mean that your earlier self is presently wrong in relation to your present observation of 'waking up' ? Then recall the phenomena of false awakenings...

In other words, when judging the veracity of a perception, does the verdict only hold at the time of the verdict?

"Why is it the words and not the events that inform us?" ?

Or "why are the words still about the events?" ? — bongo fury

The former.

There seems to be chain of causality - events -> (various perception processes) -> (various executive process) -> writing words to convey the events -> looking at words conveying the event -> (various perception processes) -> (various linguistic process) -> (various executive processes) -> (working memory storage) -> (more executive functions and long term memory processes - collectively called 'learning').

There seems a lot of stages between words and learning, so if stages between is what leads to the charge of indirectness, then the we indirectly learn from the words too.

Does this mean that your earlier self's beliefs were wrong during the course of the previous dream, or does this only mean that your earlier self is presently wrong in relation to your present observation of 'waking up' ? — sime

One of a suite of reasons why beliefs in cognitive science are often treated as 'propensities to act as if...'

Your dreaming self has no propensity to act as if you were awake, so it has no belief that you are awake. It's merely rehearsing some of the neural processes that having such a belief would use.