So epistemologically, the BIV has no grounds for their position. — Marchesk

Physicalism can't be grounded in observation whether BIV or not. It's a matter of personal preference. Perhaps the BIV was very impressed by a physicalist professor. He feels dedicated to somehow uphold that view which seems conservative and somehow virtuous to him. The notion that the professor was just part of a program will be rejected due to this emotional bias.

If the BIV is a physicalist, it will confirm the reality of all the things it takes to be physical. It will rule out the possibility that it is a BIV because after all, Wittgenstein or Heidegger (or whoever), or some other poorly thought through explanation. It's really the above mentioned emotional attachment.

Or maybe it will take a more pragmatic approach and admit that it could be a BIV, but if it is, it can't do anything about it, so it may as well be a physicalist because that irritates its fictional mother-in-law.

An interesting question would be how the causality between mental and physical states could be upheld in the simulation. If a certain simulated state would result in a certain mental state one could dominate the state of the real world by reproducing the simulated state, which must result in a known mental state to uphold the simulation. Which means the vat would be forced to stimulate the brain in a certain way also.
Such things we call "Side-channel attack"

Physicalism can't be grounded in observation whether BIV or not. — frank

It can if one is a direct realist, because then you're perceiving the actual physical objects, instead of being aware of some mental intermediary.

What could you observe that would confirm or disconfirm either direct realism or physicalism?

If Mr BIV's scientific community concludes that the entire universe is a simulation being enjoyed by exactly one brain, and Mr BIV accepts that, then he's a physicalist in that his conclusion is in keeping with science, and he's also right.

However, it's also true that the vat and the brain are made up of physical stuff. — Marchesk

Is this part of the scenario? Or are you asserting it?

What could you observe that would confirm or disconfirm either direct realism or physicalism? — frank

We all make our philosophical arguments from some starting point, which will have some metaphysical basis. If one begins with there being a physical world that's directly perceived, then that rules out other problems that crop up with a different metaphysical starting point.

Is this part of the scenario? Or are you asserting it? — frank

I'm asserting that there is a BIV who espouses physicalism to explore whether there position could be consistent or defendable as a BIV, whether they realize their condition or not.

If Mr BIV's scientific community concludes that the entire universe is a simulation being enjoyed by exactly one brain, and Mr BIV accepts that, then he's a physicalist in that his conclusion is in keeping with science, and he's also right. — frank

Funny enough that brain would not be him.

We all make our philosophical arguments from some starting point, which will have some metaphysical basis. If one begins with there being a physical world that's directly perceived, then that rules out other problems that crop up with a different metaphysical starting point. — Marchesk

You're saying that we observe the avoidance of problems associated with other viewpoints, and this is observational support for direct realism. It's poor support because direct realism has problems of its own.

And we were talking about physicalism. Do you see that being identical to direct realism?

Funny enough that brain would not be him. — Heiko

No. He has a full life as a funeral director who is on the bomb squad for the local fire department. He's got three beautiful daughters, one of which is a drug addict. He's planning a trip to Antarctica in the fall. He's much more than a brain.

And we were talking about physicalism. Do you see that being identical to direct realism? — frank

Not at all, just that direct realism is a good epistemology for supporting physicalism.

You're saying that we observe the avoidance of problems associated with other viewpoints, and this is observational support for direct realism. — frank

I'm saying that we all start our philosophical arguments somewhere. And depending on where you start, there are certain considerations that fall out as a result.

I was just reading the SEP entry on solipsism for diversion, and early on a comment is made on how solipsism is a natural consequence of a certain view of the mind and epistemology. If you start out by saying the mind is necessarily independent from the body and knowledge begins with the subjective, then solipsism falls out from that sort of view.

And if being envatted is a possibility, then so is solipsism. There is a certain relatedness to these cartesian and ancient skeptical concerns.

The problem for the BIV is that their perceptions are not of a physical world, but a mental one constructed by the false sensory and bodily impressions the vat is feeding the brain. So epistemologically, the BIV has no grounds for their position. — Marchesk

They do have grounds. They have their empirical evidence. Problem is, you not given any clue as to the nature of the false reality being fed to this actual brain in a physical vat. If it is a story about a physical world, then the brain has grounds for their position. If on the other hand it is fed experience of a non-physical world, then it would have no empirical grounds.

However, it's also true that the vat and the brain are made up of physical stuff. So our BIV physicalist, while admitting they could be envatted, could argue that mental states are still physical.

Assuming you are a BIV is not a physicalist position. You seem to say this yourself:

It can if one is a direct realist, because then you're perceiving the actual physical objects, instead of being aware of some mental intermediary. — Marchesk

OK, you call it a direct realist here, but that is more or less the physicalist position: that what one perceives is the stuff that we're made of. The physics of the empirical reality being fed to the BIV would need to be capable of producing a conscious observer for physicalism to be a defensible position.

Let's say a person is actually a brain in a vat. They are convinced that physicalism is the case, which is to say that all of reality is made up of the stuff of physics without exception

How did this brain come to believe there is actually a physical world (a sine qua non for physicalism)? That is an essential question, because it has bearing on the rationality of its belief. In the real world, we believe there is a physical world because we interact with it (or so it seems, but it seems that way because of the way our perceptions are hardwired).

How did this brain come to believe there is actually a physical world (a sine qua non for physicalism)? That is an essential question, because it has bearing on the rationality of its belief. — Relativist

Because the vat is feeding them the sensory impressions of a physical world, similar to Neo in the Matrix.

OK, you call it a direct realist here, but that is more or less the physicalist position: that what one perceives is the stuff that we're made of. — noAxioms

Well, a scientific realist need not agree with direct perception. They can be an indirect realist, thinking that our perceptions of color, sound, etc. are illusions generated by the brain, and only the mathematical/physical descriptions are of real properties.

The physics of the empirical reality being fed to the BIV would need to be capable of producing a conscious observer for physicalism to be a defensible position. — noAxioms

This is a true, and that's a sticking point. On a Denettian position, it's difficult to see how being envatted and experiencing a fake physical world is possible. And in fact, Dennett has denied this is actually possible, because he doesn't think a computer program can handle the combinatorial explosion of interacting with a fake physical world.

I assume you mean false sensory impressions. In terms of formal epistemology, his belief in the physical world would be just as justified as ours, so this could also lead him to to justifiably infer physicalism - just as we could.

However, his belief in the physical world (and thus his belief in physicalism) would not constitute knowledge in the formal sense. That's because his belief is due to a Gettier condition (i.e. his belief is true by accident). Knowledge = a belief that is justified, true, and does not entail a Gettier problem.

Contrast this with our belief in the physical world. We believe there is such a thing because of our actual physical contact with it, through our innate capacity. Of course, we could be wrong - solipsism is possibly true (or you could be a brain in a vat who is imagining this conversation). That possibility just implies that our justified belief is actually false, and therefore doesn't constitute knowledge. But as long as our belief is true, we indeed have knowledge.

Physicalism can't be grounded in observation whether BIV or not

Yes and no. Our perception of the world (our mental interpretation of our sensory input) constitutes non-verbal beliefs, that are properly basic (they are innate, and are the product of nature to provide us a perceptual image that corresponds to some aspects of the actual world), about an external world and it's nature. This grounds our belief in a physical world. One can then infer the physical world to be all that exists (i.e physicalism).

That's a popular view, but it's not empirical verification of physicalism.

Are you saying this because physicalism can't be verified empirically (which isn't the same thing as being "grounded in observation") or because of something different about a BIV?

I agree physicalism can't be verified; neither can non-physicalist metaphysics. They are just theories, and all one can do is test their ability to account for aspects of the world, and potentially falsifying it by showing it incoherent.

What is the difference between "grounded in observation" and "empirically verified"?

I think we are all subject to “the vat”. That being societal constructs.

What is the difference between "grounded in observation" and "empirically verified"?

One can't empirically verify a negative (physicalism is the doctrine that no non-physical things exist). However, it may be reasonable to infer that only physical things exist because there's no evidence of anything else existing - that is still "grounded" in observation.

But lack of evidence is not evidence of lack, so that would be a pretty poor grounding.

On a Denettian position, it's difficult to see how being envatted and experiencing a fake physical world is possible. And in fact, Dennett has denied this is actually possible, because he doesn't think a computer program can handle the combinatorial explosion of interacting with a fake physical world. — Marchesk

It is pretty easy to disprove a literal brain (a pink biological thing like in the pictures) in a vat scenario. Everybody would have two brains, one in the vat (in charge) and one in the body (epiphenomenal). Somebody would notice the difference that signals from the body one are severed abruptly at some point in the brain stem to be replaced with uncaused signals controlling the motor functions.
Defects would be a distinguishing point. Bob has an aneurysm in the vat and displays the physical symptoms of that, but doctors find a brain with nothing wrong with it. Sue on the other hand has an aneurysm in the body brain, and yet continues to function normally, even after doctors notice the event (for whatever reason).

I think the BIV idea is not meant to be taken literally like this. It means an experiencer of complete unknown properties being fed experience of this world and this physics, but not being envatted in a similar world. Dennett is correct that our physics is not up to the task of running such a fake experience stream, but we know nothing of the limitations of the reality with the vat, so Dennett's denial is baseless.

BIV is a model of dualism, and all the evidence for or against it is evidence for or against the other.

The point I was making is that a BIV is in a nearly identical epistemic position as are we, except we know the BIV cannot have knowledge of the physical world, because his belief is a Gettier condition.

It's another matter about whether or not physicalism is a justified belief. The truism "absence of evidence is not evidence of absence" just means physicalism is possibly false- and without evidence, it is just a bare possibility, and the mere possibility of being wrong does not serve as a defeater for that belief. Compare this to solipsism -no one believes it's true despite the possibility it is false.

Have you noticed that the BIV scenario is a remake in scientific garb of the notion of a 'higher reality' beloved of religions everywhere? This vale of tears is but an illusion, and death will release us from it into this higher reality, controlled by the god of science. Talk of heaven and hell and the spirit world is dismissed as fantasy, but brains in vats...

True, but with a swerve that reflects our times. In the Matrix, life is boring and secure. Outside it there is blood and gore and grand purposes. Humanity struggles to survive in a quest against determinism itself.

Compare this with the traditional Baptist heaven which, as testified to by numerous hymns, is a place of pure rest. You can hear the exhaustion coming through in the lyrics. They just want to close their eyes and welcome sweet oblivion.

Earth as matrix, with heaven as the true reality would be a more coherent model. Instead of death being a sleep., it would be an awakening. I'll start writing hymns.

It is pretty easy to disprove a literal brain (a pink biological thing like in the pictures) in a vat scenario. Everybody would have two brains, one in the vat (in charge) and one in the body (epiphenomenal). Somebody would notice the difference that signals from the body one are severed abruptly at some point in the brain stem to be replaced with uncaused signals controlling the motor functions.
Defects would be a distinguishing point. Bob has an aneurysm in the vat and displays the physical symptoms of that, but doctors find a brain with nothing wrong with it. Sue on the other hand has an aneurysm in the body brain, and yet continues to function normally, even after doctors notice the event (for whatever reason). — noAxioms

This is a really good point that I had forgotten about. Same applies to the Matrix scenarios. One has to wonder what a brain operation inside the Matrix entailed from the patient, since there is only a plug into the back of the neck, and not the machines opening up pods and doing actual brain surgery. Or at least that was never shown in the movies, LOL.