Ian, you complicate things unnecessarily and it blurs the point.
1. You seem to agree with me that if (a really, really big IF, I know) you were a brain in a vat, you could not know for sure that you were one, ...
2. … since your experiences would be identical to what you would have experienced as a brain in a scull in a body in the real world.
Just answer yes or no for me, please.
I promise you, it relates directly to the solipsist and the reason David Mo said that all your arguments against it made no sense. Just bear with me, it
will make sense.
OK, if we are going to be entirely reasonable and constructive about this – I will try to give you an honest answer, and as far as possible without undue or biased influence from what has be said here before -
1. Re. The first highlight – I agree that if it was possible to put a disembodied but still living human brain in something called a “vat”, and possible to stimulate it with electrical or other signals which some other unknown intelligent being had created as a perfect way of causing that brain to have thoughts identical to what we experience as everything ever known in what we think of as the universe around us (that's a vastly detailed set of thoughts and thinking responses, that would fill billions upon trillions of A4 pages of description), then it is at least possible for us as not-brains-in-vats to make an un-evidenced unexplained proposal like that … though anyone could make countless such proposals about anything at all when they do not have to show any evidence or any credible explanation for what they are proposing.
IOW – the proposal seems to be this – if it were possible to produce a situation where you could not trust anything at all from any of your thoughts, then you could not trust anything at all from any of your thoughts. That's what the example of a BiV seems to boil down to. But that of course is a worthless statement of the sort that anyone could make about absolutely anything, unless of course they can show good evidence of how that could actually happen …
… but it's no use at all just saying “we cannot rule it out, because it MIGHT be possible” … anything
might be possible … that's a worthless statement unless you can show genuine evidence for how it
"might" be possible.
Here's a thought for you, which seems identical & equivalent to the BiV claim, only it's precisely the opposite way around -
- suppose the alien is completely wrong to believe that it has put a human brain in a vat, suppose instead that it is the advanced aliens brain which is actually the one in the vat! The alien brain has entirely false thoughts about what it imagines as a reality of putting a human brain in vat, and instead the actual reality is that real humans with a true reality are the ones who have put the alien brain into a vat of false unreal thoughts.
IOW – if you can request that we first assume that an alien intelligence could put a disembodied human brain in a vat, then we can equally request that you first assume that it was actually humans who had put the alien brain in a vat. So that its only the alien brain that has a false view of reality.
If you want me to show how it could be possible for humans to put an alien brain in a vat, then I want you to show
first how it could be possible for a supposed alien to put a human brain in a vat. You need to show that first, because it was entirely your claim in the first place!
2. Re. the second highlight – you are making an assumption that “your experiences would be identical “ to what you would have experienced as a brain in a real human body … but that's an unwarranted assumption and it's inadmissible until you can show how that could actually be the case. IOW if you build an argument based on any assumption like that, then you have to show that it would indeed be possible to produce literally “identical” thoughts to those which would occur if/when the same brain was functioning normally in a real human body in a real world of real events and real objects …
… IOW, you have to ask “is it actually a reasonable assumption to say that all thoughts would be identical?” … and the answer is that you have no idea lol! … at least you have no idea unless and until you can show good evidence for how that could be possible.
But to make a much more general observation – what I think is happening with all philosophical arguments like these (solipsism or Brain in Vat etc.), is that philosophers have merely created word-arguments that contain within their use of words & their phrasing, all sorts of hidden assumptions and semantic deceptions … so that at first sight the philosophical argument looks good … but it only looks good providing you accept all of the unspoken assumptions and premisses that are required to make that argument seem reasonable at all. But there is never any justification or actual evidence, or even a credible explanation offered to show why any of those unstated assumptions and unstated premisses are reasonable or likely to be true at all ….
… IOW what I suspect is happening in most philosophical arguments like this, is that the so-called “argument” really just reduces to a procedure of first getting everyone to accept a whole mass of unstated and unwarranted assumptions, and then claiming itself to be unassailable because you have already agreed to all it's unwarranted assumptions.
that philosophy has no answer to provide about understanding consciousness.