I could just as well ask why would I hallucinate anything. It was just an example that I used. So if I see two sticks next to each other:
Why can't the other one be a perfect hallucination and the other a physical stick?
It can, I suppose. The reason I didn't want to examine that example too closely is that I believe that "hallucination" in the way that you are using it - i.e. in it's general usage - makes the argument unclear. In it's philosophical usage - i.e. for the purposes of the argument from hallucination - then it has come to mean the brain in a vat situation because it is only in that situation where the argument from hallucination really bites. It's a slight redefinition of the word "hallucination". If you can claim either the brain is "malfunctioning" then P4 fails and if you are really misperceiving a different object then it becomes the argument from illusion. But I can try to use your example if you like.
I think P5 fails even in the case of the BIV. It has by definition perfect hallucinations of non-existent objects. Set up a stick and a videocamera. Feed the signal to the BIV. Now the BIV observes a physical object. You might disagree how direct the observation is but in my opinion the link from the physical object to the BIV is pretty straightforward. And the stick is definetly physical. Now it can have perfect hallucinations and see physical objects.
OK...I think I am understanding better. What you mean is that from the POV of the BIV "the stick is definately physical". It is indistinguishable from what it would call physical
if it wasn't a BIV. But that is the whole problem. According to one way of looking at it, the stick seems to be physical. But it isn't physical in the way we normally think of physical. You could put it like this: In the normal situation there is a real physical stick at the start of the causal chain but in the case of the BIV there is a computer at the start of the causal chain, but the end of the causal chain is the same in both cases. SO we have the same brain state, and the same experience, but two different ontological causes because the real stick and the BIV stick exist in different sorts of ways. So you
can have a perfect hallucination and you
can see physical objects. The point in your description where things start to go wrong is where you say "the stick is definately physical", because in a crucial sense we know that the stick definately
isn't physical. It is merely "represented" physically by a configuration of electrical charge inside the computers memory. It's not a physical stick at all. It is a "virtual" stick, which just appears to be physical. And that is why this is a problem for direct realism.
P5: Given this phenomenal indistinguishability, we have reason to suppose that, since the objects of immediate awareness in hallucination are not external physical objects, the objects of immediate awareness in veridical perception are also not external physical objects.
Your argument only works if the BIV is genuinely directly aware of a physical stick, but I don't think you can say that it is. You are actually challenging P2, not P5.
P2: . But no physical pink rats are present in the case of the drunk, and no physical dagger is present in the case of Macbeth, and no physical stick is present in the case of the BIV.
You want to claim P2 is false, but P2 is true - even for you - because virtual sticks in computer memory aren't physical sticks. The physical cause of the stick the BIV percieves is avtually a virtual stick.
Finally, and this is for
Krandal2 also, you are confusing direct realism with a sort of Kantian transcendental idealism. Krandal2 pointed out that in a certain respect the virtual stick exists in the way that Kant's noumena exists. Kant split the world into the phenomenal world - and that includes both what we call "mental" things
and the physical world as it manifests to us - and the noumenal world of "things in the themselves" - which we never have any access to. When you say that "the stick is physical" you don't mean it is physical. You mean it is
exists, in a noumenal sort of way. A direct realist believes that the stick he perceives
is the real physical stick. A transcendental idealist believes there is a "something" out there in the noumenal world which somehow corresponds to a physical stick, but that what we call "physical sticks" are just how things manifest to us. Do you see the difference now? In the normal case, there is no difference between the percieved stick and the real stick. In the case of the BIV the "real stick" is a pattern in a computer. So the first case would be direct realism and the second case would be transcendental idealism (i.e. non-realism with respect to the question originally asked in this poll). And the problem is that if you are going to be a transcendental idealist in the case of the BIV, then you ought to be a transcendental idealist in the normal case. Finally, the only way you can have your cake and eat it is to adopt disjunctivism and claim that even though the two cases are indistinguishable phenomenologically and neurologically they are in fact completely different things, and that is just very weird and very hard to justify.
As you said earlier perfect hallucinations are indistinguishable from physcical objects. So how could you know that nothing is physical if you see one or more perfect hallucinations?
This is not about "whether or not anything is physical". It is about what you
call "physical". Does "physical" refer to the
perceived things, like sticks, which manifest to you, or does it refer to "things as they are in themselves", regardless of how they manifest to you? Are these things the same thing? Direct realism claims they
are one and the same, and in the case of veridical experiences this is not a problem. But it
is a problem for the BIV because they are no longer one and the same. In the case of the BIV does "physical" refer to something percieved by the BIV, or to a pattern in a computers memory? It is hard to say these two things are the same thing.
Good.
That means you are thinking about it instead of just defending your knee-jerk assumptions and believing you understand the argument when you don't. And to be honest, I'm far from sure I understand it either. I am currently lucky enough to be studying this subject under one of the few people alive who have made an historically important contribution to this debate and I can tell you that most of his class are either well and truly confused or have given up hope completely.
