question about Putnam's argument against BIVs

Let me ask a question on Putnam’s anti-skeptical argument against the possibility that we are BIVs (Brains In Vats). Here’s the argument (from class.uidaho.edu/morourke/44 … ticism.htm)

The question I have is this: if the phrase “we are BIVs” can only refer to the “image”, then does the Putnam argument presuppose some kind of a subjectivist or idealist position whereby the world just is our sense data?

No.

plato.stanford.edu/entries/brain-vat/

en.wikipedia.org/wiki/Semantic_externalism

Do those help?

He is just saying that you can’t meaningfully make a statement about something you can’t experience. Whether or not we are, in fact, BIV, we could never know what it is to be a BIV since that is not how we experience the world. So we can’t truthfully say that we are BIVs (even if we are), because we have no way to access that condition.

THe purpose of BIV is to be a skeptical device. I don’t think anyone sees it as a viable ontological position. But if anyone did, then this argument presents a pretty big problem for them.

I think he’s working off Hume’s test for significance. Basically just saying that a term has significance (that it should be considered) only when the term has a basis in experience. And it does seem to me that this supposes representative realism.

I’ll read those articles when I have more time (perhaps this evening), but let me just pursue this further now.

Putnam seems to be saying more than just that we can’t say “We’re BIVs” in virtue of our isolation from our invatted state. He seems to be saying that all our statements refer only to things in “the image”. His argument depends on this. Essentially, he seems to be saying that “the world” or “reality” can only mean something if it refers to our experiences. That’s subjectivism.

I don’t understand how this is an anti-skeptical argument. Wouldn’t the skeptic proposing that we might be brains in vats already know that we can’t say for sure whether or not we are? In fact, wouldn’t that be his whole point? This argument would refute somebody who said “We are definitely brains in vats”, but that’s not a skeptic, that’s a jackass!

Thats kind of exactly what I said.

Right! And the only way to escape that is to posit some form of subjectivism or idealism in which case “the world” refers only to our sense data. This is what I’m confused about (hopefully Xunzian’s articles will shed some light on it).

All right, I read the articles and I think this is what we’re missing:

So the Putnam argument doesn’t presuppose subjectivism or idealism (or anything of that variety) because ‘trees’ (or BIVs) can refer to the signals being inputted into the brain or to the computer program inputting those signals.

Of course, it still relies on semantic externalism, which I still disagree with, but that’s another matter.

Ucci,

I’d disagree. The skeptic can always posit an ‘evil demon’ or that we are ‘BIVs’ or whatever . . . I mean, we can’t really “know” can we? Well, the BIV argument shows that such pondering is absolutely worthless. An unknowable state is just that, unknowable. It doesn’t affect us in any meaningful way at all. So why should we entertain its truth-value? Even if it were true, it changes nothing.

Isn’t that basically what pragmatism says?

That would follow, what with Putnam being a pragmatist.