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itself. Rather, my claim is that our phenomenal term seeing something red , the one
whose exercise involves instances or reactivations of our own red experiences, is not well
focused enough for it to be determinate whether or not the doppelganger's experience
falls under it. This term works well enough in discriminating normal human beings one
from another in respect of whether they are seeing something red. But when we seek to
apply the term beyond the cases where it normally works, it issues no definite answer.
In the normal human case, our phenomenal term seeing something red distinguishes
effectively between those who have both some physical property and a higher property
which is fixed by that physical property, and those who have neither of these properties.
But now we are asking the term to decide what we should say about a being who has the
higher property but not the physical property. There is no reason to suppose that there is
anything in the workings of the term to decide this question.
Again, we needn't suppose that there is anything less than definite in the doppelganger's
experience itself. For the doppelganger, the experience will feel as it does. The question
is rather whether an experience which feels like that is sufficiently similar to the normal
human experience of seeing something red to fall under our term seeing something red .
(Similarly, it might be indeterminate whether some experience induced by a
hallucinogenic drug, or produced by weird lighting, or deriving from the synaesthetic
appreciation of a sound, should count as seeing something red .)
Doubters are likely to remain unconvinced. They may feel that either the doppelganger's
experience is exactly like this colour experience (and here they imagine a red colour
experience), or it is not. Surely this must admit of a definite answer (for God at least,
even if the answer is not available to us).
But consider this analogy. Surely my friend's head of hair is exactly like mine in respect
of being bald, or it is not. Well, if my friend and I are strictly physically identical, then
surely we are alike in baldness. For it seems clear that, whatever baldness may refer to,
it must refer to some property that is fixed by strictly physical constitution. Two people
can't differ in being bald without differing physically.
Similarly, we can take it, two beings that are exactly identical physically must indeed be
alike in whether they are seeing something red , and for the same reason. Whatever
phenomenal concepts refer to, they must at least refer to something that is fixed by
strictly physical constitution, as was shown by the arguments in Chapter 1.
But now consider a friend whose hair is similar to mine in some ways, but not others.
Maybe he has the same number of hairs, in the same places, but his hair is of a different
texture or colour. Or maybe he has far fewer hairs, but they are somehow thicker than
mine. Now ask whether my friend's head of hair must be exactly like mine in respect of
being bald, or not. It is not clear. Bald is a vague term, and different refinements of the
term may issue in different verdicts on whether my friend is exactly as bald as I am. As
we use the term, there need be no fact of the matter as to whether we are exactly equally
bald.
Thus too, I say, with the doppelganger's visual experience. A being who is exactly like
me physically will indeed be just like me in respect of seeing something red. But there
need be no determinate answer for a being who shares some of my material properties but
not others. Different ways of refining the term seeing something red will issue in
different verdicts. So our actual unrefined use of the term fails to decide whether the
doppelganger is just like me in seeing something red, or not.
I can now deal with a query left hanging at the beginning of section 7.7: why can't we
assign a definite meaning to the silicon doppelganger's phenomenal reports? The
Wittgensteinian suspicion was that this is an unsurprising upshot of my misplaced
enthusiasm for private languages . However, we can now see that this isn't the reason at
all. Rather, the point is simply that the doppelganger's phenomenal terms are vague, just
as ours are, and for the same reason. Just as it is indefinite whether the phenomenal
concept that we express by seeing something red applies to the doppelganger's ripe
tomato experience, so it is indefinite whether the phenomenal concept that the
doppelganger so expresses applies to our ripe tomato experience.
end p.201
Let us take it that the doppelganger is like a human in all respects, historical and
contextual, bar its basic physical constitution. Then, just like us, it will have phenomenal
concepts, whose exercises incorporate its mental states or re-creations thereof, and which
thereby refer to those selfsame states. In particular, such a phenomenal concept will be
expressed by the doppelganger's words I am now seeing something red . This
phenomenal concept will pick out those doppelgangers who are looking at red things.
These doppelgangers will share a higher material property with humans, and this will be
realized by a silicate property which they do not so share. Now, does the doppelganger's
concept here refer to the material property or the silicate property? This will decide
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