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Article 2933 of comp.ai.philosophy:
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>From: markrose@spss.com (Mark Rosenfelder)
Newsgroups: comp.ai.philosophy
Subject: Re: Table-lookup Chinese speaker
Message-ID: <1992Jan20.182835.5307@spss.com>
Date: 20 Jan 92 18:28:35 GMT
References: <1992Jan18.134742.4155@oracorp.com>
Organization: SPSS, Inc.
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Your replies don't address my point, which is that a table-lookup Chinese
speaker is IN PRINCIPLE impossible.

The mere fact of possessing a database of successful conversations does NOT
imply that the machine can itself pass the Turing test.  The basic problem
is that the machine's responses can be constrained to lie in the set of
successful conversations, but the human's cannot be.

Let's call the set of possible (up to hundred-year) conversations S.
Within S we enumerate as T the set of conversations we judge to have passed 
Turing Test.  It does not matter what criteria we use-- we can be as cautious
or as generous as we like.

Now picture a conversation C which fails the Turing test (that is, it's in
S but not in T).  We can represent C as s(0), s(1), s(2), ..., where these
are particular statements.

C is not in T, but initial sequences of C must exist in T.  For instance,
there must be a conversation which begins with statement s(0).  (If there
isn't, the machine immediately fails the Turing test, since you could stymie
it by beginning the conversation with s(0).)  Similarly, there is probably
a successful conversation which begins with s(0), s(1).  

There is some number m which is the highest number such that a conversation
beginning s(0), s(1), ... s(m) exists in T.  (m must be less than the total
length of the conversation, because we said that C was not in T.)

We can therefore have a conversation with the machine which starts with
s(0), s(1), ... all the way up to s(m).  The computer can utter s(m)
because it has in its table (that is in T) at least one conversation
(needless to say one besides C) which begins with this sequence.

However, we now utter s(m+1).  The machine now has no valid response to make.
There is no conversation in T which begins s(0), ... s(m), s(m+1), since m
is the *largest* number such that a conversation s(0), ..., s(m), ...
exists in T.  Since the machine has no response to make, it fails the
Turing test.


