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Article 2789 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: <1992Jan16.180846.7095@spss.com>
Date: 16 Jan 92 18:08:46 GMT
References: <1992Jan15.181213.29101@oracorp.com>
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In article <1992Jan15.181213.29101@oracorp.com> daryl@oracorp.com writes:
>I thought that it would be uncontroversial. By whatever criterion you
>use for "sensible conversations", the fact that the conversations are
>only finite in length immediately implies that there exists a finite
>state machine that has only sensible conversations. 

Perhaps the troubling concept here is the idea that the set of "sensible
conversations" can be specified at all.  Would you maintain that the
set of possible propositions could be divided into true and false ones,
and a table-lookup machine programmed to produce only true statements?
One would soon run into paradoxes, such as assigning the correct truth
value to statements like "There are precisely 10^2400 true statements in
the database", whose truth value depends precisely on what truth values
are assigned to other statements.  The concept of a "sensible conversation"
might be similarly slippery.

But let's pretend that the database of "conversations which pass the Turing
test" can be specified and does exist.  It does NOT follow that a table
lookup machine randomly choosing conversations from this database
will itself pass the Turing test.  This is easily demonstrated.

Suppose you start the conversation with "Hello".  The computer responds
with "Hello, Professor Chung!"  It can say this because there is in fact
a successful Turing-conversation in the database which begins this way--
it's a conversation with Prof. Chung, naturally.  

Your next reply is "Huh?"  And the computer explodes, because it finds
it HAS NO CONVERSATIONS which begin with these three sentences.  The
successful conversation it used last time proceeded in a different way.
  
You can restrict the database as narrowly as you want (say "conversations
with Daryl McCullough which pass the Turing test") without avoiding the
problem.  There must exist some conversation C in the database, which
is the ONLY conversation which begins with the sequence s1, s2, ... sn,
where these are particular statements.  (This claim must be true if the
database is finite.)

The computer has just uttered statement sn.  If you utter statement s(n+1),
all is well-- the computer can still proceed with conversation C.
But if you utter any other statement, (e.g. t) it has failed the Turing test,
because it has no entry in the database of passing conversations which
begins with s1, s2, ..., sn, t.

(To avoid red herrings, I am using "conversation" as you do, to mean 
a life-long interaction; only one of the set of conversations of Daryl
McCullough could therefore be instantiated.  This does not change the
argument any.)


