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From: dave@tygra.Michigan.COM (David Conrad)
Newsgroups: comp.ai.philosophy
Subject: Re: UNIFIED MODEL FOR KNOWLEDGE REPRESENTATION? (IMPOSSIBLE
Message-ID: <1991Jun16.083632.1383@tygra.Michigan.COM>
Date: 16 Jun 91 08:36:32 GMT
References: <25348@samsung.samsung.com> <8455@awdprime.UUCP>
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In article <8455@awdprime.UUCP> sjb@piobe.austin.ibm.com writes:
>
>... the question proposed was "How, then, can any two
>speakers know that they are speaking about the same thing?"
>
>How, indeed?  This is a VERY fundamental philosophical question...
>
>[Much about only knowing that which is perceived]
>
>Scott

Bertrand Russell has a fascinating discussion of all this in his book
_The_Problems_of_Philosophy_.  He concludes that we cannot know anything
about objects in the world directly, but only indirectly.  The only things
we can have direct knowledge of are our sensations.   Our knowledge of
objects must always be indirect.  Actually, in addition to our perceptions
we are also directly aware of abstract concepts, which Russell terms
'Universals'.  E.g. I am aware of my sensation of seeing this keyboard
in front of me, and touching it, and hearing the keys click, but I cannot
be *aware* of the existance of the keyboard; I can only infer its existance.
Should I believe that it exists?  Or should I believe it to be a figment of
my imagination?  (I.e. Objective Reality vs. Solipsism.)  Russell concludes
that the consistency of our observations (the keyboard is there *every* time
I look; things simply do not vanish into (or appear from) thin air) suggests
that we should choose, with Occam's razor, to believe that there is indeed
an objective reality, even though we can never experience it directly.

Additionally, we are aware of universals, such as '1+1=2'.  There is no
greater knowledge of it attainable than that which the mind apprehends
immediately.  To use an example which was brought up before, we may doubt
that Bogota is actually the capital of Columbia, or that there is even a
city named Bogota, and we might seek to go to Columbia to see the city for
ourselves.  (We would still have no direct knowledge of Bogota, but our own
sensory perceptions are presumably more trustworthy than our perceptions of
the writing which is supposed to record the sensory observations of persons
not personally known to us.)  But what on earth could it mean to "go and
see the *real* '1+1=2'"?

Back to the question of how two people can know if they are talking about
the same thing, let us take a simple sentence, "There is a man named David
Conrad."  This statement is very different for different people.  I have
direct knowledge of David Conrad.  I am the only person in the universe, 
in fact, who *knows* that the statement is true.  Those with whom I am
acquainted only know of their perceptions of me, from which they infer my
existance.  Most of the rest of you only know of me by description (using
the word 'description' to mean any knowledge gained by language and not
by sensory perception of the object).  So is the sentence the same?
Does it even refer to the same person?  What if you were to discuss this
article with someone, and they were to say, "Oh, I know a David Conrad,"
but it turned out that they only knew someone of the same name?

I think that all that can be said is that a person may think that another
person's description of sensations is consistent with the first persons
sensations, and thus may have been caused by the same object.  When more
information becomes available, either through additional sensations, or
a more specific description of the other's sensations, then the identity
may be reconsidered, either reinforced if the similarity persists, or
dispelled if there is a disagreement ("Oh, the sign was green?  Must have
been a different one than the one I saw, then.").  Knowledge that the
two are referring to the same object must therefore always remain
problematic.  Indeed, it is not possible to say for certain that the
other person even exists.  So the question becomes, "What factors are
used in deciding if a description matches our sensations (or memories
of sensations)."

(I forgot to mention that our memories are also things of which we are
directly aware.  In fact I haven't done justice at all to Russell's
argument, and I suggest anyone who is interested get a copy of
_The_Problems_of_Philosophy_ and read his arguments first hand.)

David R. Conrad
dave@michigan.com
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