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From: debray@sbcs.UUCP
Newsgroups: net.ai
Subject: Re: Use of "and"
Message-ID: <640@sbcs.UUCP>
Date: Wed, 23-May-84 20:31:36 EDT
Article-I.D.: sbcs.640
Posted: Wed May 23 20:31:36 1984
Date-Received: Sat, 26-May-84 13:26:11 EDT
References: <3600002@iuvax.UUCP>
Organization: SUNY at Stony Brook
Lines: 47


	> No person would have any trouble at all understanding "people
	> in Indiana and Ohio", so why should a natural language parser
	> have trouble with it???

The problem is that the English word "and" is used in many different ways,
e.g.:

1) "The people in Indiana and Ohio" -- refers to the union of the set of
people in Indiana, and the set of people in Ohio.  Could conceivably be
rewritten as "the people in Indiana and the people in Ohio".  The arguments
to "and" can be reordered, i.e.  it refers to the same set as "the people in
Ohio and Indiana".  

2) "The house on 55th Street and 7th Avenue" -- refers to the *intersection*
of the set of houses on 55th street and the set of houses on 7th Avenue
(hopefully, a singleton set!).  NOT the same as "the house on 55th.  street
and the house on 7th.  Avenue".  The arguments to "and" *CAN* be reordered,
however, i.e.  one could as well say, "the house on 7th.  Ave.  and 55th
Street".  

3) "You can log on to the computer and post an article to the net" -- refers
to a temporal order of events: login, THEN post to the net.  Again, not the
same as "you can log on to the computer and you can post an article to the
net".  Unlike (2) above, the meaning changes if the arguments to "and" are
reordered.  

4) "John aced Physics and Math" -- refers to logical conjunction.  Differs
from (2) in that it can also be rewritten as "John aced Physics and John
aced Math".

&c.

People know how to parse these different uses of "and" correctly due to a
wealth of semantic knowledge.  For example, knowledge about computers (that
articles cannot be posted to the net without logging onto a computer)
enables us to determine that the "and" in (3) above refers to a temporal
ordering of events.  Without such semantic information, your English
parser'll probably get into trouble.  
-- 
Saumya Debray, 	SUNY at Stony Brook

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