John,
 
The terms restrictive and non-restrictive have both functional and syntactic uses.  Syntactically, a wh-rel preceded band perhaps followed by a pause is non-restrictive.  In formal written Engish, non-restrictives can't start with "that".  That-rels are exclusively restrictive.  In you second example, your interpretation that the clause does not restrict is correct, but the problem lies in what we consider restricting.  Since the lines were the only things on Mars that could be canals, adding who made them doesn't really restrict them further.  It does, however, define them more precisely, and that's another function of restrictives.
 
Herb

________________________________

From: Assembly for the Teaching of English Grammar on behalf of Crow, John T
Sent: Fri 11/26/2004 12:12 PM
To: [log in to unmask]
Subject: Restrictive Clauses



I just discovered a gap in my understanding of restrictive vs. non-restrictive clauses that I hope somebody can fill.  Here is the text that created the problem for me:

                Early astronomers, who considered Mars to be the best candidate for extraterrestrial life, thought they saw straight lines crisscrossing the planet.  They thought that the straight lines were irrigation canals that had to have been built by intelligent beings.

Clearly, the relative clause in the first sentence is non-restrictive.  However, the relative clause in the second sentence is also non-restrictive in that it does not help the reader to restrict or identify which irrigation canals the writer is discussing.  And yet my internal grammar clearly marks this one as being restrictive.  What am I missing??

Thanks,

John

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