Rick, I wonder if this is a British English rule.  As I mentioned, I found nothing about it in American English grammar books.  (Of course, I didn't find anything in them about "can not" a few weeks ago either!) 

We hear "grammar rules" and we think that grammar is a science.  Obviously, it isn't.  I recall three university professors who constantly argued about points of grammar.  Instead of "grammar rules", maybe we should be saying "grammar observations".  This is what I observed, and this is what I believe the rule to be.  Grammar seems to be more an art form than any science I can think of.

Back in the 1960s I remember being told that "ain't" was going to be accepted soon as correct English.  I think they were wrong.  In July I heard from professors at PUC using it, but the sound of the word hurt my ears.   I can't imagine an English teacher in the States accepting it as correct English.

Thanks for your time, Rick.  I appreciate it!

Dale