Re: SHOULD vs MUST

"Frank Ellermann" <nobody@xyzzy.claranet.de> Tue, 24 June 2008 21:27 UTC

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From: "Frank Ellermann" <nobody@xyzzy.claranet.de>
Subject: Re: SHOULD vs MUST
Date: Tue, 24 Jun 2008 23:28:50 +0200
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Dave Cridland wrote:
 
> A SHOULD X unless Y essentially means "SHOULD (X or Y)"

I'd read it as "do X, but if you have a very good excuse
not doing X might do.  One known very good excuse is Y."

OTOH for a MUST X I'd want no qualifiers, MUST means "an
attempt to do not X can cause havoc."  

This is also about a readability, I had a serious case of
DEnglish some days ago, an article was tagged with a note:

"This article may contain no original research".  I read
this as "apparently there is no original research in this
article", which would be perfectly fine wrt the linked
guideline.  Only much later it occured to me that I got
the "may ... not ..." wrong.  

If Y is the *only* possible very good excuse your version
"MUST X or Y, SHOULD X" is clear.  But SHOULD X often has
an implicitly known very good excuse:  Any older software
written before the SHOULD X was approved.

 Frank

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