Plenty of standards use shall, but never must, as their imperative word. For
example (the first standard I had to hand) ISO 27001 has many occurrences of
shall (not capitalised, that seems to be an IETF special) and none of must.
Shall is hard in English (outside standards). For a start there’s the
shall/will issue, see for example
http://www.oxforddictionaries.com/words/shall-or-will
(And where it says “In practice”, that may or may not be so if you have an
editor or a customer with strong views. Or hold such views yourself.)
But since standards are not written in the first person, when shall and will
are differentiated, from that link, shall is “a strong determination to do
something”. Not quite that same as a standardese instruction (unless we view it
as the strong determination of the instructor).
Which all is why RFC 2119 exists.
--
Christopher Dearlove
Senior Principal Engineer
BAE Systems Applied Intelligence Laboratories
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From: Ted Lemon [mailto:mellon(_at_)fugue(_dot_)com]
Sent: 11 August 2016 13:57
To: Stewart Bryant
Cc: Dearlove, Christopher (UK); Barry Leiba; IETF discussion list
Subject: Re: New Version Notification for draft-leiba-rfc2119-update-00.txt
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The problem with SHALL is that in other contexts it often means MUST, which is
kind of weird, and not really what the english word means. I tend to agree
that it's worth advising against its use.
On Thu, Aug 11, 2016 at 7:44 AM, Stewart Bryant
<stewart(_dot_)bryant(_at_)gmail(_dot_)com<mailto:stewart(_dot_)bryant(_at_)gmail(_dot_)com>>
wrote:
Optional is useful in a requirements RFC.
Feature x is REQUIRED
Feature y is OPTIONAL
- Stewart
On 11/08/2016 12:27, Dearlove, Christopher (UK) wrote:
Grammatically, RECOMMENDED is sometimes useful, as using SHOULD instead can
produce less clear sentences. In principal the same applies to OPTIONAL, but
I've never had cause to use it.
I wouldn't miss SHALL. Except that SHALL is often the word used outside the
IETF rather than must, and there may be many RFCs using it, so do need to keep
the explanation, even if deprecated to use it in new documents.
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