Subject: Re: "Be liberal..."

From: [email-masked]
Date: Mon, 1 Nov 1999 12:05:12 -0800

*> From [email-masked] Sun Oct 31 17:32:53 1999
  *> Date: Sun, 31 Oct 1999 19:32:50 -0600 (CST)
  *> From: Tim Salo <[email-masked]>
  *> To: [email-masked]
  *> Subject: "Be liberal..."
  *> Content-Length: 925
  *> X-Lines: 28
  *> 
  *> Bob Braden,
  *> 
  *> It seems like I should know the answer to this, but...
  *> 
  *> In RFC 1122 you quote Jon Postel as saying:
  *> 
  *> 	"Be liberal in what you accept, and
  *>         conservative in what you send"
  *> 
  *> However, in RFC 791 Jon Postel actually said:
  *> 
  *> 	"In general, an implementation must be conservative
  *>         in its sending behavior, and liberal in its receiving behavior."
  *> 
  *> I can't find the RFC 1122 quote in RFC 791.  The RFC 1122 language is
  *> the form that is usually attributed to Jon Postel, but it appears to me
  *> that this may be either your summary of Jon's words or perhaps quoting
  *> Jon's spoken, rather than written, words.
  *> 
  *> Do you have any suggestions about how to best reference "Be liberal..."
  *> I would like to quote a document edited by Jon, (without intending
  *> any disrespect for your editorial abilities and accomplishments...).
  *> Or, are you actually the author of the more concise version of "Be
  *> liberal..."?
  *> 
  *> Thanks,
  *> 
  *> 	-tjs
  *> 

Tim,

I am taking the liberty of CCing this message to the ietf list, since
the question has arisen several times recently and maybe I can answer it
once for all.

First of all, the two quotes above are (intended to be) semantically
equivalent.  Jon was fond of stating the idea, and those involved in
the ARPAnet and early Internet research were familiar with his
statements.  The two quotes do differ in style; the RFC 1122 quote was
intended to be closer to what Jon actually SAID, while the RFC 791
version was couched in more formal written language.  At the time RFC
1122 was published, I checked out the quote with Jon, and he was happy
with the shorter form.  So either quotation is "authorized".

I have recently seen a version that goes something like, "Be
conservative in what you do and liberal in what you accept".  It seems
to me this is not semantically equivalent to the quotes above, since it
apparently extends the principle beyond its specific domain of protocol
packets into some sort of philosophical doctrine about life and
people.  I believe that Jon would not have sanctioned such a liberal
interpretation.

Bob Braden