I'm writing a rather tehnical report with a lot of abbreviations such as QoS (quality of service), AES (Advanced Encryption Standard) and HMAC (Hash-based Message Authentication Code).

When should the explanation of the abbreviation be capitalized? For example, should it be quality of service or Quality of Service? How does one know what to use for the vast majority of technical abbreviations?


According to the Wikipedia Manual of Style, these are some rules on the matter (I'll paste it):

When showing the source of an acronym, initialism, or syllabic abbreviation, emphasizing the letters that make up the acronym is undesirable:

Incorrect: FOREX (FOReign EXchange)
Incorrect: FOREX (foreign exchange)
Correct: FOREX (foreign exchange)

If it is necessary to do so, for example, to indicate the etymology, use italics: FOREX (from "foreign exchange")

Specifically, do not apply initial capitals in a full term that is a common noun just because capitals are used in the abbreviation.

Incorrect (not a name/proper noun): We used Digital Scanning (DS) technology
Correct: We used digital scanning (DS) technology
Correct (name/proper noun): produced by the British Broadcasting Corporation (BBC)

So: don't capitalize if the words are "common" and capitalize if the acronym refers to proper names. See also page 81 in this document.

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    Strictly speaking, this is Wikipedia 's Manual of Style rule on showing the source of an abbreviation. There's no mention on when or how to capitalise abbreviations. – Hugo Sep 2 '11 at 13:03
  • @Hugo: There is no need for that to be mentioned, since the OP asked how should we capitalise the source of an abbreviation and not the abbreviation itself. He wrote "What I can't seem to grasp is when should the explanation of the abbreviation be capitalized?". I think this answer explains that. – Alenanno Sep 2 '11 at 13:33
  • @Alenanno Oops, I misread the question and therefore that Wikipedia text is a good example. Thanks! – Hugo Sep 2 '11 at 13:52
  • @Hugo: No problem! :) – Alenanno Sep 2 '11 at 13:53
  • Why is Wikipedia's manual of style authoritative? Seems an odd source to quote. – herisson Sep 30 '15 at 18:25

A simple question with a complicated answer. First of all, the abbreviations you mention are actually called acronyms, i.e. words that are composed of parts of several words. An abbreviation, on the other hand, stands only for a single word.

As for the actual answer:

Here are some rules I can think of that govern the capitalization of the letters in an acronym:

  • "QoS" is about "Quality" and about "Service", the "of" only serves to connect those two. So to mark the "of" as not so important, it is lower case.

  • Letters in an acronym can also be mixed case when one partial word contributes more than 1 letter to the acronym, and is therefore in lowercase so as not to imply that there are more words. Example: BVerfG stands for Bundes-Verfassungs-Gericht, the highest German court (can't think of a quick example in English)

  • Acronyms can also turn into regular words with regular capitalization, if they are pronouncable as regular words, and if they come into common usage. Example: "Laser" comes from "LASER" (Light Amplification through Stimulated Emmission of Radiation)
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    Where is the actual answer? The question isn't about capitalisation of acronyms themselves, but whether you should retain the capitals if you write the expanded form. – z7sg Ѫ Sep 2 '11 at 14:20

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