How to capitalize (or not) an abbreviation, is there any rule?

Reading this article I was quite puzzled about the way the author capitalized or not the abbreviations.

When writing in full:

The Internet Corporation for Assigned Names and Number

All words are capitalized, but when abbreviating only the first letter is capitalized:

The Internet Corporation for Assigned Names and Number (Icann)

Following the article, there is an opposite situation:

generic top level domain.

Here, on the contrary the first letter is not capitalized while the rest are:

generic top level domain (gTLD).

Could you please explain if there are some rules on how to capitalize the abbreviations or it’s up to the author’s want?

Answer

This is, at least in part, a question of style. Or the style guides of, say, news organizations.

• When you pronounce it as single letters, such as CNN (see en en) or BBC (bee bee see) it is usually written all caps.


• When you pronounce it as one word some organizations write only capital letters, some spell it like a proper noun, first letter capitalized, rest lower case: CNN writes NATO, BBC writes Nato, as you say nato, not en ay tee oh.


• There are lots of exceptions. SCSI is pronounced like a word, SKUZ-ee, but spelled upper case by the BBC, too.