What is the capitalization rule for acronyms? E.g., why "radar" and not "RADAR" but "NATO" and not "nato"?


I think this has a lot to do with the fact that certain acronyms were intended as (or have become) the general words for certain things, and others are actual names for things.

"NATO", for instance, is an abbreviation for the formal name of an organization; as such, it seems obvious that you have to leave it in all caps.

"Radar" and other words such as "laser", on the other hand, are invented words for newly invented phenomena. The fact that they come from acronyms is almost beside the point, since they could have been instead named by inventing Latinate or Greekish words (such as *collimolux or *syngrammophos (yuck on both counts)) as sometimes happens in science. They are simply coinages and thus bear only an etymological relationship to the original acronym, and therefore we use them as "normal" words, which includes dropping the all-caps on them.

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    This is incomplete, however. Some organizations write Unesco and others UNESCO (definitely a proper noun), and a bank pin is something different from a bank PIN (definitely not a proper noun). – choster Apr 5 '17 at 17:54
  • I am not sure how to account for Unesco vs. UNESCO (though, personally, I would stick with UNESCO for some reason that is hard to detail). However, pin is already a word, and this may be why you see PIN; on the other hand, I have no personal problem with the phrase pin number (even though the N becomes redundant, which is probably a whole other topic). – Roni Choudhury Apr 5 '17 at 17:56
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    You can argue it is about lexicalization; works from the 1950s often used SCUBA, but that faded by the 1970s. Similarly, almost no one remembers that care packages began as CARE packages. But there isn't universal consensus on what is lexicalized or not. It's a point of style. If your editors want you to write Aids, you use Aids; if they prefer AIDS, you use AIDS, and if they prefer A.I.D.S. you bite your tongue and use A.I.D.S. As you note they would probably not impose aids, as thankfully it never became the primary meaning of that word, in contrast to email. – choster Apr 5 '17 at 18:14

The word anacronym is relevant here.


an acronym that few remember what the letters stand for, such as laser and radar

Generally, once a word becomes so frequently used that its acronymic etymology is less relevant, the capitalization is dropped.

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