# Why do some abbreviations not use periods?

**URL:** <https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721>\
**Category:** Factual Questions\
**Created:** [April 23, 2004, 11:01pm UTC](https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721 "2004-04-23T23:01:10Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![1000monkeys](https://avatars.discourse-cdn.com/v4/letter/1/7cd45c/32.png) [@1000monkeys](https://boards.straightdope.com/u/1000monkeys)\
**Post date:** [April 23, 2004, 11:01pm UTC](https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721/1 "2004-04-23T23:01:10Z")

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I was going to ask “not require” periods, but I think (at least according to MS Word’s spellchecker) that its not even optional in cases like:

CEO

and

COO

and, I think, the PO

in Post Office Box.

Why the heck not?  
and what are some others?

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**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\
**Post date:** [April 24, 2004, 1:31am UTC](https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721/2 "2004-04-24T01:31:24Z")

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Generally, according to most modern style guides, abbreviations only use periods when they might be confused with an actual word (in. for inch, for instance). Most others do not. According to **The Chicago Manual of Style** :

> [@](#):
>
> 14.2 . . . The trend is now strongly away from the use of periods with all kinds of abbreviation that have carried them in the past. In our view, this is to the good.

This is from the 13th Edition, but I think the newer one would agree.

Of course, it’s all on a case-by-case basis, ultimately.

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**Author:** ![ReuvenB](https://avatars.discourse-cdn.com/v4/letter/r/9fc348/32.png) [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)\
**Post date:** [April 24, 2004, 2:01am UTC](https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721/3 "2004-04-24T02:01:07Z")

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[The master speaks.](http://www.straightdope.com/classics/a2_244a.html)

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**Author:** ![ReuvenB](https://avatars.discourse-cdn.com/v4/letter/r/9fc348/32.png) [@ReuvenB](https://boards.straightdope.com/u/ReuvenB)\
**Post date:** [April 24, 2004, 2:02am UTC](https://boards.straightdope.com/t/why-do-some-abbreviations-not-use-periods/241721/4 "2004-04-24T02:02:53Z")

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Heh. I should probably read the entire OP before I respond to things.  
Usually, you don’t use periods with acronyms, such as what you’ve described.