grammar question: how does one properly abbreviate "am" and "pm"

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is it:

1) am and pm;
2) AM and PM;
3) a.m. and p.m.;
4) A.M. and P.M.; or
5) just use military time, you silly american!

i can't seem to find a definitive answer via google.

as a bonus question, is noon am or pm? how about midnight?
(i actually know the answer for this one, but i'm lost on the am/pm thing.)

[Blue_In_AK]

1. In my business

we always do it a.m. and p.m. (I'm a legal transcriptionist), but I don't know why. It's just the way it is in the manual.

[Benhurst]

6. That seems to be the side Random House Webster's Unabridged

Dictionary comes down on, adding that the letters are often capitalized, especially in printed matter.

[WinkyDink]

12. Agreed. It's like i.e. and e.g., for capitalization. It's two words

abbreviated, for punctuation.

[skylarmae]

2. am and pm - noon=pm - midnight=am

[meegbear]

3. I seen it mainly AM and PM ...

and noon is 12:00PM and midnight is 12:00AM.

[RebelOne]

4. I am a copy editor for 10 outdoors magazines

and our standard abbreviation is a.m. and p.m.

[Generic Other]

7. English teacher's choice as well

per every grammar book I have ever used.

[TomInTib]

5. am, a.m., AM,pm,p.m.,PM, all are acceptable.

just maintain some consistency.

noon, PM
midnight, AM

[grasswire]

8. associated press rule is...

...a.m p.m.

In 2003, the Chicago Manual of Style (the standard for magazine grammar) changed its rule from AM PM in small caps to the same style used by AP.

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9. ANSWER to the noon/midnight question:

the correct answer is NEITHER!

am means ante meridiem (before midday) and pm means post meridiem (after midday).

noon being exactly midday is neither before nor after; midnight is equally before one and after the other. in either case, neither am nor pm is technically correct.

to avoid ambiguity, the proper time for the exact midday is "12 noon" and "12 midnight" for the exact crossover from one day to the next.


having said that, the rest of the minute between 12 noon and 12:01 pm clearly falls on the "pm" side of things, so it is convenient to toss 12 noon in with the rest of that minute, resulting in the widespread (but technically incorrect) convention of referring to 12 noon as "pm" and 12 midnight as "am".

[OPERATIONMINDCRIME]

10. Well, Technically, In The Nano Second It Took For A Brain To Register The

exact moment of noon, it would then be 12:00:00:01 right? So since the exact moment precision of noon is less than the calculated time it would take for any living creature to perceive that precise moment, than I guess p.m. would be ok and correct then.

As far as midnight goes, you're wrong altogether there. Even the exact moment of midnight, even if unable to be perceived precisely, would still technically have occured ante meridiem. So a.m. is always ok for midnight.

Peace.

OMC

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13. if you want to figure perception time into it,

then at 11:59.999999999, a half sliver of a second before noon, wouldn't be perceived until 12:00.000000001, a half sliver of a second after noon. so would it make sense to call 11:59.999999999 pm?

and similarly, the exact moment of midnight is also after the previous noon, making pm just as appropriate (or inappropriate) as am.

[WinkyDink]

14. Per this issue: Noon is noon, and midnight is midnight. There is NO

a.m. or p.m. about it. That is, how can noon, the meridien, be POST-meridien, e.g.?

BUT if one MUST: then noon is p.m. as it presages the afternoon, and midnight is a.m.

[muriel_volestrangler]

15. There's no doubt about it; 12:00pm is noon; 12:00 am midnight

True, no-one writes "noon pm" or "midnight am", but 12:00pm (or 12:00:00pm) means the time period, however short, that starts at noon.

[Cleita]

11. I was taught that your #4 was the correct way. However, that

was fifty years ago and many grammar rules and spelling has changed since then.

[Igel]

16. It's not grammar.

It's style.

Different organizations and groups define their styles differently. What's important isn't which you use--although an accepted style is decidedly preferable to an ad hoc one--but that you use it consistently.

Periods or no periods, all-caps, small-caps or lower-case ... pick one and stick with it.

BTW, an older way of dealing with noon, since it's meridian, was 12 m. Chicago Manual of Style 14th edition still sticks with m. for noon, and uses small capitals with a period after each letter and no space for time abbreviations (a.m., p.m., m.). It's what I use, FWIW.

Quibbles over style also include things like commas inside double quotes when it's not actually a quote ("scare quotes", and other things), after the second-to-last item in a list before "and" ("bread, potatoes, and quinoa"). Such quibbles are meaningless as long as clarity is preserved. This is definitely a case where function is more important than form.