# Midnight: AM or PM? **URL:** \ **Category:** Factual Questions\ **Created:** [October 29, 2003, 4:02pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247 "2003-10-29T16:02:27Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Melraidin](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@Melraidin](https://boards.straightdope.com/u/Melraidin)\ **Post date:** [October 29, 2003, 4:02pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/1 "2003-10-29T16:02:27Z")
I’ve searched the archives and this is the closest thread I could find to answering my question: [http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=63917&highlight=midnight+noon](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=63917&highlight=midnight+noon) Also found only a single useful link from Google, to a Yahoo message board. While this was helpful, it wasn’t necessarily the most authoritive answer. So could someone please answer the question, is midnight AM or PM? Same with noon. My position is that they are both simply transitional times, with no valid AM or PM designation, along the same lines as zero is neither postivie nor negative. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 29, 2003, 4:05pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/2 "2003-10-29T16:05:07Z")
> [@](#): > > \*Originally posted by Melraidin \* > \*\*My position is that they are both simply transitional times, with no valid AM or PM designation, along the same lines as zero is neither postivie nor negative. \*\* I agree, although they may have AM or PM designations that exist as a matter of convention, rather than logic. ---
**Author:** ![jeffjuiliano](https://avatars.discourse-cdn.com/v4/letter/j/a698b9/32.png) [@jeffjuiliano](https://boards.straightdope.com/u/jeffjuiliano)\ **Post date:** [October 29, 2003, 4:06pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/3 "2003-10-29T16:06:55Z")
midnight is am and noon is pm ---
**Author:** ![Bytegeist](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bytegeist](https://boards.straightdope.com/u/Bytegeist)\ **Post date:** [October 29, 2003, 4:28pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/4 "2003-10-29T16:28:38Z")
[They are neither AM nor PM](http://www.boulder.nist.gov/timefreq/general/misc.htm) — though obviously many people add those qualifiers anyway, so it pays to be prepared. ---
**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\ **Post date:** [October 29, 2003, 4:29pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/5 "2003-10-29T16:29:16Z")
The way I remember it, whether “official” or not, is that 11:59 is in one of the designations, and 12:01 is in the other. The moment when AM becomes PM (and vice versa) is 12:00. So as PM becomes AM (midnight) 12:00 is AM. Same “logic” for noon. The “M” is “meridiem” and refers to “midday” or “noon” so that “AM=ante(before)meridiem(noon)” and “PM=post(after)meridiem(noon)” are what those designations mean. If 11:59 AM is the last minute before noon, and 12:01 PM is the first minute after noon, and 11:00 AM is the last hour before noon, and 1:00 PM is the first hour after noon, then 12:00 has to be associated with all the minutes associated with the 12:xx hour, and since all those minutes (01-59) are all PM (after noon) then the 12:00 minute/second has to be with them as a PM minute/second. All the confusion can be avoided in those systems that allow “noon” and “midnight” as designations. But in those things like digital clocks/timers where it can only be “am” or “pm” you need the “logic” I’ve described here. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [October 29, 2003, 5:32pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/6 "2003-10-29T17:32:54Z")
Zeldar got it right. 00:00:00 (midnight) is AM 12:00:00 (noon) is PM. 23:59:59 is the last second of PM 11:59:59 is the last second of AM ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [October 29, 2003, 5:46pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/7 "2003-10-29T17:46:24Z")
If my digital clock says 12:00pm, then the moment of Noon has very recently occurred. 12:00pm is in the middle of the day, 12:00am is in the middle of the night. Asking whether noon is am or pm is like asking whether the US/Canada border is in the US or Canada. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 29, 2003, 8:22pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/8 "2003-10-29T20:22:51Z")
Midnight and noon are neither AM nor PM. However, when digital clocks became common, no one thought it worth the effort and complexity to add “Midnight” and “Noon” designations. Thus at midnight they would simply say “12:00AM.” Furthermore, while the specific instant of midnight is neither AM nor PM, the instant immediately after it is AM, so for 99.999…% of the minute from midnight to 12:01 it is indeed AM. It makes sense to fashion clocks this way, but the unfortunate side effect is a generation or two of folks who think that midnight and noon are AM and PM, respectively. ---
**Author:** ![PaperTowel](https://avatars.discourse-cdn.com/v4/letter/p/ecb155/32.png) [@PaperTowel](https://boards.straightdope.com/u/PaperTowel)\ **Post date:** [October 29, 2003, 8:32pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/9 "2003-10-29T20:32:48Z")
Yes, very unfortunate. ---
**Author:** ![porcupine](https://avatars.discourse-cdn.com/v4/letter/p/ac91a4/32.png) [@porcupine](https://boards.straightdope.com/u/porcupine)\ **Post date:** [October 29, 2003, 9:46pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/10 "2003-10-29T21:46:12Z")
[url=“[http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-57026](http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-57026)”]NIST says that 12 midnight is neither am nor pm.[/url} However, I believe another standards body defines midnight as 12 am, but I cannot find a link right now. ---
**Author:** ![porcupine](https://avatars.discourse-cdn.com/v4/letter/p/ac91a4/32.png) [@porcupine](https://boards.straightdope.com/u/porcupine)\ **Post date:** [October 29, 2003, 9:47pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/11 "2003-10-29T21:47:48Z")
[Fixed link](http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-57026) ---
**Author:** ![brianmelendez](https://avatars.discourse-cdn.com/v4/letter/b/65b543/32.png) [@brianmelendez](https://boards.straightdope.com/u/brianmelendez)\ **Post date:** [October 29, 2003, 9:58pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/12 "2003-10-29T21:58:57Z")
From _The Chicago Manual of Style_ (15th ed. 2003), 9.43 at 391: > [@](#): > > _Noon and midnight._ Except in the twenty-four hour system (see 9.44), numerals should never be used to express noon or midnight. Although noon can be expressed as 12:00 m. (m = _meridies_), very few use that form. And the term 12:00 p.m. (midnight) may well be misinterpreted. In the second example below, note the double date for clarity. > > The meeting began at 9:45 a.m. and was adjourned by noon. > Rodriguez was born at midnight, August 21-22. From Kate L. Turabian, _A Manual for Writers of Term Papers, Theses, and Dissertations_ (Chicago: 6th ed. 1993), 2.57 at p. 33: > [@](#): > > Midnight is written as 12:00 P.M., noon as 12:00 M. (“meridian”). From the United States Government Printing Office, _Style Manual_ (2000), 12.9.b at 182: > [@](#): > > 12 a.m. (noon); 12:15 p.m. (15 minutes past noon) > 12 p.m. (midnight); 12:25 a.m. (25 minutes past midnight) Thank you, **Bytegeist** and **porcupine** , for taking the trouble of giving a citation instead of just an opinion. ---
**Author:** ![brad\_d](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@brad\_d](https://boards.straightdope.com/u/brad_d)\ **Post date:** [October 29, 2003, 10:46pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/13 "2003-10-29T22:46:21Z")
Whether it’s officially sanctioned by anyone or anything, a study of the behavior of most digital clocks/watches will show that “the industry” seems to have adopted the convention that noon is 12:00 p.m., and midnight is 12:00 a.m. Microsoft Outlook, hardly a valid reference for correctness but something whose errors must be lived with, does the same thing. The cites given by **brianmelendez** state just the opposite. :smack: To make matters worse, the (stylistically correct) “12:00 M.” designation would probably stand an excellent chance of being interpreted as “12:00 midnight,” as it is quite true that this form is very rarely used. (I’ve never seen it, myself.) While I certainly put stock in the _Chicago_ and Turabian cites, they’re so directly at odds with common usage that I don’t think I’d dare express a time that way if I actually wanted to be understood. So…we have conflicting citations. _Chicago_, Turabian, and Government Printing Office agree (more or less) on one answer. The NIST dissents. :dubious: This is a much more difficult question than I’d have thought… ---
**Author:** ![vd](https://avatars.discourse-cdn.com/v4/letter/v/b19c9b/32.png) [@vd](https://boards.straightdope.com/u/vd)\ **Post date:** [October 29, 2003, 10:54pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/14 "2003-10-29T22:54:33Z")
I guess you could consider digital clocks to be correct. By the time the LED’s (or LC’s or whatever) have taken their microseconds to transition to 12:00 at noon, it is now P.M. (in the clock’s own time reference of course). ---
**Author:** ![jmonster](https://avatars.discourse-cdn.com/v4/letter/j/dbc845/32.png) [@jmonster](https://boards.straightdope.com/u/jmonster)\ **Post date:** [October 29, 2003, 11:16pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/15 "2003-10-29T23:16:50Z")
How can noon be (literally) “after noon”? The two twelves are technically neither am nor pm, but since everyone pretty much says noon is pm and midnight is am, it’s good enough to get by. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 29, 2003, 11:28pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/16 "2003-10-29T23:28:44Z")
Whether noon is AM or PM depends on your convention, but by any convention, if a clock is showing the time 12:00 during the day, it’s PM. Similarly, at night when the clock shows 12:00, it’s indisputably AM. This does not say anything about whether the exact moment of noon or midnight is AM or PM, but it’s a logical guideline for what convention to use. ---
**Author:** ![GawnFishin](https://avatars.discourse-cdn.com/v4/letter/g/e9bcb4/32.png) [@GawnFishin](https://boards.straightdope.com/u/GawnFishin)\ **Post date:** [October 30, 2003, 7:42am UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/17 "2003-10-30T07:42:28Z")
My two cents worth, **Zeldar** got it right. Wasn’t mans first method of measuring time a sundial? And since the sun we see in the sky is 8 minutes 18 seconds old and there fore post meridiem and hence PM. One could argue the same for midnight being past the meridiem however, since all of the sun dials with the noon meridiem clearly marked didn’t work well at all for displaying midnight. They kinda figured that 12:00 midnight is the first moment of an equally divided clock and since noon was past the noon meridiem midnight must be before the meridiem. So convention or not it kinda makes sense doesn’t it. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [October 30, 2003, 3:15pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/18 "2003-10-30T15:15:53Z")
Oh, so I guess that 11:52 in the morning is PM. Thanks for clearing that up. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 30, 2003, 4:55pm UTC](https://boards.straightdope.com/t/midnight-am-or-pm/210247/19 "2003-10-30T16:55:50Z")
One thing of which you can be certain – if you call either noon or midnight either AM or PM, some folks will construe it as the opposite of what you intended. If you want to be clearly understood by all, use the terms “noon” and “midnight.”