# Midnight: AM or PM?

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.

I agree, although they may have AM or PM designations that exist as a matter of convention, rather than logic.

midnight is am and noon is pm

They are neither AM nor PM — though obviously many people add those qualifiers anyway, so it pays to be prepared.

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.

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

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.

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.

Yes, very unfortunate.

[url=“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.

From The Chicago Manual of Style (15th ed. 2003), 9.43 at 391:

From Kate L. Turabian, A Manual for Writers of Term Papers, Theses, and Dissertations (Chicago: 6th ed. 1993), 2.57 at p. 33:

From the United States Government Printing Office, Style Manual (2000), 12.9.b at 182:

Thank you, Bytegeist and porcupine, for taking the trouble of giving a citation instead of just an opinion.

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…

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).

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.

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.

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.

Oh, so I guess that 11:52 in the morning is PM. Thanks for clearing that up.

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.”