When did we go from 12 midnight and 12 noon to 12 am and 12 pm?

In My Humble Opinion
1

This may be more of a GQ, but what the hey. The mods can always move it.

It used to be commonly accepted that the instant of midnight was neither in one day nor the next, and similarly noon was neither morning nor afternoon, but they were both the durationless instant that marked the boundary between days (midnight) or morning and afternoon (noon).

But in the past couple of years, I’ve increasingly seen midnight referred to as 12 am, and noon as 12 pm. Where did this come from? Whose idea was this, and why does it seem to be ubiquitous all of a sudden?

It’s a minor thing, I know, but I find it irritating because I have to stop and think about it each time I see a reference to 12am or 12pm: does that mean noon or midnight?

I can understand the logic of making midnight the ‘am’ and noon the ‘pm’ if you’re going to change it at all (think of a 24-hour clock going from 0000.00 to 2359.59, which would place midnight at the beginning of the day and therefore part of morning), but instinctively (to me, at least) it’s backwards because most of us go to sleep a lot closer to midnight than we wake up, so if I were going to attach those tags to midnight and noon, I’d give ‘pm’ to midnight.

So each time, I have to stop and think: which is it? It only takes a couple seconds to get it straight, but when people said ‘12 noon’ and ‘12 midnight’ it didn’t cause any mental interruption at all.

The thing is, why do it at all? It doesn’t seem to serve any necessity. It’s not like noon and midnight couldn’t be abbreviated to 12 n and 12 m if the need was simply for a shorthand.

One obvious comparison is to the metric system - if we Americans converted to metric like we should have done ages ago, for awhile we’d have to stop and think when we were dealing with liters and kilograms and centimeters and whatnot. But there’d be a point to it: we’d finally have a coherent system of measures, and be on the same page as the rest of the world to boot.

But if there’s a point to the change to 12 am and 12 pm, I’m sure not seeing it.

2

It is probably to allow automated systems to calculate times consistently.

3

My guess is digital clocks. It makes sense to group 12:00 with all the other 12:xx times when it’s just a number and not an actual point on a clock.

4

Digital clocks have been common since, what, the early 1980s? And automated systems that needed to keep time accurately have been around even longer.

But, just as one for-instance, my water bill says the check has to be received by 12 pm on such-and-such a date to avoid the late fee. (I think they meant am, since nobody makes noon the line of demarcation for such things, but this just goes to show that even the county is screwed up by this usage.)

It’s the use of 12 pm and 12 am instead of noon and midnight in human-to-human communication I’m talking about here.

5

I’d go with the explanations in 1 & 2. In that way, it’s useful. Once it becomes a convention, it will not longer be confusing.

Reminds me of the time I gave up on trying to clarify a nightworker’s indication that she went to work “at midnight on Tuesday” and just presumed that she meant right after 11:59PM on Tuesday rather than right after 11:59PM on Monday.

That kind of thing grates me too. I remember that RTFirefly is a statistician. I’m a lawyer. I wonder if that kind of expression tends to particularly irritate people who work with conceptual nuances.
ETA: For meatbag-to-meatbag communication, I’d chalk it up to 1) picking up the habit from automated system or 2) thinking that because the meaning is obvious in the speaker’s head, it must be obvious and no particular attention need be paid to the language through which it’s supposed to go from the speaker’s head to the listener’s head.

6

I didn’t know it ever changed. I’m 57 and midnight has always been 12 AM and noon 12 PM as long as I can remember. I’ve never had to stop and think about it.

7

For me, I think the real irritation is the interruption in reading flow. I read pretty fast (which is probably not unusual in this crowd), and when I slip into reading mode, I’m not even thinking about the fact that I’m reading; I’m just inhaling meanings off the page/screen/whatever. Coming across something that’s not clear takes me out of that state; it’s kinda jarring when that happens. Usually when it happens, it’s because something in the text is unclear, but aside from this, it’s a different thing every time, and is fairly infrequent.

In the case of 12 am and 12 pm, it’s as if someone put speed bumps on a road that you used to be able to drive along almost unconsciously. But now all of a sudden there’s Bump! and another Bump! where there didn’t used to be.

I’m sure I’ll get used to it eventually, and the speed bumps will effectively disappear, but in the meantime, it’s damned irritating.

8

Me too. The person that filled out my birth certificate had a problem with it though (1960). It says I was born at 12:06 p.m. but I was born at 12:06 a.m.

9

I’ve been on this planet 45 years and I’ve never known a time when people have not used those phrases in verbal and written communication. Perhaps it’s a regional thing, and now it’s finally reached your region.

10

I’m with RTFirefly on this; I’ve always (until recently) heard it as noon and midnight in conversation. I blame it on precision from computers spreading into the general populace. Similar to saying a phone number with “oh” instead of “zero”. That’s said mostly with a “zero” these days.

11

I’m 51 and have the same experience. I don’t believe this is a terribly new phenomenon.

12

It annoys me because 12 Noon is neither ante meridiem nor post meridiem; it is the meridiem and occurs exactly when it intends to be, which is noon, Mr. Frodo.

13

I prefer noon and midnight and understand possible confusion over the “You mean midnight between Monday and Tuesday or between Sunday and Monday” issue. It’s easily avoided by telling people to be there at 11:45 pm, or 2345 if you prefer.

14

AM / PM uses fewer characters than Midnight / Noon do.

15

I’ve never heard of any critical use that doesn’t need to distinquish noon and midnight. There’s no way to get people to use AM and PM consistently.

16

When I first learned it, I thought 12 noon was 12 m (meridiem) and 12 midnight was both a.m. and p.m. (both ante & post the meridiem). I don’t know where I got that notion, because it’s clearly not right.

I never use 12 am or 12 pm in writing or speech. If I have to communicate with a stranger, I use “noon” or “11.59 pm,” because “midnight Tuesday” also confuses me.

17

Personally, I prefer the 12 pm / 12 am convention more than midnight/noon if I’m trying to nail down a time to tell someone else; it’s more precise and avoids confusion. But if I’m just say… talking to my wife about when the baby woke up, I’ll say “five after midnight”, since there’s no confusion.

Is it just me, or is this a huge pedantic bitch-fest that’s revolving around whether midnight/noon are specific times, or just some sort of temporal threshold that’s not actually a specific time? Does that really matter in any practical way?

18

:dubious:

12:00 PM = 8 characters.
Noon = 4 characters.

12:00 AM = 8 characters.
Midnight = 8 characters.

19

If “antemeridiem” and “postmeridiem” get abbreviated to AM and PM, “midnight” and “noon” ought to get M and N.

11:59 AM
12:00 N
12:01 PM

Even more character savings!

20

I always thought saying 12 noon and 12 midnight was something people did to avoid confusion about 12 AM and 12 PM. I literally was taught the latter in preschool.