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From what I understand, the word "midnight" is usually interpreted incorrectly.

Midnight is written as "12am" which would imply that it's in the morning. Therefore, it should be at the start of the day. On the other hand, both Dictionary.com and the Oxford Dictionary define it as "twelve o'clock at night".

Some examples:

  1. "Midnight on the 10th of December"
  2. "Midnight Thursday"
  3. "Midnight tonight"

are usually interpreted as:

  1. Straddling the 10th and the 11th of December
  2. Straddling Thursday and Friday
  3. Straddling today and tomorrow

but should they technically mean:

  1. straddling the 9th and the 10th of December?
  2. straddling Wednesday and Thursday?
  3. This is much less clear. Technically is there a midnight "tonight", or is midnight "tomorrow morning"?

What do you think? How should "midnight" be interpreted?

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  • 6
    That's why deadlines are usually 11:59 pm
    – Unrelated
    Jul 22, 2016 at 21:18

8 Answers 8

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It's a matter of convention, and the informal convention is that "midnight on the 10th" is more commonly the night between the 10th and the 11th. But the term is awfully ambiguous, and people do use it both ways.

(When I've scheduled things with "midnight" deadlines, I always say "11:59pm on the 10th" or something like that, to avoid the ambiguity. From experience, if you don't people will ask which you mean.)

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  • 8
    As a programmer, I deliberately avoid the ambiguity as well. "By the end of the 10th", or "Before the 11th" generally work as well.
    – Damovisa
    Dec 9, 2010 at 5:42
  • Thank you so much @Damovisa. I'm actually sitting right now trying to fix ambiguous period description in the app that I'm working on and "By the end of the 10th" is a perfect way to be unambiguous.
    – Rafał Cieślak
    Mar 9, 2019 at 15:05
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By most definitions, the date changes at midnight. That is, at the precise stroke of 12:00:00. That time, along with 12:00:00 noon, are technically neither AM or PM because AM and PM mean "ante-meridiem" and "post-meridiem", and noon and midnight are neither ante- nor post- meridiem. However, for convenience, most people lump the 12:00:00 time with its nearest neighbour, 12:00:01, which IS AM or PM.

Since the date changes at the stroke of midnight, there is always ambiguity about which date you refer to. Midnight on the 10th technically means at the start of the 10th, but when most people speak they mean it to be at the end of the 10th.

If I said "I'll meet you Friday at midnight" or "I'll meet you Friday night at midnight" you (and most people) would probably interpret both times as the midnight that follows Friday noon. However, there are cases where the first sentence really means "the midnight at the start of Friday".

Since the common usage conflicts with the technical definition, if you want to be totally clear, use other words or other times.

Friday night at midnight

probably will always be interpreted as "Midnight in the night which follows Friday evening".

Midnight tonight

This means (to me) the midnight following today.

11:59 PM Friday

12:01 AM Saturday

These are totally unambiguous.

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  • I think this summarises what I'm getting out of these answers. Technically, "midnight" doesn't belong to either day, but conventionally it's usually understood at the end of a day not the beginning.
    – Damovisa
    Dec 9, 2010 at 22:32
  • Note that leap seconds, when they occur, typically are inserted at 23:59:60 UTC. Eg, there was one a month ago, at 30 June 2012, 23:59:60 UTC. At that midnight, 23:59:59 and 00:00:00 were 2 seconds apart instead of 1.
    – James Waldby - jwpat7
    Jul 27, 2012 at 19:10
  • @jwpat7 Note that leap seconds occur simultaneous thought out the world. With local time, that extra second may be in the morning or afternoon, not near local midnight - unless your timezone matches UTC.
    – chux - Reinstate Monica
    Jun 9, 2015 at 20:32
  • @chux, yes, of course; that's the usual nature of UTC times.
    – James Waldby - jwpat7
    Jun 11, 2015 at 3:59
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Another way to avoid ambiguity is to use a 24 hour clock. Midnight between Thursday and Friday is 2400 Thursday, and 0000 Friday.

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  • 2
    This is support by @ISO 8601
    – chux - Reinstate Monica
    Jun 9, 2015 at 20:35
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    @chux-ReinstateMonica - Apparently no longer. 'Midnight is a special case and may be referred to as either "00:00" or "24:00", except in ISO 8601-1:2019 where "24:00" is no longer permitted.'
    – MrWonderful
    Apr 24, 2020 at 22:30
  • 1
    @MrWonderful LSNED
    – chux - Reinstate Monica
    Apr 25, 2020 at 0:04
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The convention stems from the term itself. Midnight comes from 'mid-night.'

In conversation, the 'night' of which 'midnight' is in the middle, is considered the night of the date mentioned.

If you are referring to a deadline, this also will refer to the stroke of 12 after the evening of the same date.

Example:

The paper is due by Friday at midnight.

Should not be confusing to anyone. Plus, since the only confusion could possibly be that it was due a day earlier, there can be no misunderstanding excuse for not getting the paper in on time. ;-)

The entire convention is based on the typical human schedule of being awake during the day and asleep during the night. Even the 'wee hours' can be used conversationally to mean the 'night' prior.

Example:

We stayed out Friday night until 3am!
We were out until 3am Saturday morning!

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  • 3
    This is a good answer, but experience shows that you're wrong -- it can be confusing, and to many people. Stamping your feet about how illogical and unthinking humans are doesn't change that fact...
    – Jonah
    Sep 24, 2016 at 17:50
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If we apply your argument to 12pm, being labeled in that fashion implies that it is in the evening, and therefore it must be at the end of the day. Thus, people are wrong to go around calling it "noon", which is clearly in the middle of the day, not the end. :-)

By convention, "midnight on the 10th of December" should refer to the end of the day of December 10, the instant before December 11 starts. If I say "last midnight" you can be assured that I am referring to a time less than 24 hours ago, and if I say "midnight tonight" I am referring to a time less than 24 hours in the future.

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  • Ooh, very good point RE noon :) I think the learning here is that it's convention that really defines the meaning.
    – Damovisa
    Dec 9, 2010 at 5:31
  • If you want to be pedantic, 12:00:00pm is not a valid time. The PM part means "post meridian" which 12:00:00 is not. It is merely convention that 12:00:00 (which follows 11:59:59am and is followed by 12:00:01pm) is labelled 12:00:00pm. The point remains that midnight touches two dates and is technically part of the start of the day not the end. Your examples of "last midnight" and "midnight tonight" provide enough additional context to remove any ambiguity about which midnight the speaker means.
    – Mr. Shiny and New 安宇
    Dec 9, 2010 at 15:22
  • Whoops, RegDwight corrected me on my answer, but I didn't notice I made the same mistake here. PM means Post Meridiem not Meridian.
    – Mr. Shiny and New 安宇
    Dec 10, 2010 at 14:23
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The existing answers are already good, but for anyone who might get confused, I think this might be an easy way to remember the common definition: "Friday midnight" means "middle of Friday night".

Since Friday night pretty much never refers to early morning Friday, it stands to reason that neither does the middle of Friday night.

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If you look at most writing and scientific guides, there is no such thing as 12 a.m. or 12 p.m. Technically, you should refer to 12 noon or 12 midnight. It's technically neither. It's just midnight. The abbreviations for am and pm come from the Latin words "ante meridies" (am) and "post meridies" (pm). Meridies means noon, so post meridies means after noon and ante meridies means before noon. Since the date changes at the stroke of midnight, there is always ambiguity about which date you refer to. Midnight on the 10th technically means at the start of the 10th, but when most people speak they mean it to be at the end of the 10th. In 24-hour time notation, "00:00" and "00:00:00" refer to midnight at the start of a given date.

See also: Is Midnight Am PM?

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TL;DR: "Midnight" should only be used where the night is certain or conceptional. Conceptionally the individual night does not matter. In denoting a specific point in time, clarify the night (not just the day) - especially when on a deadline.

Colloquial use can be a strong argument if a term stands firm in the language. If you are reading this then the term does not stand firm. Ultimately, you will have to observe or ask others how they use "midnight [of xday]" - which is how colloquiality arises. Colloquere, colloquere!

Repeating some thoughts others uttered in order to elaborate

"AM" stands for "ante meridiem" and "PM" for "post meridiem", meaning before and after midday respectively. "Midday" relates to a certain or conceptional day, not a night. In the same way, "midnight" relates to a certain or conceptional night, not a day.

While definition-wise midnight should be neither AM nor PM, from philosophical and technical points midnight is both preceeding and succeeding (some) midday thus being both AM and PM; dito midday.

Binding midnight (and midday) to AM or PM and still avoiding ambiguity requires understood convention which works in small, agreeing and identified groups only and so makes for bad use in wider language where the group and convention of a speaker is not easily identified.

It may be more useful to have 12 CM (contra meridiem, opposite midday) for midnight and 12 HM (hoc meridiem, this midday) for midday - relating to conceptional terms rather than any specific midday or day.

Reacting

Damovisa:

Midnight is written as "12am" which would imply that it's in the morning. Therefore, it should be at the start of the day.

Hellion:

If we apply your argument to 12pm, being labeled in that fashion implies that it is in the evening, and therefore it must be at the end of the day. Thus, people are wrong to go around calling it "noon", which is clearly in the middle of the day, not the end.

So while "12am" may claim to be before midday it may just be treated as a synonym to "12pm" (marrying the arguments of Damovisa and Hellion) - with both designations being utterly useless to disambiguate except for standing convention. So the "12" may be more significant. I do not know of any clock (as opposed to what is called a "timer" - ugh), calendar or other time-giver counting time down. Assuming a count-up, "12" has come after some "11" and something has been counting up a dozen times. That rather relates "12am" to whatever happened before. This could argue for midnight belonging to the day before.

Mr. Shiny and New 安宇:

However, for convenience, most people lump the 12:00:00 time with its nearest neighbour, 12:00:01, which IS AM or PM.

There could be an argument for convenience here if "nearest" was effectually defined. Time-wise, 11:59:59 (or 23:59:60) is no further away and offers no less convenience.

MrWonderful:

In conversation, the 'night' of which 'midnight' is in the middle, is considered the night of the date mentioned.

This replaced the ambiguity of "X's midnight" with that of "night of the date". This can only help if the night is sufficiently specified by the date which may not be the case.

Conclusion

(Y)Our mission, syctai, is to clarify the night before using "midnight" - unless speaking conceptionally.

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  • You seem to be using an answer to comment on other answers. Please don't do that: write an answer of your own.
    – Andrew Leach ♦
    Mar 16, 2020 at 9:21
  • I think I wrote an answer of my own, pretty much summed up in the first or last sentence. Could you elaborate on how this is not an answer to OP, please? I also commented on parts of other answers in order to deal with what can be considered arguments counter to mine.
    – valid
    Mar 16, 2020 at 13:09

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