My brother was saying that is grammatically correct to say he went to sleep at one today because it was after 12 o' clock, but I say it should be he went to sleep at one o'clock yesterday. Which one of us is correct?

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    People overuse the term "grammatically correct" for telling logical and unlogical sentences apart. Is the sentence "In the mathematics, I saw a smell glow." grammatically correct? Yes. Does it make any sense? No. Commented Jan 22, 2019 at 15:10

5 Answers 5


This is not a matter of grammar but of semantics and idiom. I don't think most native speakers would use either "today" or "yesterday"; we'd say

I went to bed at one o'clock last night or
I went to bed at one o'clock this morning.

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    For context, you'd probably use 'this morning' if you wanted to emphasise the fact that you went to bed late. Commented Jan 22, 2019 at 11:10
  • @Ynneadwraith But should I use «this morning» even if one o'clock is the time I go to bed when I want to sleep early so for me it's not really late? My usual bedtime is around 2:00 ~ 2:30 AM
    – Elie G.
    Commented Jan 23, 2019 at 6:36
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    @DrunkenPoney Generally speaking, no. "Night" encompasses pretty much all the dark time between sunset and sunrise, so "this morning" is mostly just to emphasize that it's an abnormal situation. Commented Jan 23, 2019 at 7:30
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    When discussing late-night times with people and especially when something is "yesterday" or "today", often somebody chimes with some somewhat humorous rules for determining it. The one that stuck with me is "The day changes after you sleep" usually followed shortly with "...or when the sun rises. Whichever comes sooner". But there really isn't one true answer for hours just after midnight. If you say either of the suggested phrases, or even do use "today" or "yesterday", people should understand what you mean.
    – VLAZ
    Commented Jan 23, 2019 at 13:33

Good question! I agree with the comment that choosing "last night" or "this morning" is a matter of emphasis - If you want to stress that it was inconvenient or unusual for you, I'd suggest using "this morning"; if you were out with friends or it's normal for you to go to sleep in the early AM hours, I'd suggest using "last night".

As a matter of personal convention, I use 5am as the cutoff between "last night" and "this morning". At 5am it's unambiguously the morning or a new day, but 2 or 3am could easily still be considered a continuation or part of the same night that technically ended after 11:59pm


rexkogitans's comment to your question is correct. What you're asking is not an issue with the sentence's structure, and is not a question about grammar.

Most people will say that the day starts at midnight (12:00am). Some religious groups have been known to say that a new day starts at sundown, which would make this question moot.

Presuming that you accept that the new day starts at midnight, the technically correct answer is that 1:00 am was from today. However, if the person normally starts sleeping somewhere from 8pm-11:30pm, and simply did an unusual thing by starting sleep later on this particular night, then some people might say "I didn't go to bed last night until 1 am". Even though this wasn't actually "last night", that is when the person started the sleep session that would typically have started last night, so people might decide to use words that act that way.

While such a choice of words would be considered technically inaccurate, I have certainly heard people talk that way. I side with your brother, but many people would understand what you mean, and there's a good chance that it wouldn't cause much confusion.


Let's look at this another way. Today is Wednesday (at least where I am!) and brother went to bed at 01h00 on this day - this morning. If you think that it's yesterday, surely he'd have gone to bed at 01h00 on Tuesday. But it wasn't: it was Wednesday, the same day it still is. So logically, the correct phraseology is 'I went to bed at 01h00 today'.Which is just one hour after today (Wednesday) started. Not 25 hours ago...

Day or night doesn't really come into the equation - you both might be at the North Pole for all we know!

  • Downvoter - if you had a good reason, why not share it?
    – Tim
    Commented Jan 24, 2019 at 14:54

Well if one considers morning after the sunrise - then saying yesterday night at one is correct but if the one is considering morning past 00 hrs then Today might sound correct - but i will disagree in context with it as per my understanding To(day) refers to the period post dawn of new day (post sunrise).

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    Similar, but consider morning is when you get up (in the am). So for people that get up very early (eg 3am - train drivers/binmen etc) they still get up today even if it's before sunrise. By this definition, you always go to bed yesterday because today is when you woke up. (except cases where you go to bed at unusual times such as shortly after lunchtime then get up the same "day").
    – fdomn-m
    Commented Jan 22, 2019 at 8:56
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    As StoneyB points out, the exact time one day becomes the next is not a grammatical issue, but a convention issue. One convention is that the new day starts at midnight. In the Jewish calendar, a new day starts at sunset. If enough people agreed a new day started at noon, that would be a convention too.
    – CJ Dennis
    Commented Jan 22, 2019 at 12:01
  • I dont deny with Freedom-m's comment - there are exact times when it is declared as next day - not after sunrise and stuff - It is a clear notation for managing the 24 hrs cycle completion. Else - separate location wise - separate time cycle would have been impossible - as sunrise time differs from location to location. But dont you thing - the night - term is used in the dark hours or absence of sun. Hence mornings still be considered better post / around sunrise. Commented Jan 22, 2019 at 12:24
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    It doesn't matter what you or I think if it's too far from the consensus. If I decide the new day starts at exactly 12:23 am, well good for me! But I'm unlikely to get many, if any, other people to agree with me. If "day" is only the bright part, a day is on average 12 hours long, starts at sunrise and ends at sunset. However, "day" is both a 24 hour period, and the part of the 24 hour cycle when the sun is above the horizon. The two definitions are incompatible with each other.
    – CJ Dennis
    Commented Jan 22, 2019 at 12:49

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