Contact me at 5 o'clock on a Monday in the new year

There are many resources which explain the rules about which preposition to use for time phrases to English learners, e.g.

  • We use at with: with particular points on the clock; with particular points in the day; with particular points in the week; with special celebrations.
  • We use on: with dates; with a singular day of the week to refer to one occasion; with a plural day of the week to refer to repeated events; ...
  • ...

From the online Cambridge Dictionary

It seems to be a list of special cases. It doesn't look like there is one linguistic property that can be pointed to to classify at-times from on-times from in-times.

I am interested in how we came to use each of these prepositions for the time expressions that they are currently used for. Why do we not, for example, say "meet me at Monday"? This is interesting because looking only at present-day English, the rules about which preposition to use for which "type of time" seem arbitrary.

  • Are you asking why do these words mean what they mean?
    – user405662
    Commented Mar 6 at 7:28
  • @user405662 I'm asking, how did English arrive at using them this way? It's interesting because looking only at present-day English, the rules about which one to use for these kinds of time-phrases seem arbitrary.
    – minseong
    Commented Mar 6 at 7:53
  • It's useful to have different prepositions for different functions, because on hearing a preposition you immediately know what kind of information will follow. Languages aren't devised to be easy to learn, but grow naturally to be useful for speakers. What preposition comes to be used for what function is often arbitrary, although you can probably trace influences from Latin, Norman French, and other languages (but then you'd have to explain why Latin uses certain prepositions and cases, which is also arbitrary).
    – Stuart F
    Commented Mar 6 at 9:47
  • 1
    If you really wanted, you could get access to the OED and read the entries for the various prepositions to see how their use has changed historically. But in the main, it catalogues a lot of competing influences, some of which happened to win out arbitrarily.
    – Stuart F
    Commented Mar 6 at 9:48

1 Answer 1


at refers to the time as timepoint during the day or during the month or during the season or during a calendar year.

Let's meet at 3PM.

We were there at Easter.

They perform this ceremony at the new moon.

They make a special offering to their deities at planting time.

on refers to the time as occasion.

The parade is on New Year's Day.

The parade is on Easter Day.

The convention will be held on June 15th.

in refers to the time as timespan.

I expect to see them in the next week or two.

In this new electric kettle water comes to a boil in only a few minutes.

  • Why does Monday not count as a timepoint during the week and thus use at ?
    – minseong
    Commented Mar 6 at 13:08
  • Because Monday refers to a 24-hour span so at doesn't work, and if it serves as the occasion for something, we'd use on. "The crime happened in the early morning hours on Monday."
    – TimR
    Commented Mar 6 at 13:52
  • How is planting time a timepoint? Isn't Easter a day, even when we don't use the word day to refer to it?
    – jsw29
    Commented Mar 6 at 18:04
  • These are aspectual meanings and the same thing can be seen from more than one angle. Planting time can be a timepoint or moment in two different ways, when a plant or seed is actually placed in the ground, the literal moment of planting, and also when the omens or natural signs say that now is the moment for planting. A similar thing happens with solstice. It is both a day with duration and a tick on the calendar timeline. Easter is a feast on a liturgical calendar and Easter Day is the occasion of the feast.
    – TimR
    Commented Mar 6 at 19:13
  • @TimR "The crime happened on January". "New moon" and "planting time" are also timespans
    – minseong
    Commented Mar 7 at 10:16

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