You can't learn English overnight.

You can't learn English in one night.

I know that "in one night" may not sound idiomatic, so I should say "overnight" to sound natural.

I often hear "overnight" to mean "a short period of time".

However, when I think about it as a structure, I can't find a good reason why it is "overnight" instead of "in one night". The other periods of times "in one day/week/month" is very common in English. And we cant use "over" with them, for instance "over a day, over a week" to mean something can not be achieved in short period of time.

So, is there something special with the word "night", that prevents us from saying "in one night"? Or is it simply a matter of being idiomatic?

  • 3
    Who told you that in one night was wrong? Jan 16, 2022 at 14:03
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    I always hear native speakers say "overnight" and never hear from them "in one night". Maybe they use it but it may not as common as "overnight". Secondly, if you search google "in one night", it brings less results than it does with "overnight". Thirdly, why do they not say "overday" but "overnight" to refer to a short period of time.
    – Yunus
    Jan 16, 2022 at 14:09
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    Overnight is commonly used in the sense of 'between one day and the next' when referring to a sudden change ('hair turned white overnight'), or when referring to an overnight stay somewhere. I would understand 'learning English in one night' to refer to a single evening's study. Jan 16, 2022 at 14:22

1 Answer 1


You can't learn English in one night.

Is a correct and idiomatic English sentence. It means that you can't learn English by studying for a single period of darkness. It might be used to tell students that they need to study for a long period of time, and not just cram on the night before a test.

... overnight.

is normally a metaphorical comment about something happening very suddenly and unobserved (but perhaps not literally "during the night")

The rest of your question is just idiom. There is an idiomatic expression "overnight" and not "overday"... sorry but there is no logic here.

It certainly is possible to use "over a day".

You do not need to achieve [a balanced diet] with every meal, but try to get the balance right over a day or even over a week. (Eat well guide from UK government)

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