I have studied in school that preposition 'in' has the meaning of 'later' as in:

I will do it in three hours.

But I have been taught at school like preposition 'in' has the meaning of 'inner side of something'.
Why does the 'in' have the meaning of 'later' in the text? Is there any grammar I don't know?
I'd like to know the hidden grammar in this preposition. Please, tell me.

  • 3
    Your example sentence has multiple meanings. If your friend says that the marathon will begin "in three hours", then it will not begin before that time. However, if you say that you will complete it "in three hours", then it will be completed within that time. English prepositions often have several meanings. Jan 28, 2022 at 1:25

1 Answer 1


There is some ambiguity here, as this phrase can idiomatically mean two things:

  • I will complete it within 3 hours
  • I will begin it 3 hours from now.

In the case of the latter meaning, it is really an abbreviation for "in 3 hours time". Saying this in full removes any ambiguity, otherwise we rely on context.

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