I know that the preposition 'on' and 'in' are used in the following contexts

1. He came in the morning.

2. He came here on Sunday morning.

3. He came here on 2nd october.

4. He came here on october 2nd, 2018.

I know that in the sentence1 the preposition 'in' is used since morning is rather a long period.

In the sentences 2,3 and 4 'on' is used because it is followed by day or date. Even the third sentence refers to date though it is followed by the month December.

I would like to know why we say:

He came here on a fine morning

and not:

He came here in a fine morning.

Here morning does not refer to any day or date and refers to a period of time.

Is it because of the article a or something else?

It is not a duplicate of "in the morning vs on the morning".

1 Answer 1


Generally speaking, the event happened "on" a calendar date or "in" a time period. I don't know if there's a formal grammar rule to that effect but that's how it works. You have correctly described standard usage (at least for US English).

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