“On Sunday evening” or “In the Sunday evening”

Question

Everyone knows we use “in” for these terms

In the evening, In the morning, in the afternoon. And for days, we use the preposition “on”, on Saturday, on Monday, on Tuesday,...so on.

With respect to both of them being “nouns”, Sunday and evening.

But I am confused of using them together.

• I met one of my friends on Sunday evening.

Why do we use ON instead of:

• I met one of my friends in the evening of Sunday.

• I met one of my friends in Sunday evening

Here, in the last sentence, I used IN Sunday evening, as we do with “On school vocation”; ON related to vocation, not school. So here IN related to evening, not Sunday.

Answer 1

Use of prepositions in English is not a case of "why", but rather a case of "because" that is the way we do it.

Generally, we use "on" with specific days, or dates. Sunday evening is a specific day. If we were to use "the evening" on its own, it could refer to any evening, and is not therefore a specific day or date.

I really do wish I could tell you "why" we use on, but it would seem to be a rather arbitrary choice, with no particular logic to it.

More info here: In, at, on + Time or Date

It might be pertinent to note that other language use different ways of expressing the same ideas. In French for example, prepositions are not used at all with days of the week.

Answer 2

Sunday is understood to be a particular place in the week or in calendar time, hence on.

On June 24th.

On Sunday.

Sunday evening and Sunday can both be fluid in their meaning, referring to either a duration of time:

We waited for your call all Sunday evening.

We waited for your call all evening, Sunday.

We waited for your call all day, Sunday.

We waited for your call all Sunday.

and to a place in time:

We met on Sunday.

We met on Sunday evening.

When understood as a nameworthy chunk of time during the week vis-à-vis the week, they are thus a place in time, an identifiable spot along the way^†, as it were, hence on Sunday evening.

You can drop the preposition:

I met one of my friends, Sunday evening.

I met one of my friends, Sunday.

^{†That is, along the space-time continuum.}