I have a question about the preposition that comes before "years."

When you have a swallow nest around your home and the swallows don't seem to come back every spring/summer, which sentence can you use?

In some years the swallows returned; in others they didn't.

On some years the swallows returned; on others they didn't.

  • 1
    Good things happen in good years, months, or weeks (or specifically in 2020, in September, etc.), but on good days or dates (or specifically on Saturday, on the 20th of September, etc.). Sep 17, 2021 at 11:39

2 Answers 2


As a general rule, we use "in" for months, years, centuries and long periods, and "on" for days and dates. However, there are exceptions.

It all depends on how specific you want to be. Obviously, years comprise of days; days comprise of hours and minutes etc. For example, you might be talking about something that could occur on any day within a month, so you would use "in":

I went swimming 10 times in a month.

However, if 'months' were the ultimate unit (ie there is no need to be specific about any smaller unit of time), you might use "on":

I visit my parents on alternate months.

Your example is about past data, and seemingly about something which occurs only once per year (if at all). Arguably, you could use either, because you are talking about something that occured within certain years, but on the other hand you are comparing years as whole units of time.

Alternatively, you could use neither:

Some years, the swallows returned; other years, they did not.

  • Regarding the repeated use of "comprise of": Consider "comprise" or "are composed of". There are those who argue that using "comprised of" to mean "composed of" should be considered ok (and many who find it annoying, as it reverses the direction of the primary meaning) but almost no one thinks "comprise of" is correct. E.g. the usage note at the bottom of lexico.com/definition/comprise says "the construction comprise of, as in the property comprises of bedroom, bathroom, and kitchen, is regarded as incorrect."
    – Jacob C.
    Sep 17, 2021 at 20:14

A year is a unit of time and when placing some event within it you use the preposition "in" instead of "on".

So your first sentence is correct. Another way of saying it might be:

During some years the swallows returned; during others they didn't.

But between "in" and "during" it's a preference in my opinion.

I'll note that there are some English speakers who use "on" where "in" may be more appropriate but I believe they are in the minority.

I have heard some people use "on" such as:

I had to wait on line for 2 hours to get through airport security.

Where I suggest that:

I had to wait in line for 2 hours to get...

is more common.

It's possible your usage examples fall into the same category.

You can get "on" an airplane but you also get "in" it but "on" is the more commonly understood term here. You can get "in" a line but getting "on" one implies to me that you are somehow on top of the line.

  • English Language Learners is absolutely the WORST StackExchange forum for "experts" who simply downvote answers without any explanation! Doing so helps absolutely nobody.
    – jwh20
    Sep 17, 2021 at 10:42
  • 2
    I think you'll find that's a problem all over Stack Exchange. not just here. The reason I downvoted it because the first part of your answer is wrong - see my answer for an example of where you could use either "in" or "on" with the same unit of time. And the second part of your answer is opinion-based. "In my opinion" is not something we should read here, at least in direct answer to a question.
    – Astralbee
    Sep 17, 2021 at 11:14

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