Consider the following example: “In making his choice, Otto Frank had to bear several points in mind.”

You see, there is no particular pattern that helps me decide whether I have to use “on” instead of “in.”

Could I use “On making his choice, Otto...” instead?

Also, I know they are occasions where “on” should be used instead of “in.” For instance, we have: “on entering the room, she saw him.”

So, that is the problem. I do not see any distinctive pattern that helps me identifying which one of them I have to choose.

3 Answers 3


Hopefully you are aware of the most basic meanings of "in" and "on".

  • "In" - means that something is between, within, or inside other things.
  • "On" - means that something is atop of something else.

When used in connection with a timeline, as a general rule we say "in" to refer to something that happened between other events, and "on" to refer to something that happened at the same time as another event. If you don't instinctively know which to use, try considering the wider implication of what you are saying.

Take your first example:

In making his choice, Otto Frank had to bear several points in mind.

"Making a choice" is a process. You may think about and consider various things over a period of time. So, the points he had to bear in mind appeared within that process, so "in" is appropriate.

Your second example (slightly changed):

On entering the room, he noticed her.

Entering the room is an event, and as soon as he was in the room, he saw her. They happened at the same time, so "on" is appropriate.

  • Another way to think about this usage is that "in" talks about how and "on" talks about when.
    – Era
    Commented Oct 9, 2019 at 15:06
  • 2
    I think we tread on thin ice when we try to link idiomatic meanings of prepositions back to what you call their "most basic" meanings. Your answer might cause a learner to wonder why we say things like, "He had something heavy on his mind," or, "That event has been on her mind a lot these days," or why Ray Charles once crooned, "Just an old sweet song keeps Georgia on my mind." I think the real reason we use in instead of on in the OP's sentence is because the normal expression just happens to be bear in mind, not bear on mind, much like keep in mind or stay on track.
    – J.R.
    Commented Oct 9, 2019 at 18:01

Also, you can different between (on) and ( in) by the meaning sentences, it depends on it. Both of them are prepositions and locate the place of the things.


They seem to me to be idioms that have the same meaning but are used in slightly different situations.

"On mind" is used in expressions such as "What's on your mind?" or "I've got you on my mind."

On the other hand, "in mind" is used in "Did you have something in mind?" or "I'll keep you in mind."

Based on these examples, "on mind" seems to be used chiefly when you have something between "on" and "mind." But "in mind" can also be used like that, in the case of something like "In my mind, I imagined that you'd like the gift a lot more."

So, "on mind" is when something is "on your/my/etc mind." "In mind" can be both. (Although I fail to think of a situation where someone would say "In your mind.")

Longman Dictionary of Contemporary English also has "on mind" to be written as "on your/somebody's mind."

on your/somebody’s mind

a) if something is on your mind, you keep thinking or worrying about it

He looked as though he had something on his mind.

Sorry I forgot. I’ve got a lot on my mind (=a lot of problems to worry about) at the moment.

b) if something is on your mind, that is what you are thinking about She’s the type of person who just says what’s on her mind

Merriam Webster Dictionary writes "in mind" to be "to have (someone or something) in mind."

have (someone or something) in mind - idiom

: to be thinking of (someone or something): such as

1 : to be thinking of choosing (someone) for a job, position, etc.

They have you in mind for the job.

2 : to be thinking of doing (something)

"I'd like to do something special for our anniversary." "What sort of thing did you have in mind?"

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