They sound the same to me. Are they interchangeable?

I hear people say "in a group," but when I use it in my writing, the auto-correct changed it to "of a group." I checked the grammar book and think they are both grammatical, so I'm wondering if there is a difference between these two.

For example:

Please notify the members in your group or the members of your group


There is a difference in meaning but in most cases it is a very subtle one. In denotes that you/they/that is "part of something", whilst of denotes "belonging to something"

in preposition (PART): forming a part of something:

He used to be the lead singer in a rock band.


of preposition (POSSESSION); used to show possession, belonging, or origin:

employees of the company


Please notify the members in your group = Please notify the members who are part of your group

Therefore this does not necessarily include all members


Please notify the members of your group = Please notify the members who belong to your group

Whilst this would inherently include all members

  • 1
    Common use is belong to a or "of" a group; Example "Quickly list all groups a user is member of or owner of in Office 365"
    – Brad
    Mar 11 at 9:05

"members of a group" is more idiomatic for referring to a group of people as a whole. Other similar expressions include "employees of a company," "members of Congress," or "citizens of a country."

"members in a group" would be more commonly used in cases like "there should be 3 members in a group."


For me personally, in this situation members of a group feels more like something people have been assigned to, something they belong to - a status you're talking about in a more general sense.

Members in a group carries more of an immediate, dynamic feel - like the group is actually doing something together, actively working on something, or several people have physically formed a group by coming together. It feels more like you're describing a specific situation, rather than a category people have been assigned to, if that makes sense.

It's really a (subjective) tonal nuance - of and in both carry the same idea in this context, and are interchangeable outside of a few common phrasings (e.g. several people together are in a group, of a group works but probably sounds unusual to most people).

In is also a preposition for actual physical location, so in some contexts (where an organisation is also a place) it might be unclear which meaning you're going for:

  • There are 50 members of this gym - 50 people have joined this gym

  • There are 50 members in this gym - 50 of the people who have joined (there may be more!) are inside this gym right now

I think that's partly why in feels more immediate in general, it carries that same sense of "the situation right here, right now", whereas of can sound more distant and abstract.

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