In Chinese, using "们" after a noun is, in some sense, equivalent to adding an "s" after an English word. Yet I find the rules in Chinese of using 们 to be very puzzling; I am a native speaker yet I couldn't figure this out when a good friend of mine asked me when to use 们 and when not to.
I can come up with a few examples:
Looks like a 们 is needed in this case. Yet, in
...it sounds awkward if there is a 们 after 同学.
If anyone could come up with a rule that's easy to follow and applies to most cases, that would be very helpful, especially to non-native speakers like my friend.