Hello good people of EnglishForward.com,
The distinction between who and whom is in theory relatively easy, but there are many cases where I'm left to wonder as to what the correct answer is.
I've done some superficial research and have realized that many of the problematic sentences are of the same structure, apparently referred to as (non-)defining relative clauses.
Consider the next sentence:
"A 24-year old Gambian failed asylum-seeker, who Mann had apparently taken in to help him avoid deportation, was arrested on Thursday."
(I think this is a defining relative clause.)
Some of the websites that I've visited mention that who/whom are both applicable. For example:
https://www.ego4u.com/en/cram-up/grammar/relative-clauses lists:
"Jim, who/whom we met yesterday, is very nice."
In my example sentence above, I was convinced that it should be whom because I believe Mann is the subject of that relative clause. Mann had taken HIM in to help HIM avoid deportation.
But maybe both who/whom are possible as explained in the sentence with Jim.
Thanks a lot for your help!