Speaking of who/whom, here’s a pronoun case chart from cengage.
I assume it’s from the textbook Evergreen: A Guide to Writing by Susan Fawcett.
Personal narrative: I saw a pronoun case chart for the first time in my life when I started teaching freshman composition. Up to that moment, I had no idea what the grammatical distinction was between who and whom; I certainly had no clue what the word “case” might mean, or what part of grammar it applied to.
The chart was a revelation.
Interestingly, I discovered that in fact I did know the distinction unconsciously, deep down in my basal ganglia, where grammar resides. I had picked it up in spite of the fact that whom has been dead for a century.
My basal ganglia knew the dead-for-a-century business, too.
Grammar brain knows.
The basal ganglia are much smarter than we give them credit for, but that is a subject for another day.