Pronouns
Pronouns, as you might remember, are words that stand in for nouns or proper nouns. But beyond the standard personal pronouns - 'he,' 'she,' 'him,' 'ours,' 'theirs,' etc. - there are many other pronouns that make up our basic syntax. Pronouns that introduce dependent clauses for instance (which are called relative pronouns), pronouns that turn back on themselves (which are called reflexive pronouns), pronouns that help us ask questions (interrogative pronouns) and pronouns that show ownership (which are possessive pronouns) - just to name a few.
I really want to make pronouns interesting, but I can't do it on my own, so here's Gary. Gary has graciously agreed to dress up in our Grammar Gorilla suit for the duration of this video to help illustrate pronouns. Gary's in between jobs right now, and our budget's tight, so he agreed to be paid in sandwiches. Banana sandwiches. (Because he's a gorilla, get it?) You ready, Gary? We forgot to put mouth holes in the suit, so Gary might be a little hard to hear. You'll just have to pay attention!
Relative Pronouns
Relative pronouns help connect the main clause of a sentence to a clause that adds detail or helps describe the main clause, called a relative clause. The relative pronouns are 'who'/'whom,' 'whoever'/'whomever,' 'whose,' 'that' and 'which.' First, let's look at 'who' and 'that.' In proper English writing, 'who' should only be used when referring to people -- that is, other human beings.
So, Gary, who we found on the street outside the studio, will be playing the part of the gorilla today.
We use 'who' here, as we're describing something about Gary the person (the relative clause adds the detail of where we found him). Whereas in the following sentence, we would use 'that,' as the subject the pronoun relates to is no longer definitely a person (poor Gary!).
'Hey Mel, is that the gorilla that you ordered?' the director asked. 'Throw it in the cage with the other monkeys.'
Because English is weird, 'whose' is the only possessive relative pronoun, and it can be used for both people and things despite having 'who' in it.
So, The actors, whose contracts strictly forbid them from performing alone with animals, couldn't help Gary. and The gorillas, whose handlers were out to lunch, didn't notice Gary there either. are equally correct.
Now, in many cases, both 'that' and 'which' seem like they would fit. But there is one important distinction: 'That' should only be used when introducing a clause that adds necessary and essential information to the sentence (called a restrictive clause), while 'which' is used when introducing information that adds non-essential detail (called a non-restrictive clause). The thing you most need to remember here is necessary and essential detail compared to non-essential detail.
The largest of the gorillas in the cage, which looked about eight feet tall, sidled over to Gary.
'Which' introduces the clause that adds the detail that the gorilla in the cage 'looked about eight feet tall.' This is non-restrictive because the sentence can function just fine without it, i.e. The largest of the gorillas in the cage sidled over to Gary. Now take this sentence:
This is not the situation that I'd hoped to be in, Gary thought to himself.
'That' introduces a restrictive relative clause here because 'I'd hoped to be in' cannot function on its own - it's an incomplete sentence - and it adds detail necessary to make the full sentence make sense. 'Which' can also be used to introduce a restrictive relative clause but only when it is the object of a preposition. That is to say, a preposition precedes it - as in 'in which,' 'to which,' 'through which,' or: The scene in which the Grammar Gorilla was supposed to appear was canceled at the last minute, for instance.
Who and Whom
That whole 'object of a preposition' thing also applies when you need to figure out whether to use 'who' or 'whom' in a sentence. Now, the reality is unless you really love grammar (and some of you do, like Gary, our Grammar Gorilla . . . Where is Gary?), the reality is that you rarely use the word 'whom' when you're speaking or writing informally. But for formal writing, you should at least know when to use it before deciding that you think it's too stuffy or uptight (and your teacher might require you to use it).
Okay, so, just like 'which,' use 'whom' whenever a preposition precedes the word. In other words, the correct grammatical construction is always 'for whom' and never 'for who', likewise 'for whoever' and 'for whomever.' You'll also want to use 'whom' or 'whomever' whenever it's the object of the verb of a sentence or clause in general.
Gary, whom I barely knew, was missing.
'Whom I barely knew' is a non-restrictive clause, with 'I' as the subject, 'knew' as the verb and 'whom' as the object of that verb (referring to Gary).