USING OBJECT PRONOUNS: WHO(M), WHICH, THAT

The man was Mr. Jones. I saw him.
(a) The man who(m) I saw was Mr. Jones.
(b) The man that I saw was Mr. Jones.
(c) The man -- I saw was Mr. Jones.

Notice in the examples: The adjective clause pronouns are placed at the beginning of the clause. (General guideline: Place an adjective clause pronoun as close as possible to the noun it modifies.)

In (a): who is usually used instead of whom, especially in speaking. Whom is generally used only in very formal English.

The movie wasn't very good. We saw it last night.
(a) The movie which we saw last night wasn't very good.
(b) The movie that we saw last night wasn't very good.
(c) The movie -- we saw last night wasn't very good.

In (c): An object pronoun is often omitted from an adjective clause. (A subject pronoun, however, may not be omitted.)

who(m) = used for people.
which = used for things.
that = used for both people and things.


Cheers!
Naeem

Source(s):
Understanding and Using English Grammar by Betty Schrampfer Azar