USING SUBJECT PRONOUNS: WHO, WHICH, THAT

I thanked the woman. She helped me.
(a) I thanked the woman who helped me.
(b) I thanked the woman that helped me.

The book is mine. It is on the table.
(a) The book which is on the table is mine.
(b) The book that is on the table is mine.

In (a): I thanked the woman = an independent clause, who helped me = an adjective clause
The adjective clause modifies the noun woman.

In (a): who is the subject of the adjective clause.
In (b): that is the subject of the adjective clause.
Note: (a) and (b) have the same meaning.

who = 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