Commonly confused words:  Who(m), Which, and That

1.  Who, whom, whose

•  Use who, whom, or whose to refer to a person or persons.

            Examples

            
                 Who is the correct pronoun since it is the subject of live
                  in the clause who live in glass houses.

            
                   Whom is the correct pronoun since it is the direct object of
                    married in the clause whom she married.
                 

            
                    Whose is the correct pronoun since it indicates possession of the car.

• Who, whom, or whose may introduce either an essential or a nonessential clause.

        A clause is essential if it is needed  in the sentence to identify the noun it is describing.
        Do not separate an essential clause from the rest of the sentence with commas.

           Examples

        A clause is nonessential if it is not needed in the sentence to identify the noun it is describing.
        Do separate a nonessential clause from the rest of the sentence with commas.

            Examples

2. That, which

• Use that and which to refer to nonhuman entities (things, ideas)

          Use that to introduce an essential clause (do not set off the clause with commas).

              Examples

          Use which to introduce a nonessential clause (do set off the clause with commas).

              Examples

Link to exercise on who / that / which.