How to decide which relative pronoun you have to use

Read the following sentence:

This is the person (           ) gave me hard assignments last year.

To find out which relative pronoun, you may rely on the following table.
1) First, check whether the antecedent is a human being or not.
2) Next, you need to check whether the dependent clause following the antecedent is essential or not. Close your eyes and imagine "the person." You may draw any kind of person in your mind.
Now draw the person who gave you hard assignments last year.
This image is more specific than the person you drew.
So the clause that follow the antecedent is essential since it narrow down the person this sentence is referring to.
3) Now you have to determine whether you need the relative pronoun as a subject, object or possessive. Since we need a subject, a subject of the verb "gave" in this sentence, you will need "who."

Relative Pronouns
     Human beings     Nonhuman beings
   Essential  Nonessential  Essential Nonessential*
 subject  who , who that , which
 object  (whom) , whom (that) , which
 possessive  whose , whose whose , whose

Sentential relative pronouns (relative pronouns that have an entire sentence as an antecedent) use these nonessential pronouns.


Some people equate "essential" to "restrictive" and "nonessential" to "nonrestrictive."

   Essential (restrictive) Nonessential (nonrestrictive)
 antecedent an antecedent that is not specifically defined, such as a house, the house, so that readers might ask "which house?"  In most cases, an antecedent that is specifically defined so that readers could have a clear idea about which the writer refers to, such as this building, Lisa Morei and the Fine Arts building
 dependent clause following the antecedent  gives information that will further define the antecedent in readers' mind  provides interesting -- even highly relevant -- information, but the information is not used to
further define the antecedent
 form the dependent clause stand closely next to the antecedent (not set off by a comma)  The dependent clause is set off by a comma, which gives an impression to the reader that the dependent clause could be pulled out.

 antecedent (singular)  any individual

 The girl whom I once hated gave me a birthday card.

The community college I attended was good.

The lawn mower that is broken is in the garage.

 a specific individual (proper name: Tom, Elon College), an abstract entire group

 My cousin Amy, who is getting married, asked me to be at her wedding.

The community college, which is usually run by the local government, is good.

The lawn mower, which is broken, is in the garage.

 antecedent (plural)  only part of the group in general  Reporters who do not read the stylebook should not criticize their editors.
 all the group in general  Reporters, who do not read the stylebook, should not criticize their editors.
   The dependent clause is not used to define the antecedent further.

 We purchased a gun, which is on sale.

We purchased a gun that is on sale. (seeking a bargain gun)

   The antecedent is specific in context  She headed north from Mexico in a car that had more than 130, 000 miles showing on its odometer. The car, which had New Jersey license plates, was quickly spotted by police in Texas.
 sentential relative pronoun  which does not refer to a specific noun but to the whole idea of the brakes fading badly  On all three test models the brakes faded, which indicates a need for a redesign of this model's braking system.