THE STRUCTURE OF RELATIVE CLAUSES

A relative clause always immediately follows the noun it modifies. Like all clauses, relative clauses have a subject and a verb. The relative pronoun may be the subject of the clause, but it isn’t always.

                      (Main noun)       (Rel. Pro)I ate the ice cream that was in the freezer.
                                              (Subj)    (Verb)

                           (Main Noun)   (Rel. Pro)I didn’t eat the pie that you were saving for tonight.                                                          (Subj)        (Verb)

        A relative pronoun is usually the first...

word of a relative clause; however, in some cases the pronoun follows a preposition:

        We have many blessings for which we are deeply grateful.

Additionally, when the relative pronoun is not the subject of the relative clause, it may be omitted entirely (especially in spoken English):

        I didn’t eat the pie you were saving for tonight.

When the pronoun is the subject, it cannot be omitted:

        *I ate the ice cream was in the refrigerator.

TYPES OF RELATIVE CLAUSE

        There are two types of relative clause. Both types modify nouns, but the first type makes a noun more specific, while the second type adds extra facts or information about a noun. It’s important to understand these two types of relative clause because they not only differ in meaning, but they are punctuated differently and often use different relative pronouns.

Type 1--Clauses That Make Nouns Specific

        Women who work are happier than women who don’t work.

        In the above sentence, the relative clauses who work and who don’t work are used to make the noun women more specific. This type of relative clause changes the meaning of the noun it modifies.
        Women who work and women who don’t work are two different groups of women. Without the appropriate relative clauses, this meaning would not be clear:

        *Women are happier than women.

This type of relative clause is sometimes called a Restrictive Relative Clause because it restricts or limits the meaning of a more general noun. Women who work is more restricted than the general noun women.

Here are some additional examples of sentences that show how a relative clause can change the meaning of a noun.

Students learn a lot.
Students who ask questions learn a lot.Teachers are unpopular
Teachers who give a lot of assignments are unpopular.

Type 2--Clauses that Add Information

        Going to the movies, which I love to do, can be very expensive.

        In the above sentence, the relative clause which I love to do is used to say something extra about going to the movies, but it does not change the meaning of that phrase.
        If this clause were removed, the basic meaning of the sentence would be unchanged.
Going to the movies can be very expensive.
This type of clause is sometimes called an Unrestricted Relative Clause since the meaning of the noun it modifies is not restricted or limited by the clause.
Here are some more examples of relative clauses that add information. Note that although these clauses don’t change the basic meaning of the sentences, they do make the sentences more detailed.

Hunter college is part of the City University of New York.
Hunter College, which is located at 68th and Park, is part of the City University of New York.Creativity is a quality all human beings have.
Creativity, which may take many forms, is a quality all human beings have.

CHOOSING A RELATIVE PRONOUN

        The three most common relative pronouns are who, which, and that.
        The choice of pronoun depends upon the noun the clause refers to and on what type of relative clause is used.
Who

--refers to a person or people.
--may be used with a clause that makes a noun specific
--may be used with a clause that adds information

People who live in New York lead very busy lives.
My sister, who works for the YMCA, leads a very active life.

Which

--refers to a thing or concept
--is most often used in clauses that add information
--is sometimes used in a clause that makes a noun specific ( usually when a speaker or writer wants to sound more formal).        The Empire State Building, which used to be the tallest building in the world, is still a popular tourist attraction.
        The lessons which we have learned are no more important than the lessons which we have yet to learn.

That

--is used only in clauses that make a noun more specific
--most often refers to a thing or concept
--is sometimes used to refer to a person or people, (usually only in informal writing or in speaking)

The book that you gave me is lost
The kid that I babysit threw your book in the trash.

        Note: Some people consider that inappropriate when referring to people although most writers and speakers use it quite naturally. If you wish to be formal, always use who for a person or people:

The child who threw your book away was only three years old.

Where and When

--are used for a clause that refers to a place or time 
--may be used for clauses that make a noun more specific
--may be used for clauses that add information

        New York is a place where people of many different cultures live and work together.
        New York City, where millions of immigrants live, is sometimes called a Melting Pot.

        The 1960's was a time when many Americans began to question the actions of their government.
In the 1970's, when many new rights and freedoms had been gained, people began to lead quieter, more private lives.

Choosing between Who, Whom, and Whose

Like most pronouns in English,
ex.	I he we	me him us	my his our

the relative pronoun who has more than one form

Who -- for the subject of a clause Whom--for the object of a verb or preposition Whose-- for a possessive noun
The form of who in a relative clause must change depending on whether it’s the subject, object, or possessive.
As a Subject
        I know a woman who has two children.
In this sentence, who replaces woman as the subject of the verb has (A woman has two children)
As an Object
        My friend has two children, whom she loves very much.
In this sentence, whom replaces children as the object of the verb loves (She loves the children)
As a Possessive
        The older one is a boy, whose name is Jonathan
In this sentence whose replaces the noun boy as a possessive noun (the boy’s name is Jonathan).
As an Object of a Preposition
        Jonathan has a little sister, with whom he plays all the time.
In this sentence, whom replaces the noun sister as the object of the preposition with (he plays with his sister).


        Note: In a standard sentence, the preposition and its object normally come after the verb, but because the relative pronoun always comes at the beginning of a relative clause, it is a convention to place the preposition at the beginning of a relative clause in formal writing, as in the example above. Often, however, when speaking or in informal writing, the preposition comes after the verb of a relative clause.

        Jonathan has a little sister, whom he plays with all the time.