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Relative Clauses

This handout will allow you to see how important ideas can be combined with relative clauses to help you subordinate less important ideas and add variety to your sentences. First, it’s important to know that a relative clause is a special type of dependent clause that usually functions as an adjective modifying a noun or pronoun within the main clause. Sometimes it can serve as an adverb when it begins with when or where.

Subordinators for Relative Clauses

There are eight subordinators for relative clauses: who, whom, whose, which, that, where, why, and when. These subordinators (called relatives and shown below in square brackets) are unique. They do two things at one time. They connect the dependent clause (in parentheses in the examples below) to the main clause. At the same time each functions as a subject, object, adjective, or adverb within the dependent clause.

An object ([that] weighs five pounds on earth) would weigh two pounds on the planet Mercury.

The relative clause modifies object.

All men ([whom] citizens of the United States have elected as president) have been native-born.

The relative clause modifies men.

Mark Twain, ([whose] real name was Samuel Clemens), grew up in Hannibal, Missouri.


The relative clause modifies Mark Twain.

Airplane-passenger service was begun on May 3, 1919, ([when] a pilot flew two women to New Jersey).


The relative clause modifies was begun.

At the common meeting point of Utah, Colorado, Arizona, and New Mexico is a spot ([where] a house could be built with each of its corners in a different state).

The relative clause modifies spot.


Nonrestrictive vs. Restrictive Relative Clauses and Phrases

You may have noticed in the previous examples that some relative clauses and phrases require commas while others don’t. Commas indicate that the relative clause is not really needed in order to understand the sentence. The absence of commas indicates that the relative clause is needed in order to understand the sentence. We will first look at clauses that are set off with commas.


Nonrestrictive Relative Clauses and Phrases

Commas set off a nonrestrictive relative clause or phrase, that is, a clause or phrase that is not really needed to identify the noun being modified. In the following example, the clause who was assassinated in 1963 adds some information about the modified noun, John F. Kennedy, but even without this extra information we would understand who he is. In other words, when we leave off the relative clause, the sentence still makes good sense.

John F. Kennedy, who was assassinated in 1963, was the first Catholic president.
John F. Kennedy was the first Catholic president.

Note: A comma must be put before and after the nonrestrictive clause or phrase, unless of course it is at the end of a sentence, in which case the comma comes only before the non-restrictive clause.


Only two types of nouns are followed by nonrestrictive clauses or phrases: proper nouns and nouns already familiar to the reader.

The following are examples of nonrestrictive clauses or phrases.

I went to the movies last night. The movie, which was about Ghandi, was fascinating.

The highest mountain in the world, Mount Everest, is located in Asia.

Tennis, which is a popular sport, is not difficult to learn.


Restrictive Relative Clauses and Phrases

The relative clause or phrase called restrictive when it is needed to understand which specific person or thing the modified noun is. A restrictive clause is not set off with commas. These clauses “restrict” or “limit” the meaning of the nouns they modify. They tell you which one and make the meaning specific. Relative clauses that begin with that are always restrictive; they should not be set off by commas.

The man who came by yesterday is my professor.

The man is my professor.

(Which man? Without the relative clause, we don’t know which man.)