Grammar:

Relative, Restrictive, and Nonrestrictive Clauses

Relative Clause

This is a clause that generally modifies a noun or a noun phrase and is often introduced by a relative pronoun (which, that, who, whom, whose). A relative clause connects ideas by using pronouns that relate to something previously mentioned and allows the writer to combine two independent clauses into one sentence. A relative clause is also known as an adjective clause. There are two types of relative clauses: restrictive and nonrestrictive.

Here are a few examples:

• The book that she read was important for her literature review. (restrictive)
• The participants who were interviewed volunteered to be part of the study. (restrictive)
• Walden University, which is entirely online, has main administrative offices in Baltimore and Minneapolis. (nonrestrictive)

Relative Pronouns

* In APA 7, per Section 4.19, use "who" or "whom" instead of "that" when referring to a human.

** Although both "which" and "that are grammatically correct in restrictive clauses, APA prefers "that" for restrictive clauses. See APA 7, Sections 4.19-4.21 for more information on this topic.

• Take this quiz on Grammar Diagnostic Quiz to test your understanding of relative pronouns.
• Use relative clauses to create more sentence variety.

Restrictive Clause

A restrictive clause restricts or defines the meaning of a noun or noun phrase and provides necessary information about the noun in the sentence. It is not separated from the rest of the sentence by commas. Restrictive clauses are more common in writing than nonrestrictive clauses. A restrictive clause is also sometimes referred to as an essential clause or phrase.

Here are a few examples:

• The student who sits in the back of the room asks a lot of questions.
• The results that I obtained may invoke positive social change.
• The journalist whose story I read yesterday has won prizes for her work.

When the relative pronoun functions as the object of the sentence, it can (and usually is) omitted from the relative clause.

Here are a few examples:

• The results that I obtained may invoke positive social change.
• The article that I requested did not arrive on time.
• The participants who I interviewed met me at the local library.

Nonrestrictive Clause

A nonrestrictive clause adds additional information to a sentence. It is usually a proper noun or a common noun that refers to a unique person, thing, or event. It uses commas to show that the information is additional. The commas almost act like parentheses within the sentence. If the information between the commas is omitted, readers will still understand the overall meaning of the sentence. A nonrestrictive clause is also known as a nonessential clause or phrase.

Here are a few examples:

• I want to thank my father, Mark Smith, for all of his love and support.
  • With the nonrestrictive clause omitted: I want to thank my father for all of his love and support.
• The hypothesis, which I tested throughout the research, was rejected.
  • With the nonrestrictive clause omitted: The hypothesis was rejected.
• I have found the article, which I have been looking for.
  • With the nonrestrictive clause omitted: I have found the article.

Although "that" is sometimes used in restrictive clauses, it is not allowed in nonrestrictive clauses.

• CORRECT: Minneapolis, which has a population of about 400,000, is the largest city in Minnesota.
• INCORRECT: Minneapolis, that has a population of about 400,000, is the largest city in Minnesota.
   
• CORRECT: I had to fix my printer, which I bought less than a year ago.
• INCORRECT: I had to fix my printer, that I bought less than a year ago.

A relative pronoun cannot be deleted in a nonrestrictive clause.

• CORRECT: Minneapolis, which has a population of about 400,000, is the largest city in Minnesota.
• INCORRECT: Minneapolis, has a population of about 400,000, is the largest city in Minnesota.
   
• CORRECT: I had to fix my printer, which I bought less than a year ago.
• INCORRECT: I had to fix my printer, I bought less than a year ago.

In academic writing, relative clauses are often reduced for a more concise style. This also creates more sentence variety. When reducing a relative clause, it is necessary to delete the relative pronoun and either delete or change the verb. Here are some examples:

• Gun control is a controversial issue that is about personal rights. ("be" + prepositional phrase)
• The steps that were followed were explained in the Methods section. (passive)
• Other researchers who are exploring the same topic have discovered similar solutions. (progressive verb tense)
• Participants who were available to meet in my office completed their interview there. ("be" + "-able" adjective)
• Some of the subjects lived in urban areas that had with high crime rates. ("have" as a main verb is replaced by "with")
• In this paper, I reviewed many research articles that addressed addressing the topic of gun control. (linking verbs or verbs describing facts can be changed to "–ing" clauses)
• The changes that are to be implemented with the new curriculum revisions are outlined in the handout. ("to" clauses)