Grammar and Mechanics:

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.

Note the italicizing and highlighting used for emphasis in the examples on this page.

Here are a few examples:

• The article that I read was important for my 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

Type of relative clause	Referring to a human	Referring to something other than a human	Possessive
Restrictive	who, whom, that *	which, that **	whose
Nonrestrictive (with commas)	who, whom	which	whose

* Per APA 7, Section 4.19 and 4.20, 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, Section 4.21 for more information on this.

Use relative clauses to create more sentence variety.

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 results that I obtained may lead to positive social change.
  • The clause that I obtained makes it clear which specific results are being referred to.
• The participant who met me at the coffee shop asked a lot of questions.
  • The clause who met me at the coffee shop specifies which participant asked a lot of questions.
• The researcher whose article I read yesterday has won prizes for her work.
  • The clause whose article I read yesterday specifies which researcher.

A nonrestrictive clause adds additional information to a sentence. It is usually 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 couple examples:

• The hypothesis, which I tested throughout the research, was rejected.
  • With the nonrestrictive clause omitted: The hypothesis was rejected. This means that there was only one hypothesis, and the reader already knows what hypothesis was being referred to.
• I collected participants' responses via e-mail conversations, which have the advantage of not requiring recording and transcriptions.
  • With the nonrestrictive clause omitted: I collected participants' responses via e-mail conversations.

Although that is often 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 received permission from the study site to contact possible participants, which I had requested 2 months prior.
• INCORRECT: I received permission from the study site to contact possible participants, that I had requested 2 months prior.

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 received permission from the study site to contact possible participants, which I had requested 2 months prior.
• INCORRECT: I received permission from the study site to contact possible participants, I had requested 2 months prior.

Often the choice to use a restrictive or nonrestrictive clause lies with the writer and the intended meaning of the sentence. Consider the following examples:

Restrictive: The employees who work remotely requested further training.

• This means that only some of the employees work remotely. This group of employees requested more training.

Nonrestrictive: The employees, who work remotely, requested further training.

• This means that all the employees work remotely and, therefore, all the employees requested more training.

Restrictive: The participants who were given the opportunity to do member checking did not make any changes to their interview scripts.

• This means that only some of the participants were given the opportunity to do member checking. Those who did the member checking did not make any changes to their interview scripts. 

Nonrestrictive: The participants, who were given the opportunity to do member checking, did not make any changes to their interview scripts.

• This means that all the participants were given the opportunity to do member checking, and no changes were made to the interview scripts.

Restrictive: The article that I found through Business Source Complete served as the baseline for my doctoral study.

• This means that only one article was found through Business Source Complete, and it was this particular article that was the baseline for my study.

Nonrestrictive: The article, which I found through Business Source Complete, served as the baseline for my doctoral study.

• The focus here is on the article itself. Extra information is provided about where the article was found, but this information is not essential to the meaning of the sentence. Other articles may also have been found through Business Source Complete.

When the relative pronoun (that, which, who, whom, whose) functions as the object of the verb in the relative clause, it can be (and usually is) omitted. Although its use here is not strictly wrong, deleting it from the relative clause creates a more concise sentence.

Here are a few examples:

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

Relative clauses can also be reduced to phrases to create more sentence variety. When reducing a relative clause, it is necessary to delete the relative pronoun and to either delete or change the verb.

Here are a few more 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 voice)
• 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+ adjective)
• Some of the subjects lived in urban areas that had with high crime rates. (have as a main verb is replaced by the preposition with)
• In this dissertation, I reviewed many research articles that addressed addressing the topic of gun control. (linking verbs or verbs describing facts can be changed to –ing phrases)
• The changes that are to be implemented with the new curriculum revisions are outlined in the handout. (infinitive phrase—i.e., to+ verb)