Restrictive & Nonrestrictive Elements

Restrictive element--a word, phrase, or clause that limits the essential meaning of the sentence element it modifies or provides necessary identifying information about it. The restrictive element is not set off from the element that it modifies with commas, dashes, or parentheses.

 Nonrestrictive element--a word, phrase, or clause that gives additional information about the preceding part of the sentence but does not restrict or limit the meaning of that part. A nonrestrictive element is not essential to the sentence; it can be deleted without changing the sentence's basic meaning. As an indication that it is not essential, it is always set off from the rest of the sentence with a comma before it and, if it is in the middle of the sentence, after it as well.

To decide whether an element is restrictive or nonrestrictive, mentally delete the element, and then decide whether the deletion changes the meaning of the rest of the sentence or makes it unclear. If it does, the element is probably restrictive and should not be set off with commas. If it does not, the element is probably nonrestrictive and requires commas.

Restrictive: Students who neglect to complete their assignments will receive failing grades. Nonrestrictive: The two neglectful students, who did not complete their assignments, will receive failing grades.
 
 

Adjective and adverb clauses

An adjective clause begins with who, whom, whose, which, that, when, where, or why . Adverb clauses begin with subordinating conjunctions like because, although, or before. They are usually essential to the sentence and are not set off with commas unless they precede the independent clause or unless they begin with conjunctions expressing the idea of contrast like although, even though, or while.

• I feel at home in the Woodruff Library, which is where I spend most of my time.
• The claim that men are more intelligent than women is a myth.

Participial phrases and prepositional phrases

Prepositional phrases are usually restrictive but sometimes not essential and are therefore set off by commas. Participial phrases may be either restrictive or nonrestrictive.

• Suzy, amazed at the horns growing out of her professor's head, stared at the oddity.  
• A penny saved is a penny earned.  
• The student, despite ill health, came to class.  
• Writing with creativity produces more interesting papers.

Appositives

An appositive is a noun or noun substitute that renames a nearby noun. When not essential (restrictive), it is set off with commas.

• In the one class in which I fell asleep, chemistry, we had a pop quiz.  
• The playwright Shakespeare wrote many plays.

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