Punctuation: Use Commas to Set Off Nonrestrictive Clauses

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.

More examples:

1. Steven Strom, whose show you like, will host a party next week. (nonrestrictive)
2. John, who spent the last three days fishing, is back on the job again. (nonrestrictive)
3. The gentleman who is standing by the fireplace is a well-known composer. (restrictive)

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Exercise:

Add commas:

• My niece who was running around the room had too much sugar earlier.
• The boat that sailed on October 25 is the one to which we referred in the contract.
• I scolded my niece who was misbehaving this morning.
• Like Water for Chocolate which was an excellent book was made into a movie.
• Barcelona which I visited last year has a lot of interesting architecture.
• Posey’s Cafe which Chester recommended is a fantastic restaurant.
• Our ability to use language is one of the things that set us apart from animals.
• For camp the children need clothes that are washable.
• The 1964 Ford Mustang which propelled Lee Iacocca to the top of the automobile industry is now considered a classic.
• The child who is running around the room is my niece.
• I bumped into the child who was running around the room.
• The suspect in the lineup who owns a red car committed the crime.
• The book that I finished reading yesterday was really fascinating.
• I just finished reading a book that was fascinating.
• I finished reading Like Water for Chocolate which was made into a movie.
• The city that I want to visit the most is Shanghai.
• Professor Shevchenko who is my teacher has been at this college for 25 years.
• Shanghai was the best city that I visited in all of Asia.
• The store honored the complaints that were less than 60 days old.
• For camp the children need sturdy shoes, which are expensive.
• My wife whom I love dearly is a brilliant physicist.
• The suspect in the lineup who has red hair committed the crime.
• The study was limited to US citizens who have never been to Canada.

Answers:

• My niece, who was running around the room, had too much sugar earlier.
• I scolded my niece, who was misbehaving this morning.
• The boat that sailed on October 25 is the one to which we referred in the contract.
• Like Water for Chocolate, which was an excellent book, was made into a movie.
• Barcelona, which I visited last year, has a lot of interesting architecture.
• Posey’s Cafe, which Chester recommended, is a fantastic restaurant.
• Our ability to use language is one of the things that set us apart from animals.
• For camp the children need clothes that are washable.
• The 1964 Ford Mustang, which propelled Lee Iacocca to the top of the automobile industry, is now considered a classic.
• The child who is running around the room is my niece.
• I bumped into the child who was running around the room.
• The suspect in the lineup, who owns a red car, committed the crime.
• The book that I finished reading yesterday was really fascinating.
• I just finished reading a book that was fascinating.
• I finished reading Like Water for Chocolate, which was made into a movie.
• The city that I want to visit the most is Shanghai.
• Professor Shevchenko, who is my teacher, has been at this college for 25 years.
• Shanghai was the best city that I visited in all of Asia.
• For camp the children need sturdy shoes, which are expensive.
• The store honored the complaints that were less than 60 days old.
• My wife, whom I love dearly, is a brilliant physicist.
• The suspect in the lineup who has red hair committed the crime.
• The study was limited to US citizens who have never been to Canada.

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Source: https://academicguides.waldenu.edu/writingcenter/grammar/clauses