The Use of Commas in Written English

Like all punctuation marks, commas ensure the clarity of writing by organizing similar elements and representing intonation present in spoken language. Commas perform ten basic functions.

1. Use commas to separate items in a series. Place a comma after each item in the series except for the last item. Place the last comma before the coordinating conjunction. For example:

• Dogs, cats, mice, and squirrels are mammals.
• Farmers grow yellow corn, orange pumpkins, green peppers, and purple grapes.
• The movie is long, dull, and overrated.
• Performers sing, dance, or act.

Do not use commas to separate subjects or objects with only two nouns or noun phrases. Do not use commas to separate predicate adjectives with only two adjectives or adjective phrases. Do not use commas to separate predicates with only two verbs or verb phrases. (The asterisk * marks incorrect usage.) For example:

• *Doctors, and veterinarians have medical degrees.
• *Cats like mice, and fish.
• *Snow is cold, and wet.
• *Athletes run, and jump.

2. Use commas to separate two or more independent clauses joined by coordinating conjunctions. The coordinating conjunctions are and, but, for, nor, or, so, and yet. Independent clauses contain both a subject and a verb that function as a complete sentence. For example:

• The baby ate his formula, and the toddler drank her milk.
• My brother wanted pumpkin pie, but my sister wanted chocolate cake.
• The student was confused, so the teacher offered extra help.
• I came, I saw, and I conquered.

3. Use commas between coordinate adjectives. Coordinate adjectives directly and equally modify or describe the same noun. The word order of coordinate adjectives can be changed without changing the meaning. For example:

• The restaurant served plain, tasteless soup. (plain and tasteless both describe the soup)
• The mean, malicious child kicked the puppy. (mean and malicious both describe the child)

Do not use commas to separate cumulative adjectives. The meaning of cumulative adjectives is dependent on the order of the adjectives. For example:

• The big blue house is on the corner. (big describes the blue house)
• The pretty calico cat likes to cuddle. (pretty describes the calico cat)

4. Use commas to separate nonrestrictive modifiers. Nonrestrictive modifiers are optional, meaning such modifiers can be added or deleted without changing the meaning of the main clause. For example:

• The book, which I left in my car, is from the library.
• The puppy, with the blue leash, belongs to me.

Do not use commas to separate restrictive modifiers. Restrictive modifiers are essential to the meaning of the main clause. For example:

• The book that I left in my car is from the library.
• The puppy with the blue leash belongs to me.

Nonrestrictive modifiers are distinguished from restrictive modifiers by the context of the sentence. The difference between the modifier with the blue leash in the first example and the second example is that the puppy in the second example can only be identified by the fact that he is wearing a blue leash, making the modifier necessary and restrictive. The inclusion of the modifier with the blue leash in the first example, however, is optional, additional information, and, therefore, nonrestrictive.

5. Use commas to separate appositives that are not essential to the meaning of the sentence. Appositives are nouns, pronouns, or noun phrases that modify or explain another noun, pronoun, or noun phrase. For example:

• John Lennon, the musician, was killed by a fan.
• An aspiring actress, my cousin always auditions for lead roles.

Do not use commas with an appositive essential to the meaning of the sentence. For example:

• My dog Espen is a shih tzu.
• The singer Stevie Nicks was a member of Fleetwood Mac.

On the next page we cover the other five functions for commas.