Commas, Semicolons, and Colons

Commas

Commas are the most frequently used--and misused--punctuation mark.  It is not always correct to have a comma simply because you have paused.  There is no "word-to-comma" ratio.  You can have a lengthy sentence with no commas required or a short sentence with several.  The point is to recognize the elements that your sentences are composed of and to know the rules for using--or omitting--commas in them.

Commas are needed in the following instances:

In front of a coordinating conjunction used to join independent clauses

Tolstoy's War and Peace is long, but Joyce's Ullyses is even longer.

Online courses are hard, so students who enroll in them must manage their time well.

I went to New York last summer, and I had a great time.

Following introductory phrases and dependent clauses

Without realizing it, I bought the same book online twice.

When I shop online, I really need to be careful.

To separate three or more items in a series

We found a vacation spot that was sunny, beautiful, and inexpensive.

I love pizza, lasagna, and eggplant parmesan.

Chemistry, math, and physics were my hardest classes.

  • You may have had teachers in elementary school or high school tell you that you don't need the comma in front of "and" because it replaces the comma. That isn't really logical because conjunctions connect and commas separate. Also, sometimes elements have conjunctions in them as part of their name.  The comma before the first "and" in the sentence below helps to make clear that the last item, "Arts and Entertainment," is just a single item in the series.

My favorite television channels are PBS, the History Channel, and Arts and Entertainment.

To separate items that are the alike (the same parts of speech) with commas

Nouns and noun phrases:

We drove through Bakersfield, Portland, and Seattle.

We watched Freeway, Pretty Woman, Ever After, and The Company of Wolves.

Adjectives:

We saw a funny, exciting, original movie last night. 

Adverbs:

I am deeply, truly sorry.

With nonrestrictive elements (elements that can be taken out of sentence without changing the meaning of the sentence)--note how the nonrestrictive elements below (indicated in purple) can be removed without altering the meaning of what is left behind.

James Joyce, who wrote Ullyses, is one of the pioneers of literary modernism.  (James Joyce is one of the pioneers of literary modernism.)

I read Joyce's A Portrait of the Artist as a Young Man, which is a much more accessible work. (I read Joyce's A Portrait of the Artist as a Young Man.)

Feeling quite nervous, I opened the letter from credit card company. (I opened the letter from credit card company.)

I love to travel.  For example, I went to New York last summer.  (I went to New York last summer.)

Unfortunately, I didn't get to see Central park.

My boyfriend, however, did get to see the park.

With personal titles, addresses, and dates

He read an article by John Smith, Ph.d.

Send the application to John Smith, 1801 Panorama Drive, Bakersfield, CA 923305.

She graduated on May 12, 2006.

In front of quotations preceded by introductory words, such as "said," "asserts," "writes," and "claims"

Randal Marlin states, "British propaganda in WWI was very extensive, effective, and well documented."

Commas should not be used in the following instances:

After an independent clause and before a coordinating conjunction followed by a phrase

I went to New York last summer and had a great time.

I went to the Louvres and saw the Mona Lisa.

Between subjects and verbs

Many varieties of birds fly south for the winter.  ("Fly" is the verb, and the phrase that precedes it is the sentence's subject.)

Before or after a series (unless the whole series is nonrestrictive)

Last night I watched reruns of Buffy the Vampire Slayer, Angel, and Alias.

After coordinating conjunctions

I went to the play, but I soon got bored.

After "such as" or like"

He was told to avoid consuming anything that might aggravate his blood pressure, such as caffeine or salt.

Between independent clauses that are not connected by a coordinating conjunction

She read a book called The Lovely Bones.  She really liked it.  (Use of a comma would be an error called a "comma splice.")

With a question mark or an exclamation point

We read Do Androids Dream of Electric Sheep? and then we wrote an essay about it.

Semicolons

A semicolon looks like a comma with a period floating above it.  It is stronger than the comma, but not as strong as the period--it does not terminate a sentence.  The semicolon is not interchangeable with the colon, so be careful not to confuse them.  The semicolon has only two uses.

Semicolons are needed in the following instances:

Connecting closely-related independent clauses that are not joined by a coordinating conjunction

We saw the movie Syriana last week; we liked it.

I went to New York last summer; however, I didn't get to see Central Park.

Jane Yolen is a prolific writer; she has published over a hundred books, article, and short stories.

  • Basically, for this use, remember that you should only use a semicolon if a period would also work.

Separating items in a series when the items themselves have commas

Last month I read Wicked, which tells the story of the Oz characters from the witch's point of view; Wide Sargasso Sea, which tells events of Jane Eyre from the mad wife's point of view; and Grendel, which tells the story of Beowulf from the monster's point of view. 

Last month I read Wicked, which tells the story of the Oz characters from the witch's point of view; Wide Sargasso Sea, which tells events of Jane Eyre from the mad wife's point of view; and Grendel, which tells the story of Beowulf from the monster's point of view. 

  • The three items are Wicked, Wide Sargasso Sea, and Grendel, and each novel is followed by nonrestrictive information joined to the novel it describes with a comma.

Colons

Colons have only one use within sentences: to introduce sentence elements after independent clauses.  They have other uses outside sentences, but in the bodies of your essays and papers, remember that you should only use them when introducing a sentence element (like a series) after something that could, grammatically, stand alone as a sentence. 

Be careful with colons--you have undoubtedly seen them misused numerous times.  A lot of writers, including professionals who know better, use them whenever they introduce a sentence elements.

Colons are needed in the following instances:

Introducing sentence elements after independent clauses

I went to the library, and I checked out three books: Wicked, Wide Sargasso Sea, and Grendel.

I checked out the following books: Wicked, Wide Sargasso Sea, and Grendel.

Setting off subtitles

Trust Us We're Experts: How Industry Manipulates Science and Gambles with Your Future is a book by John Stauber and Sheldon Rampton.

Examples of types of common colon mistakes:

I checked out: Wicked, Wide Sargasso Sea, and Grendel.  ("I checked out" is not an independent clause.)

I checked out some books, including: Wicked, Wide Sargasso Sea, and Grendel.  ("I checked out some books, including" is not an independent clause.)