Punctuation Rules

The Colon

A colon (:) appears at the end of a main clause and introduces a list, a restatement, or an elaboration of the main clause. It is also used to introduce extended quotations.

Examples

3a. A colon appears at the end of a main clause. Because of this rule, you can ask yourself this question: "Considering the wording before this point, could I put a period or question mark here?" If the answer is yes, then you may use a colon to attach the following material to the sentence as long as that material is a list, a restatement, or an elaboration.

This rule also means that you should not use a colon to introduce a list which completes the kernel of a main clause.

wrong: On our farm, we grow: wheat, alfalfa, and soybeans.
okay: On our farm we grow three crops: wheat, alfalfa, and soybeans.
3b. A colon introduces a list. It is important to remember that a colon introduces a list only when the list is attached to a completed main clause.
We sent copies to our regional offices: the north-central office in Traverse City, the south-east office in Tampa, and the south-west office in Santa Fe.

Unable to ascertain the exact cause of death, the doctor turned the body over to a team of forensic experts: Janice Trico, the county coroner; Gerald Sota, the county sheriff; and Michael Jesperson, the head of the county crime lab.

 3c. A colon introduces a restatement of the main clause.
No matter how often she turned it over in her mind, Carol couldn't decide who was to blame: She couldn't decide whether to blame herself or Jim.
Notice that the second main clause says the same basic thing as the first. It is often hard to distinguish between a restantement and an elaboration because any time you say something a little differently, you tend to add new information; that is, you elaborate a little. Also notice that the second main clause is capitalized. Different style guides recommend different practices: Some suggest a capital; others suggest lower case. Check the handbook you are using in class, or ask your teacher for her or his preference. Try to be consistent.

3d. A colon introduces an elaboration of the main clause.

Different style guides recommend different practices: Some suggest a capital; others suggest lower case.

I've decided not to take the assistantship for next year: The Prudential company has made me an offer I can't turn down.

3e. A colon introduces a long quote, which is often indented.
Jeremy Rifkin has argued that Darwin built his theory on the analogy between economics and nature:
It was Darwin who was ultimately responsible for formalizing the analogy between economics and biology; and in so doing, says sociologist Robert Young, he gave "the mark of scientific respectability to the equation of the division of labor with the laws of life." Algeny, page 87.