Column: A Word, Please: When to use a colon: a user’s guide

I’ve talked about colons more than once in this column, but my focus is usually limited in scope. I zoom in on the little questions, like how many spaces to put after a colon and whether it should be followed by a capital letter or lowercase.

That is, I talk about how to use colons, but I’ve never spent much time on when or why to use colons. I guess I figured people already know how.

Big mistake.

It turns out, the No. 10 most researched question on the Grammar Girl website is “How to use colons.”

One might surmise I’ve been derelict in my duties. So without further ado, here’s what you’ve been missing: a comprehensive look at colons.

The colon has a couple of different jobs, all of which can be explained in these broad terms: A colon introduces something. Sometimes, the idea is just to tell the reader, “Here you go. Here’s that thing or things I wanted to tell you about.”

This colon, according to the Chicago Manual of Style, “should generally convey a sense of ‘as follows.’”

The sandwich comes with your choice cheese: Swiss, American or provolone.

In this example, the stuff after the colon is a list.

But you could also put an independent clause, which is essentially a complete sentence, after a colon: This sentence is a case in point. Or you could place after the colon a sentence fragment or phrase: a less-common scenario.

When it’s between two complete clauses, a colon is working in a manner very similar to a semicolon; both can join independent clauses in a single sentence.

The difference is subtle-bordering-on-indistinguishable, but I would term it this way: The semicolon shows that the two clauses are closely linked; they deal with the same thing. The colon, however, uses the first clause to introduce the second.

They’re not quite peers. The first clause is more like the opening act for the one that comes after the colon.

That brings us to our next job for the colon: to amplify a message. “I want you to know this: You will always be welcome here.”

If you don’t see much difference between the job of amplifying information and the job of simply introducing it, that’s because there isn’t much difference.

Colons can also be used to introduce a quotation. Mary said: “Pick up a quart of milk.” That’s most often a job for a comma, but quotations, especially longer ones, can be introduced with a colon as well.

Even speech that isn’t in quote marks can be introduced with a colon. This is especially true when it’s formatted as dialogue. Here’s an example from the Chicago Manual.

Michael: The incident has already been reported.

Timothy: Then, sir, all is lost!

And, of course, you can use a colon in a direct address, meaning after someone’s name in a correspondence like “Dear Sirs” or “Ladies and Gentlemen.” If you prefer a comma after one of those, that’s an option, too.

All editing styles agree that you need just one space after a colon, regardless of what type of information follows. But they don’t agree on when to capitalize.

According to the Associated Press Stylebook, you capitalize the first letter after a colon when it begins a complete sentence. Otherwise, use lowercase. Chicago, though, says to capitalize the first letter after a colon only if two or more sentences follow.

Even though they’re easy to use, colons get misused quite a bit, too. A common mistake is to use one after the word “including.” A colon is unnecessary there, since its meaning is pretty much implicit in “include.”

And don’t use a colon to introduce objects of a verb. “Bruce likes apples, oranges and pears” should not have a colon after “likes.”

As Chicago puts it, “If a colon intervenes in what would otherwise constitute a grammatical sentence … it is probably being used inappropriately.”

JUNE CASAGRANDE is the author of “The Joy of Syntax: A Simple Guide to All the Grammar You Know You Should Know.”