No, this is not about the medical procedure. Let’s take a look at colons of a punctuational kind.

The colon is a strong mark. Colons don’t get lost at the end of a word the way commas often do. However, unlike, say, semicolons, they don’t inspire great passion. I have a T-shirt that praises semicolons. I once gave a writer friend a semicolon sticker and she promptly drew a red international NO symbol over it. That’s what I mean: writers and editors tend to have strong feelings about semicolons, pro and con. Colons not so much, and so far I haven’t come across a T-shirt that expressed an opinion about colons.

When it comes to numbers, the colon is a workhorse, getting the job done without fanfare. We use them with time (it’s now 9:44 a.m. where I am; in 24-hour military time, however, that would be a non-colonic 0944). We use it to separate chapter and verse in the Bible and certain other books (Psalm 23:6). We use it to express ratios (3:1 means three parts of one thing to every one part of another).

The colon comes in handy in number-free text too. Off the top of my head, here are some conventional uses for colons: to separate title from subtitle in bibliographies and endnotes; to separate speaker from speech in scripts, interview transcriptions, and other dialogue; and to introduce lists (see how I snuck that one in at the beginning of this sentence?).

With lists, what precedes the colon should almost always be a complete sentence. If it isn’t, you may not need any punctuation at all. Colons are often found in the wild where they aren’t needed, as in “For our expedition, you’ll need: comfortable shoes, insect repellent, and a water bottle.” Either lose the colon or add “the following” or something similar before it.

The colon can be used with speech that doesn’t follow the script or interview style of alternating speakers. This came up in an online editors’ group the other day. A copyeditor had an author who was a little colon-happy with dialogue like this:

She said: “I won’t be home till after dark.”

Virtually everyone who responded preferred a comma in such situations. Why? Well, the simple explanation is that the most common style guides used in British and American English say so (see, for instance, the Chicago Manual of Style, the Associated Press Stylebook, or Hart’s Rules), but I’m interested in why they say so, and why in this case I agree with them. So here are a couple of reasons:

• Colons are often used to introduce formal and/or lengthy speech. This snippet of dialogue is neither formal nor lengthy.
• As noted above, colons are strong. You notice them. They may lead you to expect, consciously or not, that something momentous is coming. Commas are unobtrusive, and in dialogue that’s usually a good thing.

With formal and/or lengthy speech or quotations, a colon is fine.

Colons can also be used in dialogue that doesn’t include a tag attributing it to a specific speaker, as here:

Melina was adamant: “We are not leaving until tomorrow.”

No tag is needed here: It’s clear that Melina said “We are not leaving until tomorrow.” What follows a colon often explains or elaborates on what precedes it. Often the colon is one of several options, and the one you choose will subtly influence how your sentence is read. Here’s an example I came up with several years ago, which I keep trotting out because I’m too lazy to come up with another one:

1. I’m an editor and writer. Without functioning eyes, I can’t work.
2. I’m an editor and writer: without functioning eyes, I can’t work.
3. I’m an editor and writer — without functioning eyes, I can’t work.
4. I’m an editor and writer; without functioning eyes, I can’t work.

All four sentences are perfectly correct, but to the careful writer and the attentive reader they aren’t identical. Example 2, the one with the colon, sets up a cause-and-effect relationship between the first statement and the second. It could be replaced with “therefore” or “so.” Example 3, with the em dash, does that to some extent, but the visual space between the sentence’s two parts loosens the connection between them. (If you’re interested in a more extensive discussion of the four examples, check out “Praisesong for the Semicolon,” my 2014 blog post about, you guessed it, semicolons.)

The author of my current copyedit loves em dashes. I’m letting him have plenty of them, but where the cause-and-effect relationship is especially strong between the first part of the sentence and the second, or when what follows the colon clearly explains what precedes it, I’m suggesting colons.

One last thing about colons: Example 2 above illustrates a popular convention in U.S. English: a single full sentence following a colon doesn’t start with a capital letter. (The sentence I just typed does too. I’ve probably used more colons in this blog post than in anything else I’ve written in the last year.) This is a style thing, and one that one of my major U.S. trade publisher clients parenthetically but pointedly “does not endorse.” These days I tend to follow the author’s lead, because nearly all the authors I deal with are pretty good writers and because if I’m not busily changing caps to lowercase I’m more likely to notice other things that could use my attention. Just about everyone agrees, however, that when a colon is followed by more than one related full sentence, they all get initial-capped.

Any questions or comments about colons? or anything else?