Colons are among the least understood punctuation marks, but they are common enough in formal writing that it is important for everyone to know how to use them properly. In this post, I provide a few simple tips to ensure that anyone can use colons properly.
Let's start by outlining the general pattern for colon use. After that, we'll talk about some exceptions.
What Comes Before A Colon?
In most cases, a colon must be preceded by a complete sentence. This is because a colon—like a period or a semicolon—signals the end of a complete thought. For this reason, the following examples are incorrect:
What I want to know: What is it like to be a famous actor? The truest statement I've ever read: "Imagination is more important than knowledge." His final request: Donate the proceeds to needy children. The new software's features include: instant payment, friend lists, and online chat.
The first two sentences are incomplete, as they do not have verbs. The third and fourth sentences do have verbs, but the colons are incorrect because "His final request" and "The new software's features include" are not complete sentences. The third sentence needs an additional verb before the colon to be correct; the fourth sentence would be correct if you just removed the colon, however.
In most cases, sentences such as these can be correctly written either with a colon or without one. Here are some correct versions of the example sentences, first with colons:
Here is what I want to know: What is it like to be a famous actor? This is the truest statement I've ever read: "Imagination is more important than knowledge." His final request was as follows: Donate the proceeds to needy children. These are some of the new software's features: instant payment, friend lists, and online chat.
In each case, the portion before the colon is now a complete sentence. Here are some correct versions without colons:
I want to know what it is like to be a famous actor. The truest statement I've ever read is, "Imagination is more important than knowledge." His final request was to donate the proceeds to needy children. The new software's features include instant payment, friend lists, and online chat.
For the first sentence, the question is not a direct quotation, so the most concise way of writing the sentence is to make the question implied instead of directly asking it. This involves rephrasing without the question mark (or the colon). The second and third sentences have added verbs to make them complete; for these sentences and the last one (which already had the necessary verb), I've omitted the colons because the sentences would be incomplete if they ended after the verbs.
What Comes After A Colon?
There are four main ways to follow a colon:
A list or single example
A complete statement that amplifies what came before the colon
Each of these is represented in one of the examples above. You can introduce any of these with a complete sentence followed by a colon; however, note that you can also introduce any of them without using a colon.
Lists: You need a colon before a list if the sentence starts with a phrase such as "This is" or "There are," or if the part before the list includes "as follows" or "the following." Such sentences will be complete before the colon. However, you do not use a colon if the list is preceded by a simple verb such as "is" or "include"; this is because a complete sentence cannot (usually) end with such a verb. Just put the list right after the verb, with no punctuation in between. Here is the same list written (correctly) in both ways:
Here are the three most popular artists at the festival: Lizzo, Billie Eilish, and Kanye West. The three most popular artists at the festival are Lizzo, Billie Eilish, and Kanye West.
Quotations: You need to precede a quotation with a colon only if the preceding sentence is complete; if the question is introduced with a word such as "said," "replied," "wrote," "asked," or "noted," then you use a comma instead of a colon, as the text preceding the quote will not be a complete thought. Here is the same quotation introduced (correctly) in both ways:
I spoke with authority drawn from my experiences: "Using violence is always harmful." With authority drawn from my experiences, I said, "Using violence is always harmful."
Questions: If a question is quoted, use the advice above; the following advice applies only to questions that are not quotations. When presenting a question, you will generally use a colon if the entire question is directly presented, followed by a question mark. If the question is only implied and is not presented in full, do not use a colon before it. Both these examples are correct:
The question never left my mind: How can I leave without attracting notice? The question of how I could leave without attracting notice never left my mind.
Amplifying Statements: This is the trickiest category because there is a lot of overlap between colon and semicolon use in this case, as both the part before the colon and the part after it must be complete thoughts. My advice is as follows:
If the two parts are not directly related, separate them with a period (two sentences).
If the second part enhances or expands upon the first part, separate them with a colon.
If the two parts are related in any other way (for instance, if they present a cause-and-effect relationship), separate them with a semicolon—or a comma and a conjunction.
Here are examples of how to correctly combine two complete statements:
The first astronauts on the moon brought an American flag. There was not enough room on the spacecraft to bring much else.
Only two of the three astronauts on that mission set foot on the moon: The pilot, Michael Collins, stayed in orbit.
Most people think Armstrong said "One small step for man..."; however, he actually said, "One small step for a man..."
In the first example, the two thoughts are not closely related, so a period is the best punctuation to separate them. In the second example, however, the second thought clearly enhances the first by explaining what the third astronaut was doing instead of walking on the moon. As a result, a colon is the best connecting punctuation. In the final example, the two thoughts are clearly related, but the second one does not expand upon the first (it forms a contrast instead), so a semicolon works best.
Note that, even when a colon is a correct way to connect two complete thoughts, it is not the only valid way to do so. A semicolon or a period will also work, though they may not be quite as effective. (Indeed, in the second example above, either a semicolon or a period would be fine.) Thus, if you are connecting two complete thoughts and are not sure which punctuation is best, I'd recommend using a semicolon or period to be safe. Colons are much more restricted in their use, so they are more likely to lead to errors.
Other Valid Uses Of Colons
Finally, let's go through a few less common ways of using colons.
To Introduce Speech In Dialogue: In plays, transcripts, and other forms of writing in which most of the text is dialogue, colons are used between the speaker's name and that person's dialogue.
Teacher: Do you know the multiplication tables? Long division? Bart: I know of them.
In Formal Greetings: When writing a formal message, put a colon after the greeting. (Use a comma instead if the message is more informal.)
Dear Hiring Manager: I would like to be considered for the sales associate position, as advertised on LinkedIn.
To Define Categories When Verbs Are Omitted: Sometimes, in informal writing, you want to define categories and examples simply, without using complete sentences. In these cases, you can list the category, followed by a colon, and then the examples.
Strengths: speed and accuracy. Weaknesses: cost and complexity
After Headings In Some Styles: Finally, colons are sometimes used to separate an inline heading from the following text (as in this paragraph). Note that this depends on the style; some style guides prefer periods after inline headings. In addition, headings that stand alone (on their own line) do not typically end with any punctuation.
That's all I have for today! I hope this guide to correct colon use has been helpful. Please let me know if you have any questions about colons or other punctuation by leaving a comment or sending me an email at firstname.lastname@example.org. And, as always, if you don't want to worry about correct colon use, I would love to edit your documents! Simply go to my main page for more information or to request a quote.