7 Golden Rules for Colon Usage

The colon (:) is one of the more mysterious English punctuation marks because its usage has varied historically. Its origins date back to Ancient Greece and Roman times, when it was introduced for marking speech pauses longer than commas and shorter than full stops.

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However, not until the invention of the printing press, during the Renaissance, did the colon's modern-day usage become more established. The clear-cut rules for colon usage are much more standardized today, but their subtleties can sometimes generate confusion about why and when to include them in articles and books.

The primary purpose of the colon is to introduce things. It signals a pause used to connect clauses with a direct relationship, like a forward arrow showing something to follow. Colons are also sometimes used with numbers for non-grammatical purposes. These are seven of the most important rules for using commas in your articles, books, letters, and other content forms.

An important function of the colon is to introduce lists. It can introduce lists within sentences, as a series, or more separate bullet-pointed alternatives. Here are some examples of colon usage for introducing lists:

However, you should only add colons for introducing lists after independent clauses that can stand alone as sentences. If a preceding introduction is not complete, do not add a comma before the list. These are some examples of incorrect (unnecessary) colon usage for lists with incomplete introductions:

You can add colons for introducing quotations. Again, however, you should only do so when a full independent clause introduces the quote. For example, one notable passage from Sun Tzu's Chinese military treatise says this: "Know thyself, know thy enemy. A thousand battles, a thousand victories."

Some confusion can arise from when to introduce quotes with colons or commas. The Associated Press recommends introducing shorter, one-sentence quotes with commas rather than colons. If you introduce a quote with an incomplete clause, add a comma before it rather than a colon.

As colons highlight a direct relationship, you can use them for introducing explanations or questions. Including colons for explanations or questions adds more emphasis to what follows them. The one thing to remember is that an independent clause must precede the explanation or question added after the colon. Here are some examples of colons introducing explanations and questions:

Many articles, books, video games, and movies include colons in their titles. If you want to incorporate a subtitle within an article or book title, you must add a colon to separate them. Films like "The Lord of the Rings: The Fellowship of the Ring," "Spider-Man: Homecoming," and "The Smurfs: The Lost Village" typically include colons for combining series titles with more unique movie names. This trend for including colons in titles is also popular within the video game industry.

A salutation is an introductory greeting added to the beginning of a letter. You should add colons to salutations in more formal business letters. That is preferable because a colon adds greater formality to a salutation than a comma, as in these examples:

Freelance writers sometimes need to refer to ratios in their articles and books for comparing quantities. Mathematical ratios always include colons to separate their numbers. For example, 2:1 is a ratio with a colon separating its units.

However, it's not necessarily a strict rule to include colons for ratios when you can spell them out like two to one. It is more a mathematical rule to include colons for ratios than an English one.

You should include colons for digital time, much the same as alarm clocks do. For example, 14:30 is the digital time for the 2:30 p.m. 12-hour alternative. However, it's also standard practice to include colons in 12-hour time format combined with a.m. (before noon) and p.m. (after noon).

The semicolon (;) is a different punctuation mark that can sometimes get confused with the colon. Many of the colon's functions don't overlap with the semicolon. However, both show pauses and can be used for connecting related clauses in the same sentences.

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The key difference to remember is that a semicolon must always connect two full independent clauses. Its primary purpose is to connect two independent clauses, which could be separate sentences, that aren't joined by the conjunctions and, but, or, for, nor, and so. Here are some examples of semicolon usage:

Semicolons are included to connect related independent clauses in the examples above. It wouldn't necessarily be wrong to replace the semicolon with a colon for some of those examples. However, colons are more suitable for introducing second clauses that provide clearer clarifications or explanations for the previous ones. In contrast, semicolons merely join related independent clauses without and, but, not, or, for, and nor coordinate conjunctions.

The overall functions of the colon are relatively straightforward, but it's easy to appreciate why it can be confusing when introducing quotes, lists, and explanations. Try not to get them mixed up with semicolons, and remember that full independent clauses must precede colons when used for quotations, lists, explanations, and questions. It's important to include colons in your articles or other content forms because they add clarity and structure by introducing lists, emphasizing explanations or questions, and presenting quotations.