In my experience, the colon is one of the most frequently misused punctuation marks. For instance, it is often confused with the semicolon. This confusion, however, is somewhat justified because these two marks do have a point of overlap: both the semicolon and the colon can be used between two related independent clauses (i.e., clauses that can each stand alone as a complete sentence). If you’ve read my post on semicolons, you may remember that the rule of thumb for distinguishing between these two punctuation marks is that a semicolon separates two related clauses, while a colon is used when the second clause explains or elaborates on the first clause. Naturally, because both marks deal with clauses in a close relationship with each other, there are some cases where either mark will do. To avoid grammar mishaps in this grey area, most guides suggest using the colon sparingly; this is good news for those who struggle with grammar because the semicolon is less nuanced than the colon (after all, the semicolon only has two main uses). And, of course, another option is to separate the independent clauses into two sentences with a period between them.
Nevertheless, a colon is necessary in multiple other contexts to call attention to what follows it. These are the five grammatical uses of a colon:
As mentioned, a colon introduces a second independent clause that expands on or illustrates the preceding independent clause. To better navigate this grey area between colons and semicolons, remember that a colon is preferable when the second clause is not just parallel to the first but follows from it. Again, the difference is subtle, so it’s best to use a semicolon if you’re unsure.
He would never eat those granola bars: he’s allergic to nuts. → It’s preferable to use a colon because the second clause provides a reasoning for the first clause.
He would never eat those granola bars; he usually makes his own snacks at home to avoid any unsuspected allergens. → It’s preferable to use a semicolon because the clauses are related but their meanings are not totally intertwined.
A colon separates a title from a subtitle (like the title of this blog post). As in the first point, the clause after the colon (the subtitle) elaborates on the clause before the colon (the main title). However, in a title, neither the main title nor the subtitle need to be independent clauses, and of course, the words must be capitalized according to the style guide you’re following.
A colon introduces a list (like the one I’m presenting right now) or series, but only if the list follows an independent clause and does not separate the verb from its object(s). Not meeting these conditions is another common way that the colon is misused. Writers need to be aware that a colon is not required before every series or list; when the sentence is grammatically correct without it, toss out the colon.
Introducing a List
Connie baked three pies for Thanksgiving dinner: pumpkin, apple, and pecan. → RIGHT: the colon is preceded by an independent clause.
Connie likes to bake: pumpkin, apple, and pecan pies. → WRONG: the colon separates the verb (“to bake”) from its object (“pies”).
Introducing a Series
Levi pondered three equally appealing ideas for spending the next hour: He could watch the latest episode of his favourite television series. He could cook a tantalizing meal to eat as leftovers for lunch tomorrow. Or he could take a nap. → RIGHT
Levi pondered three equally appealing ideas for spending the next hour: he could watch the latest episode of his favourite television series, cook a tantalizing meal to eat as leftovers for lunch tomorrow, or take a nap. → also RIGHT
A colon introduces a quotation or a question when the colon follows a complete sentence. This usage is common before a block quotation (a lengthy quotation that is set off from the surrounding text).
Introducing a Quotation → L. M. Montgomery begins Anne of Green Gables with an introduction to Avonlea’s most notorious busybody: “Mrs. Rachel Lynde lived just where the Avonlea main road dipped down into a little hollow . . . if she noticed anything odd or out of place she would never rest until she had ferreted out the whys and wherefores thereof.”
Introducing a Question → Garrett pondered the meaning of this outburst: Where did he go wrong?
A colon follows the greeting in a formal letter (e.g., a cover letter); for example,
Dear Sir:
Dear Hiring Manager:
To Whom It May Concern:
Beyond its grammatical uses, a colon is used in various technical contexts as well. For example, it’s used between chapter numbers and verse numbers in sacred texts (e.g., Genesis 50:20) and between numerals in a ratio (e.g., 2:1). Note that a space is not inserted after the colon in these cases.
Finally, a glaring point of confusion for many writers is whether or not the first word of an independent clause following a colon should be capitalized as if it were the beginning of a new sentence. After all, the first word is never capitalized after a semicolon (unless it’s a proper noun). Thankfully, there are only two instances in which the first word after a colon is capitalized: when the colon introduces a series of related sentences and when it introduces a quotation or question.
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