Punctuation marks are the signposts of prose. They indicate what’s important and where to pause. They add rhythm to your sentences. They help your readers follow the twists and turns of your thoughts.

But there are so many different kinds of punctuation marks that it can be tricky to decide which one to choose. Periods and commas are the most common, but trying to write with only these two at your disposal would be like trying to build a whole house with only one size of nail and one size of screw: it would make for quite a boring structure, that is! Colons, semicolons, and dashes are less common—on the second tray in your writer’s toolbox, perhaps—but every bit as important to producing clear, elegant writing. Here are some tips about how (and how not) to use them.

Semicolons

Semicolons are used to join two independent clauses, creating a compound sentence.

Example: The building was very quiet; most of the staff had left for the night.

Here, “The building was very quiet” and “Most of the staff had left for the night” could each stand as sentences alone (they each have a subject and a verb), but the semicolon, as opposed to a period, indicates their close relationship—in this case, it hints at a relationship of causality (“The building was very quiet because most of the staff had left for the night”).

A semicolon can be used instead of a period, then, and it can also be used instead of a conjunction.

Example: The building was very quiet [;]/[but] several staff members continued working on the seventh floor.

A common problem occurs, however, when writers double up on semicolons and conjunctions—as would be the case if the example above had used both a semi-colon and “but.” This is not strictly incorrect, since independent clauses (and full sentences) can begin with conjunctions, but it should be done only sparingly, for effect. It indicates a dramatic pause in the middle of the sentence, which can sometimes be a strong rhetorical move.

Writers also frequently use a comma instead of a semicolon before conjunctive adverbs such as “however” and “therefore” when these are found at the beginning of a new independent clause. This is an error: joining independent clauses with only a comma makes a run-on sentence.

Example: He wanted to drive to the cottage, however, the car was quite unreliable.

Here, the first comma should be a semicolon. It is a particularly tricky case, because you can also have sentences such as, “He wanted to drive to the cottage, however, because it would be faster than taking the bus.” In this second case, though, the second part (“because it would be faster than taking the bus”) is not an independent clause, and so a semicolon would be too strong to divide the sentence.

A handy trick for remembering the role of a semicolon in a sentence is to picture it: it is stronger than a comma (its bottom half) and weaker than a period (its top half). Semicolons deployed thoughtfully and strategically will add flow and nuance to your prose.

Colons

Colons introduce ideas or examples that illustrate or amplify what has come before them. Like semicolons, colons can be used between two independent clauses, but only when the second clause illustrates or amplifies (or summarizes, explains, deepens, clarifies) the first one. Whereas the semicolon is a mark that breaks or indicates a pause, the colon is a mark that connects: think of it like a springboard into the next part of the sentence.

Example: Life is like a box of chocolates: you never know what you’re going to get.

This sentence contains two independent clauses, but they are very closely related, and the second clarifies the first. On the whole, colons are underused in this capacity—keep them in mind the next time you need to elaborate on something!

Colons are often overused, however, in introducing lists and examples.

Example: I like many different kinds of ice cream, including: mint chocolate chip, butterscotch ripple, cherry cheesecake, chocolate peanut butter, and pistachio.

Here, “including” introduces the list, so a colon is redundant—“including” operates as the springboard. Moreover, writing “including” before the colon means the first clause is not independent. The simplest solution is, of course, to remove the colon.

You could also write: I like many different kinds of ice cream: mint chocolate chip, butterscotch ripple, cherry cheesecake, chocolate peanut butter, and pistachio.

Just remember, to introduce a list with a colon the introduction part of the sentence needs to be an independent clause. “I like many different kinds of ice cream” is a full sentence; if you tack “including” onto the end of it, it isn’t.

For additional punctuation tips, read “4 Handy Tips: A Punctuation Primer.”

Dashes

Like colons, dashes often operate as springboards (they even look like springboards) leading you into an example or clarification. Sometimes dashes and colons can be used more or less interchangeably (although individual writers and editors might have their own strong opinions about which is correct). But whereas colons unambiguously indicate that elaboration or further definition is ahead, dashes are more informal and are above all used for emphasis.

Example: I like to run for half an hour every morning—no more, no less.

Here, the dash introduces a clarification. “No more, no less” is neither an independent clause nor a list, and so it does not need to be introduced by a colon. Instead, it is tacked on to the sentence as a kind of afterthought—an informal elaboration.

Dashes are often used to enclose or set apart material in the middle of a sentence. This might be anything from a few descriptive details to an independent clause.

Example: The contents of the room—the old armchair, the framed photographs, the stacks of books—reminded her forcefully of her grandmother.

Example: My new roommate—she was from Winnipeg—was instantly likeable.

Frequently in these cases it would also be acceptable to use parentheses. Parentheses tend to downplay the significance of an aside, whereas dashes can emphasize or highlight it; parentheses bury, while dashes elevate.

Dashes are rarely grammatically necessary; they can almost always be replaced with a colon, parentheses, or commas. But they are very useful for adding splashes of detail or colour to your writing: remember—here’s a helpful trick—“a dash of this, a dash of that.” Just be careful not to overuse dashes in the middle of your sentences: this can make them long, choppy, and difficult to follow.

With all of these essential punctuation marks in your writer’s toolbox, constructing complex and structurally sound prose will be a piece of cake!

Want a monthly editing tip? Sign up for our monthly newsletter and have 
helpful editing tips delivered directly to your inbox.