Punctuation Series: Colons | Commas | Dashes | Semicolons
The primary grammatical function of the colon is to introduce, emphasize or clarify a preceding thought or idea. Author Lynne Truss puts it this way in her book "Eats, Shoots & Leaves" (2004):
A colon is nearly always preceded by a complete sentence, and in its simplest usage it rather theatrically announces what is to come. Like a well-trained magician’s assistant, it pauses slightly to give you time to get a bit worried, and then efficiently whisks away the cloth and reveals the trick complete.
Her description captures one of the most important rules of the colon: the clause preceding the colon is almost always a complete sentence.
Examples are the best way to illustrate:
- I only need two things to get off to a good start in the morning: a hot cup of coffee and a warm piece of toast.
- My gaze turned to the the last item on my bucket list: an Amazon expedition.
- John’s arms flailed in the water: he was drowning.
- There could be only one answer as to what happened: the witness had been murdered.
- I was so hungry I ate everything in sight: soda, eggs, chocolate bars and two bags of tortilla chips.
Like other types of punctuation, usage of the colon often comes down to stylistic license.
Take the following example:
I only need two things in the morning: a hot cup of coffee and a warm piece of toast.
The sentence can be rewritten without a colon:
The only two things I need in the morning are a hot cup of coffee and a warm piece of toast.
Alternatively, the colon could be swapped for the less formal em dash:
I only need two things in the morning—a hot cup of coffee and a warm piece of toast.
Many sentences that use a colon can be seen containing implicit questions that need answering. While the clause preceding the colon presents a standalone sentence from a grammatical standpoint, from an informational standpoint, the preceding clause is incomplete.
To illustrate, let’s look at a couple of sentences that are begging for colons:
- Laurel heard the voice of the one thing in the world that made her heart stop.
- The little girl clutched her favorite thing in the whole world.
- There were two things Fred hated on pizza.
The examples are complete sentences, but I want to know more when I read them. Here are the completed versions of the sentences using colons:
- Laurel heard the voice of the one thing in the world that made her heart stop: her mother-in-law.
- The little girl clutched her favorite thing in the whole world: her raggedy pink teddy bear.
- There were two things Fred hated on pizza: pineapple and anchovies.
I often find that I’m using the colon correctly when I am able to ask a “what” or “why” question about the first clause that is answered by the second clause. Not to belabor this point, but here are the questions I ask to make sure my colon is working properly:
- Who made Laurel's heart stop?
- What was the girl clutching?
- What does Fred hate?
In all three cases, the answer is given in the clause that follows the colon. Go back to other examples in this article and see if you can ask similar questions when you spot a colon. The formula is simple: the initial clause suggests something and the subsequent clause answers it.
Other ways to use the colon.
I’ve spent the bulk of this post focused on what I consider the primary grammatical use of the colon. However, the colon is in a number of other ways.
Here are a few of them:
- Introducing a quotation (in particular, for long quotations).
- Book titles or article headlines. For example, “Sapiens: A Brief History of Humankind.”
- Bulleted lists and outlines. I’ve included a number of examples throughout the article above.
- Written salutations. For example, “Dear John:”
- Dialogue in stage or screenplays. E.g. “Policeman: You’re under arrest!”
- In URLs. For example, https://www.google.com
- Time. For example, 10:30 pm.
- Ratios. For example, 5:1.
- Biblical references. For example, Genesis 1:4
- Certain bibliographic or citation formats.
As always, practice makes perfect. Find good examples, study them, and then create new sentences with colons. This is a great way to gain proficiency and confidence with English punctuation.
Lastly, here are a few further resources that I found useful:
- The Colon (aalto.fi): Finnish Virtual University website is straight-forward and mercifully ad-free (something difficult to find on English-centric grammar websites).
- Eats, Shoots & Leaves (lynnetruss.com): Fantastic book on English punctuation. The chapter titled “Airs and Graces,” discusses the colon—alongside the semicolon—in greater detail.
- Using Colons and Semicolons (colonsemicolon.com): A website dedicated to the two most feared punctuation marks in English.