Last week I started a short punctuation series on semicolons, colons, and dashes. I had said it was going to be a two-part series, but I was only kidding myself. Once a person starts talking about colons and dashes, it's hard to stop. So we find ourselves not at the end of a two-part series, but spang in the middle of a three-part series: colons today, dashes next week.
By way of review, the semicolon is not a very flexible punctuation mark (though I have lots of students who find very creative uses for the semicolon). A semicolon can be used to separate items in a complex series (that is, lists in which one or more items includes a comma) or it can be used to join two independent clauses into a compound sentence. That's it: any other use of the semicolon constitutes a punctuation error.
Colons and dashes, on the other hand, are both a little more flexible than semicolons. For the purposes of this letter, I am going to stick to the uses of the colon within prose sentences and skip the many specialized uses in business memos, titles, bibliographical citations, scriptural citations, etc.
In preparing for this letter, I ran across a summary of the colon that I found very helpful: a colon signifies expectation or addition. In every proper use of the colon, you are adding something to a sentence that is already (grammatically) complete without it. The colon, then, either sets up an expectation that is fulfilled by the information after the colon, or it signals that you are about to give the reader bonus information that will add to his or her understanding of what you just said.
The prose uses of the colon can be boiled down to five:
1. Use a colon to introduce a list. That's what the colon in the previous line is doing. It is introducing a list of five uses of the colon. However, there is a big caveat: the colon is appropriate ONLY if it is preceded by an independent clause (aka a complete sentence). If the list serves an integral grammatical function in the sentence, DON'T insert a colon. Consider these three sentences:
Sentence 1. The ingredients of chocolate cake include flour, sugar, butter, eggs, and cocoa powder.
Sentence 2. Mom made my birthday cake from flour, sugar, butter, eggs, and cocoa powder.
Sentence 3. Mom sent me to the grocery store to pick up the ingredients for my own birthday cake: flour, sugar, butter, eggs, and cocoa powder.
Each of these three sentences includes a list of five ingredients. Why, then, does a colon introduce the list in Sentence 3, but not in Sentences 1 or 2? In Sentence 1, the list serves as the direct object for the verb include. In Sentence 2, the list serves as the object of the preposition from. Since you wouldn't put a colon between any other verb and direct object or between any other preposition and object of preposition, you wouldn't put one here.
In Sentence 3, on the other hand, the list is tagged onto a sentence that is already complete and self-contained. The colon sets the expectation for additional information beyond the grammatically complete idea that precedes it.
The key idea here is grammatical completeness. Consider this sentence:
Here are the five main ingredients of a chocolate cake: flour, sugar, butter, eggs, and cocoa powder.
In an important sense the sentence before the colon is an incomplete idea; the list isn't bonus information, but the whole point of the sentence. Nevertheless, the colon is appropriate because the sentence preceding it is grammaticallycomplete.
2. Use a colon to introduce certain appositives at the end of otherwise complete sentences. An appositive is a noun or noun phrase that renames another noun that is adjacent to it (usually the appositive comes immediately after the noun it renames, but occasionally it comes immediately before). In most cases, an appositive is set off from the noun it renames by nothing more interesting than a comma, and often not even that. Consider these three sentences, each of which has an appositive in bold:
Sentence 1. When my cousin Fernando pulled out his accordion, everybody left the karaoke bar.
Sentence 2. My dog loves to chase the mailman, a skinny fellow with a handlebar mustache.
Sentence 3. My dog has a favorite hobby: chasing the mailman.
If you're wondering why a skinny fellow with a handlebar mustache gets commas but Fernando doesn't, I have written about that topic here. The question du jour is why the appositive in Sentence 3 gets a colon when the appositives in the other two sentences don't.
First of all, an appositive has to be at the end of a complete sentence in order to get a colon. So no colon for you, Sentence 1! But in Sentence 2 the appositive comes at the end of a complete sentence. Why doesn't it get a colon?
You set off an appositive with a colon when the whole point of the preceding sentence is to lead up to the appositive. In Sentence 3, the appositive chasing the mailman is the payoff of the sentence; the sentence exists to tell you what the dog's hobby is. In Sentence 2, the appositive, a skinny fellow with a handlebar mustache, is bonus information, an extra detail to help you better envision the real action, which is a dog chasing a mailman.
3. Use a colon to join independent clauses IF the second clause explains, expands, or illustrates the first. This one is a tad tricky. Last week, you may remember, I said that using a semicolon rather than a period signals that two independent clauses are more closely related than two separate sentences would be. The idea behind this use of the colon is that the two clauses are even more closely related than two clauses joined by a semicolon would be. The second clause, in this usage, is almost a repetition of the clause in front of it, in much the same way an appositive is a repetition of the noun in front of it.
It wasn't hard to see that Martha was a pirate: she had a peg leg, a black eye patch, and a parrot on her shoulder.
I don't often use the colon in this way because a semicolon will always be correct any place this usage of the colon would be correct, and I am more comfortable with semicolons than with colons (does that sound non-committal?).
4. Use a colon to introduce a quotation after an independent clause. This usage is especially helpful when you are introducing a quote from a book.
Wendell Berry argues that one of the dangers of the Machine Age is the tendency to start talking about people in mechanistic terms: "Our language, wherever it is used, is now almost invariably conditioned by the assumption that fleshy bodies are machines full of mechanisms, fully compatible with the mechanisms of medicine, industry, and commerce."
This use of the colon is unusual (though not unheard-of) in fiction and "creative non-fiction." If you write journalism or academic essays, however, you will find it especially useful.
5. Use a colon to introduce a "list of one." This was supposed to be a list of four, but it occurred to me that I had not accounted for one of the most common ways I use colons in these weekly letters. I often write something along the lines of, Consider the following example: The colon sets up an expectation, draws your attention to the example that I am about to provide. This use of the colon is really no different from Use #1 above, "Use a colon to introduce a list," except that there is only one item on the list.
Ok. We'll leave it there. Remember, any time you use a colon in prose, that comma needs to come at the end of an independent clause. The words after the colon may be an independent clause or they may not be (in most cases, they won't be). Next week, dashes, which, for better or worse, introduce even more punctuational flexibility than colons.