In honor of National Punctuation Day, learn how to use colons.
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Today's topic is how to use colons.
One of my favorite grammar books, titled* Punctuate It Right, has a wonderful name for the colon: the author calls it the mark of expectation or addition (1). That's because the colon signals that what comes next is directly related to the previous sentence.
Here are some occasions when you might need to use a colon. We'll talk about each situation more in detail below.
1. Use colons after complete sentences
2. Use colons to format lists
We'll also talk about two frequently asked questions that come up around colons, specifically:
1. How many spaces to use after a colon
2. How to capitalize after a colon
Use Colons After Complete Sentences
The most important thing to remember about colons is that you only use them after statements that are complete sentences. Never use a colon after a sentence fragment.
For example, it's correct to say, "Grammar Girl has two favorite hobbies: watching clouds and seeing how long she can stand on one foot." That's correct because "Grammar Girl has two favorite hobbies" is a complete sentence all by itself.
Notice how the items after the colon expand on or clarify what came before the colon. I referred to my favorite hobbies before the colon and then specifically named them after the colon. A quick and dirty way to decide whether a colon is acceptable is to test whether you can replace it with the word namely. For example, you could say, "Grammar Girl has two favorite hobbies, namely, watching clouds and seeing how long she can stand on one foot." Most of the time, if you can replace a colon with the word namely, then the colon is the right choice.
Let's go back to the complete-sentence issue: it would be wrong to say, "Grammar Girl's favorite hobbies are: skiing and reading" because "Grammar Girl's favorite hobbies are" is not a complete sentence by itself. (And, really, who would rather ski than stand on one foot?) You can often fix those kind of sentences by adding the words the following after your sentence fragment. For example, it would be fine to say, "Grammar Girl's favorite hobbies are the following: skiing and reading" because you've made the thing before the colon a grammatically complete sentence by adding the words the following.