In honor of National Punctuation Day, learn how to use colons.
Chicago Style: Complete Sentences and Less Capitalization
Next, let’s look at the colon rules from the Chicago Manual of Style. They’re similar to APA in that they only allow you to use a colon after something that could stand alone as a complete sentence.
For example, it's correct to write, "Grammar Girl has two favorite hobbies: watching clouds and seeing how long she can stand on one foot." That's correct in Chicago style because "Grammar Girl has two favorite hobbies" is a complete sentence all by itself.
And let’s think for a minute about why we use colons. Why is it appropriate in this sentence?
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 Tip for deciding whether a colon is a good choice 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 words “namely,” or “it is,” or “they are,” then the colon is the right choice.
Where Chicago differs from APA style is that in Chicago style, you’re only supposed to capitalize the first letter after the colon if it’s the start of at least two complete sentences. If it’s just one sentence in Chicago, you keep the first word lowercase.
Therefore, you’d capitalize the word “she” in the following sentence because it’s the start of a two-sentence series:
Grammar Girl has had many hobbies over the years: She used to love watching clouds. Today, however, she prefers to use colored pencils to fill in all the round letters she finds in magazines.
But in Chicago style, you wouldn’t capitalize “she” in “she used to love watching clouds” if you ended the description of Grammar Girl’s hobbies after “she used to love watching clouds” because then there’s only one sentence after the colon:
Grammar Girl has had many hobbies over the years: she used to love watching clouds. (correct in Chicago style)
Grammar Girl has had may hobbies over the years: She used to love watching clouds. (incorrect in Chicago style)
To summarize, in Chicago style, you use colons only after complete sentences and you capitalize the first word after a colon only if it’s the start of at least two complete sentences or is a proper noun.