英语语法：220 Parentheses, Brackets, and Braces

Grammar Girl here.

Today guest-writer Bonnie Trenga will help us talk about three punctuation 1 marks: one you undoubtedly 2 know how to use, another you possibly misuse 3, and yet another you’ve likely never used. If you’ve ever wondered when to favor parentheses 4 over square brackets and when to stick in a pair of curly braces 5, listen on.

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Parentheses

You’re probably well versed 6 in how to use those sideways eyebrow 7 thingies, better known as parentheses. First, remember that a pair of them is called “parentheses,” whereas a single one is a “parenthesis 8.” You may want to review episode 222 in which we compared parentheses to dashes and commas. For now, let’s just say that parentheses mainly enclose information that is not vital to a sentence. No matter what you put within parentheses, your sentence must still make sense if you delete them and everything inside. Note that you are allowed to put both partial sentences and complete sentences within parentheses. But no more than a whole paragraph, please, requests authority Brian Garner 9 (1).

Before we move on, we need to address one issue: how to use terminal punctuation marks with parentheses. If your sentence starts with an opening parenthesis, then what’s inside your parentheses is a complete sentence. You must therefore ensure that the terminal punctuation mark, such as a period, question mark, or exclamation 10 point, goes inside the closing parenthesis: “(I knew he wouldn’t want to do that.)”. If what’s within the parentheses is only a partial sentence, put the terminal punctuation outside instead: “I moved to America when I was 10 (in 1980).”

For the most part, these two rules seem fairly easy to understand—complete sentence: terminal punctuation inside; partial sentence: terminal punctuation outside. However, when you have a sentence that contains another complete sentence within parentheses, the punctuation could become confusing. Let’s say you want to add the complete sentence “I can’t believe it!” inside parentheses within another complete sentence. In this case, the exclamation point would go inside the closing parenthesis and then a period would go outside: “I ate the whole box of donuts (I can’t believe it!).”

That works, but I often recommend making the sentence inside parentheses a complete sentence on its own that follows the first sentence. Make sure you have a reason for putting it in parentheses.

Square Brackets

Now it’s time to introduce our potentially misused 11 friends: square brackets. Brackets, which are one long line short of a standing-up rectangle, appear on the keyboard to the right of the letter “p.” They seem less common than their parenthetical cousins, though you do sometimes see both punctuation marks within the same sentence. Use brackets in sentences where you want to put parentheses within parentheses. Since two parentheses in a row would be confusing, you bookend your parentheses with brackets. So, the order is opening parenthesis, opening bracket, closing bracket, closing parenthesis. For example, you would write “They are getting married (they love each other [of course!]).”*

According to Garner, square brackets also come in handy for subsequent authors and editors who want to “enclose comments, corrections, explanations, interpolations, notes, or translations that were not in the original text” (2).

If you are in a scholarly field, you may find yourself writing a paper and quoting an expert, and perhaps you discover you need to clarify what the expert said. Bill Walsh in Lapsing 12 into a Comma (3) warns, “Bracketed material should clarify language, not replace it….” You shouldn’t alter what the original writer wrote, so use brackets around your clarification. For example, if the original quotation 13 reads, “This enterprising paleontologist discovered a new species of plant eater,” you shouldn't change it to “[Bob Jones] discovered a new species of plant eater.” You’d have to quote the material this way: “This enterprising paleontologist [Bob Jones] discovered a new species of plant eater.” (Note also that you wouldn’t be allowed to use parentheses around the name you add, because it would seem—incorrectly—like an aside that appeared in the original text.)

Remember, though, that brackets differ from the three dots called an ellipsis 14, which you use when you are deleting extraneous 15 words from a direct quotation. If you want to learn more about an ellipsis, see the recent Grammar Girl episode on ellipses 16.

Sometimes you might decide to start a sentence by quoting someone, but the quotation does not include a capital letter. If your work is informal or not overly formal, it is acceptable to just change the lowercase letter to a capital one. On the other hand, scholars who must be “rigorously accurate” (4) are required to use a set of brackets around the capital letter they are changing. For example, if the quoted word is “it,” with a lowercase “i,” and a rigorously accurate scholar wants the word “it” to start a sentence, she would have to write bracket-uppercase I-bracket-lowercase t: “[I]t.”

The last place you are likely to encounter square brackets is around the Latin word “sic,” which means “thus.” You use it—in italics—when you’re quoting someone who has made an error, such as a misstatement of fact or a spelling mistake. You should use bracket-sic-bracket only when you need to aid readers (5); you don’t want to show off or seem pedantic 17 by constantly pointing out others’ failings. Admittedly, though, we grammar types understand this urge to correct others.

Braces

Our last foray into punctuation marks leads us to what are known as curly braces. To type one, press the shift key as you punch the bracket key, to the right of the letter “p.” I must say I have never used curly braces. In fact, although they looks like punctuation marks, they really aren’t (6), at least not in the way you can type them yourself.

They’re on your keyboard because they have specialized 18 uses in mathematics and science. For example, they are used to enclose the third level of nested equations when parentheses and brackets have already been used for the first two levels (7).

Big curly braces that span multiple lines are sometimes used to enclose groups of words that belong together (8) or triplet lines in poetry, but your keyboard doesn’t have those big curly braces that span multiple lines.

Summary

Today you’ve learned how to use various curved, square, and curly squiggles within your sentences. Be sure to keep them straight!