When deciding when to, or how to, use parentheses, an editor will first determine how important the information is to the sentence. At an initial glance, the rules for how to use parentheses may seem confusing, but they are relatively straightforward. You can find more information at http://www.ehow.com/how_4516252_use-parenthesis-writing.html.

Rule One:  

Unlike em dashes—which emphasize the words they mark—parentheses mainly enclose information that is not vital to a sentence. (Dashes emphasize, parentheses de-emphasize.) Regardless of the text within the parentheses, the sentence must still make sense if you delete them and everything inside.

Punctuation varies according to use, since both incomplete and complete sentences can reside happily within parentheses. If the sentence starts with an opening parenthesis, or the parentheses surround a complete sentence, an editor will put the terminal punctuation mark—the period, question mark, or exclamation point—inside the closing parenthesis.

Example: (I told her it would rain.)

If the text inside the parentheses is only a partial sentence, you will place the terminal punctuation outside.

Example: She went to England to find work (in 1972).

However, when you have a sentence that contains another complete sentence within parentheses, the punctuation is more complicated. If a writer wanted to add a complete sentence inside parentheses within another complete sentence, the terminal punctuation would go inside the parentheses, and another outside.

Example: She was soaking wet when she came back from her walk (They predicted rain!).

It is probably best to make the sentence within the parentheses a complete sentence or have a good reason for putting it in parentheses.

Rule Two:

Parentheses can be used to enclose words or figures that add clarity, additional information, or are used as an aside.

For clarification: “Last week I joined the SAG (Screen Actors Guild).”

For additional information: “When President Obama was inaugurated (January 20, 2009), there was a lot of excitement.”

In this case, the editor can ensure that the reader gets some additional information. But it isn’t a necessary part of the sentence. The main point is not to emphasize the date but the excitement, which is another reason to use parentheses, not dashes. (The parentheses de-emphasize the date; dashes would elevate it in importance.)

Another reason for using parentheses, in this case, is to avoid the comma within commas (i.e., between the date and year), which would make the sentence harder to read.

Using parentheses to include an aside is slightly different.

Example: I’m heading home early from the office tonight (Monday night football), but I’ll finish this work afterward.

“Monday night football” provides additional information to explain the speaker’s actions. Using commas would interrupt the flow of the sentence, and the phrase doesn’t seem important enough to the plot to use dashes. Using dashes instead of parentheses highlights the information instead of just providing background information.

Rule Three:

Parentheses can be used to enclose numbers or letters used for listed items. (1) We demand a pay rise, (2) we want longer lunch hours, (3) we want four weeks of vacation.

Square Brackets

Other elements of punctuation in the parentheses family include the square brackets. Not as common as the parentheses, they are useful when an editor or writer wants to put parentheses within parentheses. Two parentheses in a row would be confusing, so one set of square brackets are inserted around a clause within a clause inside the parentheses.

Example: “They went to Fiji for a month (they won the lottery [lucky people]).”

Square brackets also are also useful for scholars, authors, and editors who want to include comments, corrections, explanations, or translations that were not in the original text. If a writer quotes an expert, they can not alter the original quote. However, they can use bracketed words to clarify language.

Example: “The Mayor of Demby, upon learning of the scandal, sacked half of the town’s municipal workers.”

Since the original quote or the text written by the original writer can be clarified but not altered, this sentence couldn’t be changed to, “[Justin Rowley] sacked half of the town’s municipal workers.” Instead of replacing text, the square brackets would be used to clarify the text by writing, “The Mayor of Demby [Justin Rowley], upon learning of the scandal, sacked half of the town’s municipal workers.” Using square brackets adds clarifying information. Using parentheses around his name would be misleading because it would imply his name appeared in the original text as an aside.

In summation, authors, editors, and scholars use the parentheses mainly to include additional information or clarify existing information and establish a hierarchy of the importance of information in a sentence.

Originally posted 10/29/2011 and happily updated 10/26/2017. Thanks for reading!