Parentheses (always used in pairs) allow a writer to provide additional information. The parenthetical material might be a single word, a fragment, or multiple complete sentences.
Whatever the material inside the parentheses, it must not be grammatically integral to the surrounding sentence. If it is, the sentence must be recast. This is an easy mistake to avoid. Simply read your sentence without the parenthetical content. If it makes sense, the parentheses are acceptable; if it doesn’t, the punctuation must be altered.
Correct: The president (and his assistant) traveled by private jet.
Incorrect: The president (and his assistant) were expected to arrive by 10:00 a.m.
Placement of other punctuation
When a parenthetical sentence stands on its own, the closing punctuation mark for the sentence is placed inside the closing parenthesis.
The idea that theoretical physics can be taught without reference to complex mathematics is patently absurd. (But don’t tell that to the publishers of such mathematics-free books—or the people who buy them.)
When parenthetical content occurs at the end of a larger sentence, the closing punctuation mark for the sentence is placed outside the closing parenthesis.
After three weeks on set, the cast was fed up with his direction (or, rather, lack of direction).
When parenthetical content occurs in the middle of a larger sentence, the surrounding punctuation should be placed outside the parentheses, exactly as it would be if the parenthetical content were not there.
We verified his law degree (Yale, class of 2002), but his work history remains unconfirmed.
When a complete sentence occurs in parentheses in the middle of a larger sentence, it should neither be capitalized nor end with a period—though a question mark or exclamation point is acceptable.
We verified his law degree (none of us thought he was lying about that) but not his billion-dollar verdict against Exxon (how gullible did he think we were?).
Numbered or lettered lists should use a pair of parentheses to enclose the numbers or letters.
Please submit the following four items with your application: (1) a cover letter, (2) a resume, (3) a college transcript, and (4) a list of professional references.
Time zones are usually enclosed in parentheses following the time.
The conference call will be held at 9:00 a.m. (EST).
Area codes are sometimes enclosed in parentheses.
If you have any questions, please call me at (212) 555-7875.
Short translations in unquoted text can be placed in parentheses. (Use brackets for translations in quoted text.)
His knowledge of Portuguese is limited to obrigado (thank you) and adeus (goodbye).
In some writing, a person’s year of birth and year of death are provided in parentheses when the person is first mentioned. If there is uncertainty about the year, a question mark should follow it. Note that an en dash, rather than hyphen, is used between the years.
Guido Cavalcanti (1255?–1300) had a profound influence on the writings of Dante.
Abbreviations and acronyms
On the first use of an abbreviation or acronym that might not be understood by your readers, the full term can be provided in parentheses.
John Smith has been appointed CKO (chief knowledge officer) of the merged company.
In reverse, an acronym or abbreviation can be provided in parentheses upon its first use, and then used in place of the full term in the remainder of the document.
In conducting the study, researchers relied on positron emission tomography (PET) and, to a lesser extent, functional magnetic resonance imaging (fMRI).