Parentheses always come in pairs (opening and closing).
Parenthetical information is non-essential. If the sentence is clear without it, parentheses are appropriate (or commas or em dashes).
If what is enclosed is a separate, complete sentence, its ending punctuation falls just before the closing parenthesis. Otherwise, any required punctuation (comma, question mark, period, etc.) follows the closing parenthesis.
- That particular weekend, we drove separately. (Trevor took the truck, and I came in the car.
- She retired from teaching Adult Basic Education (ABE) classes. (She taught for fifteen years.)
- Every weekend (Saturday and Sunday), we went to the mountains.
- We went to the mountains every weekend (Saturday and Sunday).
- Probably the most famous cigar smoker was George Burns (1896–1996).
- I do not recall previous presidents using POTUS (President of the United States).
Other uses include time zones, area codes, and short translations.
- When the phone rang, she calculated the time for the caller, 4:00 p.m. (EST).
- This was not her daughter’s number, (123) 456-7890.
- Almost everyone knows a little Spanish: adios (goodbye) and gracias (thank you).
To show a formal (numbered or lettered) list, enclose the numbers/letters in parentheses.
Please follow the proper procedure for resetting your clock: (1) press the “time” button, (2) simultaneously press the “hour” button as necessary to change the hour, (3) release the “hour” button and continue to hold the “time,” (4) press the “min” button as necessary to change the minutes, (5) release all buttons.
Brackets serve as parentheses within parentheses.
Every weekend (Saturdays [unless Tommy was playing football] and Sundays), we went to the mountains.
We had a wonderful time (except for the shark attack [actually, no big deal]) at the beach.
Use brackets instead of parentheses inside quotations.
“Humpy Dumpty [an egg] sat on a wall.”
“Only two things are infinite [having no end], the universe and human stupidity, and I’m not sure about the former” (Albert Einstein).
To indicate an error or confusion in an original quotation, insert an italicized “sic” between non-italicized brackets (or the reverse if the quotation is in italics).
The handwritten note was sent to all the classrooms, “Students, report too [sic] the auditorium.”
Nobody found the typo in the quotation from Harlan Ellison so it was quoted in the newspaper as “The too [sic] most common elements in the Universe are Hydrogen and Stupidity.”