Parentheses are used to enclose incidental or supplemental information or comments. The parenthetical information or comment may serve to clarify or illustrate, or it may just offer a digression or afterthought. Parentheses are also used to enclose certain numbers or letters in an outline or list.
1. Use parentheses to enclose additional or supplemental information that clarifies or illustrates a point.
In a business letter the salutation and body of the letter are flush left (against the left margin).
Everything that went wrong that day (the accident, the missed appointment, the argument) was eventually forgotten in the midst of the joyful celebration.
2. Use parentheses to offer a digression or afterthought.
The mayor should apologize for his angry outburst (so typical for someone caught in a lie) at the meeting last night.
Your use of citations in the last paper (which was beautifully written, by the way) offered a good example of how to avoid plagiarism.
3. Use parentheses to enclose numbers or letters introducing items in a list or outline.
There are five steps to cleaning an aquarium: (a) Put the fish somewhere else; (b) drain the water out; (c) scrub the inside of the glass; (d) add dechlorinated fresh water; and (e) return the fish.
4. Punctuate parenthetical material according to the following guidelines:
His family's arrival (they had never called us) was a surprise.
I am certain we saw a ghost (Have you ever seen one?) on the stairs that night.
We were all frightened (My husband was terrified!) by the image we saw.
Should I invite him by telephone (very politely, of course)?
When Frances sat down next to Ducky (her cat), she was very careful not to sit on her tail.
For years, his brother desperately wanted that car. (He finally gave it to him!) It was a 1948 Buick in mint condition.
Note: Refer to the TIP Sheets on "The Comma," "The Hyphen," and "The Dash, Slash, Brackets, and Ellipsis" to help you differentiate among the uses of parentheses and these other various punctuation marks.