PARENTHESES

Rule 1. Use parentheses to enclose words or figures that clarify or for an aside.

Examples I expect five hundred dollars ($500).

He finally answered (after taking five minutes to think) that he did not understand the question.
Commas could have been used in the above example. Parentheses show less emphasis or importance. Dashes could also have been used instead of parentheses to show emphasis.

Rule 2. Use parentheses to enclose numbers of listed items in a sentence.

Example We need a telephone operator who can (1) think quickly, (2) remember not to leave people on hold, and (3) handle complaints from the public. Periods or half parentheses are acceptable also.

Rule 3. Periods go inside parentheses only if an entire sentence is inside the parentheses.

Example Please read the analysis (I enclosed it as Attachment A.). OR
Please read the analysis. (I enclosed it as Attachment A.) OR
Please read the analysis (Attachment A).