In rhetoric, a parenthesis (plural: parentheses; from the Greek word παρένθεσις, which comes in turn from words meaning "alongside of" and "to place") is an explanatory or qualifying word, clause, or sentence inserted into a passage. The parenthesis could be left out and still form grammatically correct text. Parentheses are usually marked off by round or square brackets, dashes, or commas.
- Billy-bob, a great singer, was not a good dancer.
- The phrase a great singer, set off by commas, is both an appositive and a parenthesis.
- A dog (not a cat) is an animal that barks.
- The phrase not a cat is a parenthesis.
- My umbrella (which is somewhat broken) can still shield the two of us from the rain.
- The phrase which is somewhat broken is a parenthesis.
- Please, Gerald, come here!
- Gerald is both a noun of direct address and a parenthesis.
While a parenthesis need not be written enclosed by the curved brackets called parentheses, their use principally around rhetorical parentheses has made the punctuation marks the only common use for the term in most contexts.
- John Walker (1823). A Rhetorical Grammar: In which the Common Improprieties in Reading and Speaking are Detected .... T. Cadell. p. 99.