In rhetoric, a parenthesis (plural: parentheses; from the Greek word παρένθεσις parénthesis, which comes in turn from words meaning "alongside of" and "to place") or parenthetical phrase 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.
The following are examples of types of parenthetical phrases:
Introductory phrase: Once upon a time, my father ate a muffin.
Interjection: My father ate the muffin, gosh darn it!
Aside: My father, if you don’t mind me telling you this, ate the muffin.
Appositive: My father, a jaded and bitter man, ate the muffin.
Absolute phrase: My father, his eyes flashing with rage, ate the muffin.
Free modifier: My father, chewing with unbridled fury, ate the muffin.
Resumptive modifier: My father ate the muffin, a muffin which no man had yet chewed.
Summative modifier: My father ate the muffin, a feat which no man had attempted.
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.
