Parentheses and brackets set off portions of text from the whole for various purposes.
Parentheses, appearing almost exclusively in pairs, are usually employed in the same manner as a pair of commas or dashes, though they suggest de-emphasis of the content within (as opposed to commas, which convey a neutral insertion of information, and dashes, which highlight the text between them).
Parentheses, in addition to being employed to interject examples or a brief digression, enclose an abbreviation, acronym or initialism; a translation; or a numerical equivalent of a spelled-out number.
They also can set off a cross-reference, as in: “For more details, read the associated case study (pages 113–119)” or “Gene therapy is discussed briefly here. (See chapter 12 for more information.)”
Parentheses might frame a plural ending to indicate that a word can be read as either singular or plural, as in “Enter the title(s) of the document(s) on the asset list,” or to allow for a gender-neutral reading, as in “Next, (s)he should consult with an adviser.”
Note that one of a pair of parentheses is called a parenthesis. This term also pertains in general to setting text off from other text regardless of which punctuation signals the separation. (Two or more instances of parenthesis might be referred to as parentheses.) Text that is set off by complementary punctuation marks is sometimes referred to as a parenthetical phrase, or simply a parenthetical.
A single close parenthesis is sometimes used in place of a period when enumerating, as in “The three types of rock are 1) igneous, 2) metamorphic and 3) sedimentary.” (The open parenthesis is not used in isolation.)
A few more guidelines about parentheses follow:
- Parentheses should not be used in immediate proximity to each other or within another set of parentheses; in the latter case, use brackets (or commas or dashes) instead.
- Avoid including more than one sentence, or including an extensive sentence, within parentheses.
- Avoid situating a complete sentence in parentheses within another sentence.
- Avoid using parentheses too frequently. Consider employing commas or dashes instead, or otherwise revising text so that parentheses do not appear repeatedly in one piece of content.
- Parentheses framing text in italics, boldface or another style treatment differing from the default text should not share that formatting, but should rather be in the same font as the surrounding text.
A complete sentence within parentheses should end with a period or other terminal punctuation before the close parenthesis, and the preceding text should be followed by terminal punctuation:
“. . . then it is fair game. (There are always exceptions, of course.)”
If text enclosed in parentheses does not comprise a complete sentence and ends a framing sentence, the terminal punctuation of the framing sentence should immediately follow the close parenthesis.
“. . . then it is fair game (with exceptions).”
Text in parentheses in the midst of a sentence is not punctuated, regardless of whether it is a complete sentence (unless the terminal punctuation is a question mark or an exclamation point), and the first word of a complete sentence in parentheses is not capitalized:
“. . . then (there are always exceptions, of course) it is fair game.”
“. . . then (with exceptions) it is fair game.”
Brackets, in American English, refer to square brackets. (In British English, the term pertains to round brackets, or what in American English are called parentheses.) Brackets have limited uses, including:
- adding contextual information within quoted material “She spoke to [Smith],” where the bracketed text replaces one or more spoken words to provide clarity (in this example, replacing the vague him) or to add a word or phrase omitted in the spoken or written quotation. Sometimes, the replaced word or phrase is retained, as in “She spoke to him [Smith],” but this is unnecessary.