Understanding the Uses of Parentheses

Parentheses—like commas, brackets, colons, and dashes—enclose a qualifying word, clause or phrase used as an explanation that clarifies, elaborate or comments upon the preceded element in a sentence Opens in new window.

A Parenthesis encloses element that is of secondary importance in writings. It can interrupt normal syntactic flow of the sentence but not necessarily affecting the sense. The parenthesis could be taken out and the surrounding elements still maintain correct grammatical sense.

Important Hint! 

Note that Parenthesis denotes the singular form, and Parentheses, the plural form.

Ways of using Parentheses

Rule #1a: Use parentheses [()] to enclose element of second importance

Use the bracket parentheses to enclose element that clarifies the surrounded elements or elements considered as a secondary thought or importance:

Examples include:
  • He finally answered (after taking five minutes to think) that he did not understand the question.
    If the texts in parentheses [()] ends a sentence, the period goes after the parentheses.
  • Gretchen likes coconuts (and fruits).

Commas could have been used in the first example; a colon could have been used in the second example. The use of parentheses indicates that the writer considered the information less important—almost an afterthought.

Rule #1b: Use parentheses [()] to include de-emphasize elements

Use parentheses [()] to include element that you want to de-emphasize or that wouldn't normally fit into the flow of your text but you want to include nonetheless.

If the material within parentheses appears within a sentence, do not use a capital letter or period to punctuate that material, even if the material is itself a complete sentence. (A question mark or exclamation mark, however, might be appropriate and necessary.) If the material within your parentheses is written as a separate sentence (not included within another sentence), punctuate it as if it were a separate sentence.

Examples include:
  • Thirty-five years after his death, Robert Frost (we remember him at Kennedy's inauguration) remains America's favorite poet.
  • Thirty-five years after his death, Robert Frost (do you remember him?) remains America's favorite poet.
  • Thirty-five years after his death, Robert Frost remains America's favorite poet. (We remember him at Kennedy's inauguration.)

If the material is important enough, use some other means of including it within your text—even if it means writing another sentence. Note that parentheses tend to de-emphasize text whereas dashes tend to make element seem even more important.

Rule #1c: Parentheses Within Parentheses

Use parentheses [()] to enclose a parenthetical remark within parentheses:

Example includes:
  • (We must still examine the mixture’s effects on several species [particularly, Ba, Cs, and Sr].)

Rule #2a

Use parentheses [()] to enclose a parenthetical remark containing a term requiring parentheses:

Example includes:
  • Initial experiments were performed with nonradioactive solutions. [e.g., solutions containing Ho (III)].

If the words inside the parentheses are a complete sentence, the period, question mark, or exclamation point that ends the sentence goes inside the parentheses:

Example includes:
  • Please read the summary of the events. (You'll be thrilled.)

This is a rule with a lot of wiggle room. A complete sentence inside the parentheses is often acceptable without an enclosed period:

Example includes:
  • Please read the analysis (you'll be amazed).

Rule #2b

Take care to punctuate correctly when punctuation is required both inside and outside parentheses.

Example includes:
  • You are late (aren't you?).
  • Note the question mark within the parentheses. The period after the parentheses is necessary to bring the entire sentence to a close.

Rule #3

Parentheses, despite appearances, are not part of the subject.

Example includes:
  • Joe (and his trusty mutt) was always welcome.
  • If this seems awkward, try rewriting the sentence:
     Joe (accompanied by his trusty mutt) was always welcome.

Rule #4

Commas are more likely to follow parentheses than precede them.

Examples include:

Incorrect Usage:

  • When he got home, (it was already dark outside) he fixed dinner.

Correct Usage:

  • When he got home (it was already dark outside), he fixed dinner.

Parenthesis Offset with Commas

When commas are used to offset a parenthesis, it keeps the focus on the surrounding text. As commas play other roles in sentences (e.g., to separate list items and to offset adverbial phrases), readers can sometimes become confused over where a parenthesis starts and ends.

Consider the following examples (where parenthesis is offset with commas) include:

  • Paul, on the other hand, is considered extremely trustworthy
  • House prices in Alton, which is only 25 minutes from London, are soaring.
  • Mathematics, rightly viewed, possesses not only truth but supreme beauty.

Also, if a parenthesis itself contains a comma or commas, it is advisable to avoid commas to offset it.

Examples include:

Incorrect Usage:

  • Dave Bellamy, like his father, Peter Bellamy, last year, was victorious in this year's regional pie-making finals.
  • (This could be confusing.)

Correct Usage

  • Dave Bellamy (like his father, Peter Bellamy, last year) was victorious in this year's regional pie-making finals.
  • (This version is clearer.)

Parenthesis Offset with Dashes

When dashes are used to offset a parenthesis, it increases the focus on the parenthesis.

Examples include:
  • They roasted the winning brisket — the size of pillow — in a mighty clay oven.
  • If mankind minus one were of one opinion, then mankind is no more justified in silencing the one than the one — if he had the power — would be justified in silencing mankind.
  • (attributed to John Stuart Mill, 1806-1873)
Further Readings: Parentheses & Brackets Opens in new window
Philip Rubens; Science and Technical Writing: A Manual of Style Opens in new window Parentheses Opens in new window What Is Parenthesis? Opens in new window