Parentheses ( ) are used to enclose nonessential or supplemental information in a sentence. Parentheses are always used in pairs; you must have both an opening and a closing parenthesis.

In formal academic writing, it is a good practice to use parentheses sparingly. Before including parentheses, check to see if they are essential. Could the information in parentheses be included as a subordinating clause surrounded with commas? Could the information in parentheses be a stand-alone sentence? If parentheses are needed, keep the following rules in mind.

  1. Use parentheses around nonessential information or abrupt changes in thought.
    • When the words in parentheses form a complete sentence, place a period inside the closing parenthesis.
      • No personal phone calls are allowed on company time. (Refer to the policy manual.)
    • When the words in parentheses are not a complete sentence, place the period outside the closing parenthesis.
      • The meeting will be held next year (in March).
    • Always place commas, semicolons, and colons outside the closing parenthesis.
      • The tasks consist of filling out paper work (including HR documents), setting up your email account, and getting a photo ID.
  2. If the information in parentheses requires a question mark or an exclamation mark, use the mark inside the parentheses only if the sentence ends with a different mark.
    • Richard Bender (remember him?) stopped by to see me yesterday.
    • Do you remember Richard (think you can remember back that far) from the bank?
  3. Use parentheses to clarify preceding words.
    • Next week we will study the hydrologic cycle (also known as the water cycle).
  4. Use parentheses for references or documentation of sources.
    • Fifty contracts were issued this year. (See Table 1.)
    • The U.S. leads the world in Internet use (Leslie 89).
  5. Use parentheses around an abbreviation or an acronym when it is used with the spelled–out word.
    • Please submit the Student Aid Report (SAR).
  6. Use parentheses in a horizontal list of items that uses either letters or numbers.
    • I need three items from the store: (1) apples, (2) bread, and (3) milk.
    • The following information must be included: (a) name, (b) address, and (c) driver's license number.
  7. Capitalize the first word in parentheses if it is a proper noun or the beginning of a complete sentence.
    • Verify all items. (Check the boxes.)
    • Call the assistant (Robert Digg) at noon.
  8. Use parentheses around numerals used with a spelled–out number.
    • I have ninety (90) dollars left from my paycheck.
  9. Use parentheses for minor subdivisions in alphanumeric outlines.
    • I.