Parentheses and Brackets 101

Although parentheses and brackets look alike, they don't act alike. Before we get into their different roles, let's make sure we know which is which.

parentheses	brackets	braces
( )	[ ]	{ }

Parentheses, which have a similar function to commas and dashes, are probably the most commonly used of the three sets of punctuation above, followed by brackets and then the extremely rare braces. Here are some pointers on the right way to use them.

Use parentheses to enclose

• additional information that is not important enough to be set off by commas
  • Zooxanthellae (a type of algae) living inside the coral give it its brilliant hues and, through photosynthesis, provide 98 percent of its food.

    Note: Parentheses de-emphasize the information they enclose. If you would rather bring attention to that information, consider using em (long) dashes instead.

• individual letters
  • Print your name using the following formula: family name, surname, middle initial(s).
• letters or numbers in enumerations
  • Which of the following was not one of Antonin Carême's four mother sauces?
    (a) hollandaise
    (b) velouté
    (c) espagnole
    (d) béchamel
• subsection, paragraph, subparagraph, clause, subclause and sub-subclause numbers of legislation
  • Paragraph 47(1)(d) of the Public Service Employment Act makes reference to activities and obligations under the Employment Equity Act.

Do NOT use parentheses to enclose

• area codes in phone numbers

  WRONG: (310) 555-0176

  REVISED: 310-555-0176

Use square brackets to enclose

• editorial or explanatory notes in a quotation from another source
  
  • "The rate of the disease [tuberculosis] dropped from about 120 cases per 100,000 people in the 1940s, to 5.2 cases per 100,000 people in 2002."
• parenthetical information within parentheses
  
  • A major ferry rescue simulation was interrupted when two volunteers had to be evacuated for medical reasons. (A Times Colonist [October 16, 2006] article clarified that one volunteer was having an asthma attack while the other had been hit in the face by a door.)

  Note: In mathematical usage, this order is reversed: parentheses are placed within brackets, which are enclosed by braces.

For more information, see sections 7.29 through 7.37 of The Canadian Style.