The Difference between Round and Square Brackets

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The Difference between Round Brackets and Square Brackets

Brackets are punctuation marks used in pairs. There are four types of brackets used in writing:
Type
Name
( )Parentheses or Round Brackets
[ ]Square Brackets or Box Brackets
{ }Braces or Curly Brackets
< >Angle Brackets or Chevrons
Read more about the four main types of brackets.

This page covers how to use round brackets (also called parentheses) and square brackets, which are, by far, the most common types of brackets used in writing. This infographic summarizes how round and square brackets are used:

the difference between round and square brackets

Round Brackets

Round Brackets for Additional Information

Round brackets are used to insert additional information in text. If you were to remove the brackets and the information inside, the text would still work. For example:
  • Set in the 17th century, The Three Musketeers ("Les Trois Mousquetaires" in French) is a novel by Alexandre Dumas.
  • Although they are relatively common off Australia, California, South Africa and Mexico, great white sharks usually inhabit coastal waters where the water temperature ranges 12-24 degrees Celsius. They generally hunt by detecting the electrical fields (They can detect less than one billionth of a volt.) emitted by the movements of their prey.

Period (Full Stops) Inside or Outside Round Brackets?

Writers often question whether punctuation, particularly periods (full stops), should be inside or outside a closed round bracket. The quick answer is that the punctuation follows logic. In other words, if the round brackets enclose a full sentence, then the period stays inside with its sentence. There are some quirks though. Here's some guidance:

Scenario 1: Bracketed non-sentence at the end of a sentence. When round brackets are used to insert information at the end of a sentence, the end punctuation of the sentence is placed outside the bracket. For example:
  • All the crew survived (even the dog).
Scenario 2: Bracketed sentence after a sentence. When the additional information is a standalone sentence that follows a sentence, then the whole thing including the end punctuation is placed inside the bracket. For example:
  • All the crew survived. (Even the dog survived.)
Scenario 3: Bracketed sentence inside another sentence. In a situation where the additional information is a standalone sentence within another sentence, then the end punctuation is usually omitted for readability. For example:
  • All the crew (The crew was four men and a dog) survived.

Round Brackets to Denote Singular or Plural

For brevity, round brackets can be used to show that a word could be either singular or plural. For example:
  • Please write the name(s) of your guest(s) in the section below.
  • Ensure the rod(s) is(are) aligned with the top section.
It is a common practice to give the plural option to only one word in the sentence and then treat the rest as singular. For example:
  • Please write the name(s) of your guest in the section below.
  • Ensure the rod(s) is aligned with the top section.

Don't Overuse Round Brackets

Using lots of brackets in your writing is usually a sign of bad sentence structure. Brackets also look a little informal in business correspondence.

Luckily, the latter issue is easily solved. You do not have to use brackets all the time. You have a choice between round brackets, commas, and dashes. These are all types of parenthetical punctuation. The information between a pairing of parenthetical punctuation is called a parenthesis.

Read more about parenthetical punctuation including brackets, commas, and dashes.

Square Brackets

Square Brackets to Make the Text Clearer

Square brackets can be used in a quotation to add information that explains the text it follows. (The square brackets show that the information has been added by someone other than the original author.) For example:
  • Hedy Lamarr once said: "Most people save all their lives and leave it [their money] to somebody else."
  • "It [electricity] is really just organized lightning."

Square Brackets to Modify the Original Text

Square brackets can also replace text in a quotation to make the quotation clearer for the reader. For example:
  • Hedy Lamarr once said: "Most people save all their lives and leave [their money] to somebody else."
Square brackets are often used in this way to make a quotation fit grammatically within another sentence. For example:
  • Alice Cooper famously said that "from the moment [he] leave[s] [his] house or hotel room, the public owns [him]."
  • (The original quotation said: "From the moment I leave my house or hotel room, the public owns me.")

Square Brackets: [sic]

The term [sic] is used to show that the word it follows featured in the original text. Often, [sic] is used to indicate that a grammar error in the text was written by the original author. For example:
  • The minister believed that his statement was "appropriate and did not undermine the moral [sic] of our troops."
    (This should be "morale" not "moral.")
  • Your demand for a "full compliment [sic] of men" cannot be met at this time.
  • (This should be "complement" not "compliment.")

Square Brackets: [...]

Ellipsis (three dots) can be used to show text omitted from a quotation. Ellipsis is usually written "..." or "[...]". For example:
  • It's no small irony that the government [...] ends up promoting precisely that which they would most like to repress.
    (The ellipsis replaces "inevitably and invariably.")
  • Andy Warhol is the only genius...with an IQ of 60.
  • (The ellipsis replaces the words "I've ever known" in this Gore Vidal quotation.)
Interactive Exercise
Here are three randomly selected questions from a larger exercise, which can be edited, printed to create an exercise worksheet, or sent via email to friends or students.

See Also

Using square brackets More about brackets, commas, and dashes What is parenthetical punctuation? What is a parenthesis?