Grammar Monster
Grammar Monster

The Difference between Round and Square Brackets

The Quick Answer
Round brackets ( ) are used to insert additional information.

Round brackets can also be used to show that something could be singular or plural, e.g., Remove the pin(s) from the leg.

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).
When the additional information is a standalone sentence among other sentences, then the whole thing including the end punctuation is placed inside the bracket. For example:
  • All the crew survived. (Even the dog survived.)
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 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.

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.

Square Brackets to Make the Text Clearer

Square brackets are used to add information that explains the text it follows. (The information is usually 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

Often, square brackets are used to replace text in a quote to make the quote clearer for the reader. For example:
  • Hedy Lamarr once said: "Most people save all their lives and leave [their money] to somebody else."
  • Alice Cooper famously said that "from the moment [he] leave[s] [his] house or hotel room, the public owns [him]."

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
    (should be "morale" not "moral")
  • Your demand for a "full compliment [sic] of men" cannot be met at this time.
  • (should be "complement" not "compliment")

Square Brackets: [...]

Ellipsis is used to show text omitted from a quote. 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 quote.)
Top Tip

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.

How Long Can Parenthesis Be?

Parenthesis is used to add additional information. Often, it is just a few words, but it can be a complete sentence or even a few sentences. (If it's any longer than that, you should probably reconsider whether it's appropriate as a parenthesis.)

Full Stops / Period Inside or Outside the Brackets?

In most cases, the full stop (period ) will be outside the brackets, but if your parenthesis is a complete sentence, it should start with a capital letter and end in a full stop / period, which would be inside the brackets.
  • Ashley likes cakes (especially cream cakes).
  • Ashley likes cakes. (He really likes cream cakes.)
So, it just follows logic. If the information inside the brackets is part of another sentence, treat it as such. If it's a sentence in its own right, treat it as such; i.e., give it its own full stop / period inside the brackets.

If the parenthesis is a complete sentence within another sentence, you can omit the full stop / period for style reasons. This is why there is no full stop / period after the word volt in the second example about sharks. Here's another example:
  • As the wine-growing season in France (We lived in France during my twenties) draws to a close, the festivals start.