When do you use parentheses vs brackets in a sentence?

Parentheses and brackets are usually grouped under the term “other punctuation marks” in writing handbooks and resources. These two marks of graphics are used to set off material. Though sometimes confused or used in place of each other, their uses are specific, and using parentheses where brackets are required or vice versa would be seen as an error. In the Shawnee.edu Alternative Error Chart, misuse of parentheses appears as #25 at the list, occurring in only about 1% of student papers. Still, it is helpful to review some basics, including use of punctuation with parentheses and use of parentheses vs. brackets. Parentheses

Parentheses are always used in pairs—( )—opening and closing ones. They are used to enclose nonessential elements in a sentence and are often used where commas would also be appropriate. This supplemental, or parenthetical, material could be extra information, clarifications, asides, or citations, and the elements can be as short as a number or a word, or it can be as long as a few sentences (Kolln 92-93).

I stopped her and put a five-sou piece (a little more than a farthing) into her hand. ~ George Orwell (qtd in Kolln 267).

Ariel (published in 1965) contains Sylvia Plath’s last poems. (Little, Brown 412)

The parenthetical material must not be grammatically connected to the sentence containing it. Look at these examples from thepunctuationguide.com:

CORRECT: The president (and his assistant) traveled by private jet.

INCORRECT: *The president (and his assistant) were expected to arrive by 10:00 a.m.

This resource offers a simple test to see if you are making this mistake: “Simply read your sentence without the parenthetical content. If it remains grammatically correct, the parentheses are acceptable; if it doesn’t, the punctuation must be altered.” In the incorrect version, the subject of the sentence the president is singular, but the verb were is plural.

Placement of other punctuation with parentheses


Don’t put a comma before a nonessential element enclosed in parenthesis:

NOT: *The dungeon, (really the basement) haunted us.

BUT: The dungeon (really the basement) haunted us. (Little, Brown 412)

When a comma falls outside a parenthetical expression, it should be place outside the closing parenthesis, exactly as it would be if the parenthetical content were not there:

We verified his law degree (Yale, class of 2002), but his work history remains unconfirmed. (thepunctuationguide.com)

End punctuation

Common mistakes I see writers make are with placing end punctuation when using parentheses for supplemental material at the end of the sentence.

The rule is simple: if the parenthetical expression is part of the main sentence, the punctuation occurs outside the closing parenthesis:

After three weeks on set, the cast was fed up with his direction (or, rather, lack of direction).

If the parenthetical material is a sentence in its own right, the closing mark for that sentence is placed inside the closing parenthesis:

The idea that theoretical physics can be taught without reference to complex mathematics is patently absurd. (But don’t tell that to the publishers of such mathematics-free books⁠—or the people who buy them.)  

Do not use capitalization or a period when a complete sentence occurs in parentheses in the middle of a larger sentence, though use of a question mark or exclamation point is acceptable:

We verified his law degree (none of us thought he was lying about that) but not his billion-dollar verdict against Exxon (how gullible did he think we were?).

Finally, a special use of parentheses is for short translations in unquoted text: these can be placed in parentheses, although brackets are used for translations in quoted text.

His knowledge of Portuguese is limited to obrigado (thank you) and adeus (goodbye).

(Above points and examples adapted from thepunctuationguide.com)


Much less common than parentheses, brackets are used only in special cases. Like single quotation marks covered in an earlier post, they are used almost exclusively within quoted material.

Brackets are strong graphic marks which interrupt the text, alerting us that when we see them, we know the brackets and the information they contain have been added by someone else and are not part of the original author’s text.

Square brackets—[ ]—are always used in pairs and are placed around the change when writers insert or alter words in a direct quotation. They enclose any words that explain, clarify, or comment on the quote, sometimes helping to integrate it into the writer’s sentence.

Consider these examples:

“Four score and seven [today we’d say eighty-seven] years ago…”

“It [driving] imposes a heavy procedural workload on cognition that . . . leaves little processing capacity available for other tasks” (Salvucci and Taatgen 107).

A common error writers make is to use parentheses in place of brackets. Here is the second example with parentheses incorrectly used in place of brackets:

INCORRECT: *“It (driving) imposes a heavy procedural workload on cognition that . . . leaves little processing capacity available for other tasks” (Salvucci and Taatgen 107).

CORRECT: “It [driving] imposes a heavy procedural workload on cognition that . . . leaves little processing capacity available for other tasks” (Salvucci and Taatgen 107).

When integrating a quotation into your writing, you may use a signal phrase to introduce it. This makes the quote an integral part of your sentence so that you may have to change the quote so that it flows syntactically and logically.

Here is the original quote:

“The heavy cognitive workload of driving suggests that any secondary task has the potential to affect driver behavior” (Salvucci and Taatgen 108).

Here is the quote integrated into the writer’s text using brackets to indicate the change:

Salvucci and Taatgen propose that “[t]he heavy cognitive workload of driving suggests that any secondary task has the potential to affect driver behavior” (108).

As you can see, the upper case ‘T’ in the original has been changed to a lower case letter.

A Nancy Lewis cautions, material inserted into the brackets must fairly and accurately represent the quoted or original text, not be used to alter or add to it “in a way that twists the author’s meaning.

(All above examples from Lewis’s article, except for “The Gettysburg Address” quote, which is from grammarbook.com.)

There may be a rare occasion when parenthetical information may be needed with other parenthetical material. In this case, use brackets for the secondary parenthetical expression. As the punctuationguide.com says, this is one of the few uses of brackets outside of quotations:

In his twenties, he toured the country giving lectures to physics students (subsequently published as M-theory for Morons [2008]).

As discussed parentheses and brackets enclose material that explain, clarify, or comment on a text, whether parenthetical expressions (parentheses) or information related to a quote (brackets).

The use of brackets is specific and narrow, while parentheses have a wider use and flexibility. Parentheses can also be used in the place of commas, depending on the meaning and intent of the text.  As Kolln writes, a parenthetical structure “whispers, simply mentions in passing,” adding extra information or an aside. On the other hand, dashes, which can also be used in place of commas, emphasize, or shout, the message (93). We’ll look at the difference these choices make to your writing in a future blog.

 (Though labeled as wrong or incorrect, I continue to use the convention of an asterisk (*) to indicate an incorrect sentence.)

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