Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Brackets
Other punctuation marks
Punctuation

Use brackets to enclose any words or phrases that you have inserted into an otherwise word-for-word quotation.

Audubon reports that “if there are not enough young to balance deaths, the end of the species [California condor] is inevitable” (4).

The sentence quoted from the Audubon article did not contain the words California condor (since the context of the full article made clear what species was meant), so the writer needed to add the name in brackets.

The Latin word “sic” in brackets indicates that an error in a quoted sentence appears in the original source.

According to the review, Lizzo’s performance was brilliant, “exceding [sic] the expectations of even her most loyal fans.”

Instead of using “sic,” the writer could have paraphrased the quotation: According to the review, even Lizzo’s biggest fans were surprised by the brilliance of her performance.

NOTE: For advice on using “sic” in MLA and APA styles, see 56b and 61b, respectively.