Use brackets to enclose parenthetical elements in material that is itself within parentheses and to enclose explanatory words or comments that you are inserting into a quotation.

Brackets for material within parentheses

The investigation examined the major agencies (including the National Security Agency [NSA]) that were conducting covert operations.

Brackets for material within quotations

Massing notes that “on average, it [Fox News] attracts more than eight million people daily—more than double the number who watch CNN.”

The bracketed words clarify it in the original quotation.

In the quotation in the following sentence, the artist Gauguin’s name is misspelled. The bracketed Latin word sic, which means “so,” tells readers that the person being quoted—not the writer using the quotation—made the mistake.

One admirer wrote, “She was the most striking woman I’d ever seen—a sort of wonderful combination of Mia Farrow and one of Gaugin’s [sic] Polynesian nymphs.”