Brackets are like back seat drivers who constantly give directions--they have to get their "two cents" in. Unlike parentheses, which are "polite" backseat drivers, brackets yell their information by causing your eye to notice them.
Brackets are used in two cases:
- to add explanation, correction, or comment within a direct quotation
- Mamet said, "Another reason I want to go there [Turkey] is that my ancestors lived there for many generations."
- Note: You cannot add anything in brackets that changes the original meaning of the quotation.
Correct Incorrect Ivins states, "We know pre-school works. An 18-year follow-up study on pre-school done in Michigan [from 1978 through 1996] shows significantly lower rates of teen pregnancy, unemployment and incarceration" (A9). Ivins states, "We know pre-school works [in the best case scenario and among certain populations]. An 18-year follow-up study on pre-school done in Michigan shows significant lower rates of teen pregnancy, unemployment and incarceration" (A9).
- Note: Use the word "sic" in brackets (which is Latin for "thus it is written in the original") to show that you are reproducing a word or phrase exactly as it was written, despite an error.
- The ancient Tartars ate books "to acquire [sic] the knowledge therein."
- to act as parentheses within parentheses if you need to add information inside of the parentheses.
- Most doctors hail the good results the drug Prozac is producing in people struggling with depression. (But a recent study  suggests that the drug's side effects are debilitating for many.)