English Grammar for the Utterly Confused - Laurie Rozakis 2003
Brackets
Chapter 10 Punctuation
Part 4 A Writers Tools
Brackets are [ ]. Do not confuse them with parentheses, which are curved like this (). Brackets have only two very narrowly defined uses.
1. Use brackets for editorial clarification.
Children’s author Jackie Ogburn puts it this way: “It’s not that ’message’ isn’t a part of the work. It’s just that it’s usually the least interesting part [emphasis hers].”
2. Use brackets to enclose words that you insert in a quotation.
When you integrate quoted words into a text, you may have to change a few words to fit the structure of your sentences. Enclose any changes you make in brackets.
Original quote: “This pedagogical approach reduces all our work to the literary equivalent of vitamins.” (Ogburn 305)
Quotation with brackets: The primary reason the people involved in creating children’s books detest this attitude so much is that “[it] reduces all our work to the literary equivalent of vitamins.” (Ogburn 305)