I assumed it was for information only and not actually spoken by the person being quoted, but I have tried taking out the words within the brackets and often it makes no grammatical sense at all. Jayne Blake
If something is missing, because it is unable to be read or torn out of a page (as in old documents), the translator or editor puts what is assumed to be the missing piece in square brackets. It isn't always totally right, but it is inserted (as you have found) to make sense of the quote.
Usually, square brackets enclose a paraphrase or clarification of what the person actually said. Let's say I actually said John helped me write the book, but the audience would have no idea who John is, so the newpaper might quote me as saying [My brother] helped me write the book. Another use might be if you need to change the tense of a verb to fit a quote into a larger statement. For example, an author wrote: Every time I go to Yellowstone, I see buffalo. (But this happened many years ago.) So you might quote it as: He said that everytime I [went] to Yellowstone, I [saw] buffalo. (The change in tense might be important if you want to then say that nowadays, this is not true any more.) Using brackets this way is a fair way of clarifying quotes.
Usually the use of square brackets and curly brackets is to enable the use of parentheses within parentheses without confusing where the superior and subordinate sentences end.
The words in brackets are implied information based on what was actually said and they sometimes replace a word or 2 with the bracketed words (Or rewrite the sentence to make it work better), which is why it doesn’t make sense when you remove the bracketed phrase Example: SOURCE: The boy sped up, passed the pedestrian, and turned the corner. ARTICLE: The witness reported that she’d seen “[t]he boy [speed] up.” Or, to borrow an answer from Yahoo Journalists use brackets within quotations to put words in people’s mouths. This isn’t necessarily a bad thing! Sometimes journalists have to insert words to help to clarify a statement. Brackets are often used to identify ambiguous pronouns in a direct quotation. For example: They [the 8th Federal Infantry] fought bravely under the most adverse circumstances during the Civil War. You can also use brackets to properly place a quote within the syntax of a sentence. To decapitalize a word, for example, Doctor Fielding’s written opinion states that ’[p]atients are often deceitful.’ Square brackets are also used in conjunction with the [sic] punctuation, which is a way of distancing yourself from a misstatement or a misspelling. For example, The Delaware River is indeed a truly majestic site [sic]. Finally, to quote usage guru Bryan Garner (and conveniently use square brackets in the process), [Square brackets] enclose comments, corrections, explanations, interpolations, notes, or translations that were not in the original text but have been added by subsequent authors, editors, or others.
