Parentheses are punctuation marks that are used to set off information within a text or paragraph. Outside the realm of emoticons, parentheses always come in pairs. They can enclose a single word, a phrase, or even an entire sentence. Typically, the words inside the parentheses provide extra information about something else in the sentence.
Brackets, sometimes called square brackets, are most often used to show that words have been added to a direct quotation. Sometimes, when quoting a person or document, adding a word or two is necessary to provide enough context for the quote to make sense. For example, the original sentence you want to quote might read “We went and had a great time.” Out of context, this sentence doesn’t mean much. But you can add bracketed information to make the context clear.
It’s extremely important to use brackets when you change a direct quote—forgetting to add them results in a misquote.
Parentheses or Brackets With Surrounding Punctuation
Treat parentheses or brackets and the words inside them as separate from the rest of the sentence. Any sentence that contains a parenthetical element should still make sense if the element is removed.
Periods, question marks, and exclamation points should go before the closing parenthesis or bracket only if they belong to the words inside the parentheses or brackets. If the punctuation belongs to the surrounding sentence, put them outside the parentheses or brackets. Never put a comma immediately before a closing parenthesis.