Parentheses ( ) are grammar's way of letting a writer provide more information. Parentheses are always used in pairs. You can use parentheses to surround a word, a phrase or sentence fragment, a complete sentence, or many complete sentences.
It can be confusing to decide when or when not to use parentheses. You shouldn't put anything in parentheses that's integral to understanding the sentence.
Here's a trick for telling whether the information in your parentheses is necessary to understand the sentence: read the sentence back to yourself without what's in parentheses and see if it makes sense. If it does, you're likely using the parentheses correctly. If not, you're likely not.
- Incorrect Example: My mom and (her sister) decided to go on vacation.
- Correct Example: My mom (and her sister) decided to go on vacation.
In the first example, the parentheses were used incorrectly. Without parentheses, the sentence would have been My mom and decided to go on vacation, which doesn't make sense.
In the second example, without parentheses the sentence would have been My mom decided to go on vacation. This makes sense, so we know that and her sister are the correct words to put within the parentheses.