What is the difference between 'brackets' and 'parentheses'?

Answer 1

Parentheses are round (like this); brackets are square [like this].

Parentheses are usually used in the citation of text with a work, such as citing a line, page number, or author. They are at the end of the quote.

Example: "The worst terrorist attacks in modern times to the United States have been Pearl Harbor and 9/11"(12).

Brackets are used to alter quoted text. It shows the reader that the alteration has been made. Usually used to change verb tenses or modify nouns, such as instead of him or her, a proper noun is used.

example: "The dogs have been digging a lot lately."

"The dogs [are] digging a lot lately."

Nested parentheses are ordered ([{hello}])--except in mathematics were they are ordered {[(x)]}.

The use of brackets and parentheses has nothing to do with "grammar" but rather with convention; different style guides may have slightly different rules on how to use them, so you must consult with the style guide that your editor or instructor prefers (e.g. Chicago Manual of Style, MLA Style Guide, etc.).