Like hot dogs and heartburn, parentheses and brackets always come in pairs. But unlike tube steaks and burps, parentheses and brackets are not at all the same.
You use parentheses much more often than you use brackets. Follow these rules for using these marks of punctuation correctly.
Use parentheses to set off nonessential information. In essence, the information in the parentheses is a nonessential modifier; it gives the reader additional information that's by no means crucial.
Use brackets for editorial clarification. And editorial clarification only.
Excerpted from The Complete Idiot's Guide to Grammar and Style © 2003 by Laurie E. Rozakis, Ph.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.