When to use parentheses

Parentheses are marks of punctuation used to separate a word, phrase, or sentence from the rest of a sentence.  Here are some suggestions on how to use them.

If the parentheses contain words which are part of a sentence but not a complete sentence themselves, don’t use a period or a comma within the  parentheses.  The exception is when the words within the parentheses are a question or an exclamation.  Then use a question mark or an exclamation point as appropriate.

• My mother (but not my father) has blue eyes.
• Both of my mother’s parents had blue eyes (no surprise there!).

If the words in parentheses are a complete sentence, use punctuation at the end of the sentence, within the parentheses. 

• My father and his mother had brown eyes. (But they each had at least one parent with blue eyes.)
• My father’s father had blue eyes. (So why didn’t my father have one brown eye and one blue eye?)

Parentheses within parentheses can be grammatically correct, but they can be confusing to the reader.  It’s a good idea to rewrite those ideas using one or no parentheses.

• I have brown eyes (the brown from my father (who probably had a recessive blue gene, like me)).
• I have brown eyes.  The brown gene came from my father, who probably had a recessive blue gene, as I do.

When a name can be reduced to its initials, say the complete name first, and immediately after the name put the initials in parentheses.  Later, when you use the initials in place of the name, you need to use an article in front of the initials.

• Both my mother’s parents were born in the United States (US), but neither of my father’s parents were born in the US.

When writing a research paper, you will be directed by your teacher to to use a particular style book.  That style book will have  information on how to use parentheses for citations and specific Latin abbreviations.  If you are not told to use a particular style book, you can use the Associated Press (A.P.) style book, or you can use a dictionary.  Name that book in the references part of your paper.

In general, it is better not to use parentheses if you can separate information with commas, or if you can rewrite idea to obviate the need for parentheses.  Too many parentheses can muddy the meaning, and the first rule in good writing is to be clear.