Periods like hanging out with full sentences. When there’s a set of parentheses in a sentence, the period follows the full sentence, no matter where the parentheses are. But periods aren’t the only parentheses punctuation you need to know — they’re just the most common.
- I invited Hugo (my best friend) to the wedding.
- Many students (including Isabel and Claire) felt sick after lunch.
That’s not too confusing. But what happens when the parenthetical expression falls at the end of a sentence?
- I invited Hugo to the wedding (he’s my best friend).
- Many students felt sick after lunch (including Isabel and Claire).
You only include periods inside parentheses when the parenthetical expression is a full sentence — and the sentence before it has already ended.
- I invited Hugo to the wedding. (He’s been my best friend since kindergarten.)
- Many students felt sick after lunch. (Isabel and Claire got the worst of it.)
Notice that you also capitalize the first letter of the parenthetical expression when you’re using it as a full sentence.
There shouldn’t be a time when you need to use two periods in a row, one inside the parentheses and one outside the parentheses. There are always more correct ways to write your sentences.
- Incorrect - I invited Hugo to the wedding (He’s been my best friend since kindergarten.).
- Correct - I invited Hugo to the wedding. (He’s been my best friend since kindergarten.)
- Also correct - I invited Hugo to the wedding (he’s been my best friend since kindergarten).
You’ve got the period rules down — good for you! Now forget all that, because adding other types of punctuation marks follows completely different rules.
- Have you seen my cat (gray, striped, meows a lot)?
- I can’t believe I failed that class (and after I studied all week)!
However, if the parenthetical expression has a different tone than the whole sentence, add the appropriate punctuation mark inside — even if it’s just a fragment or a word — to show the tone change.
- My cat is missing (have you seen her?) so we’re searching for her.
- I retook the class last week (even though I really didn’t want to!) and passed this time.
If the parenthetical expression ends the sentence, add a period after the parentheses to end the sentence (unlike the double period rule). It looks weird, but it’s correct.
- My cat is missing (have you seen her?).
- I retook the class last week (even though I really didn’t want to!).
Commas don’t go inside parentheses because they’re not terminal punctuation like periods, exclamation points, and question marks. You also never add a comma right before parentheses or right after parentheses.
You can use commas instead of parentheses to set off additional information. You just can’t use both parentheses and commas for the same purpose.
- Incorrect - Mr. Charles, (my math teacher) gave me a C.
- Incorrect - Mr. Charles (my math teacher), gave me a C.
- Incorrect - Mr. Charles (my math teacher,) gave me a C.
- Correct - Mr. Charles (my math teacher) gave me a C. (No commas)
- Also correct - Mr. Charles, my math teacher, gave me a C. (Commas replace parentheses)
You can use a comma right before parentheses when you’re making a numbered list within a sentence.
- We need a few things at the grocery store: (1) flour, (2) sugar, and (3) butter.
- John’s parents have four rules: (1) Be kind to your siblings, (2) Do your chores, (3) Do your homework, and (4) Be honest.
- There are three people I want on my team (among others): Fiona, Marcella, and Naomi.
- He forgot his umbrella (despite my many reminders); however, he did remember his coat.
Parentheses are just one of the many types of punctuation marks that add voice — and information — to your writing. Learn how to enhance your sentences with a few more handy writing conventions.