Use parentheses (or round brackets) to set off explanatory or supplementary information from surrounding text.
- The only living monotremes (egg-laying mammals) are platypuses and echidnas.
The text enclosed in parentheses should not be essential to the grammar of the sentence.
- Incorrect: Parentheses (or round) brackets enclose optional but useful information.
Correct: Parentheses (or round brackets) enclose optional but useful information.
Correct: Parentheses or (round) brackets enclose optional but useful information.
Periods and other punctuation marks go within parentheses if they belong to the parenthetical matter but outside if they belong to the larger sentence.
- Correct: Call them tomorrow (or perhaps on Monday).
Correct: Call them on Monday. (They’re closed on weekends.)
Use square brackets within parentheses to show nested brackets. (In British style, round brackets are used (like this); avoid nested parentheses in U.S. style.)
- Monotremes (egg-laying mammals [e.g., platypuses]) are now found only in Australia and New Guinea.
Parentheses are stronger than commas but less forceful and more formal than dashes.
What are parentheses (round brackets)?
Parentheses (or round brackets) are punctuation marks used mainly to set off explanatory or supplementary information, which can comprise words, phrases, clauses, or entire sentences.
- Plant-based marine organisms (like seaweed and plankton) produce half the world’s oxygen.
- Lulu bakes all kinds of confectionary (cookies, cakes, cupcakes, etc.).
- Parentheses are also known as (round) brackets.
- Slashes (or virgules) may be used to present options.
- Maya likes descriptive place names (like the settlement in New Jersey called Quibbletown).
- She grew up in a tiny town called Nusquam. (It was nowhere you could find on a map.)
Parentheses are stronger than commas and similar to but less forceful than dashes. In this article, we discuss how to use parentheses correctly and how they differ from other punctuation marks.
A note on spelling: An opening parenthesis (singular) and a closing parenthesis together make a pair of parentheses (plural).
To set off additional information
Use parentheses to mark off explanatory information that is not essential either to the meaning or to the grammar of a sentence. Such information may be useful or interesting but is tangential to the main point of the passage.
- Amphibians (toads, frogs, salamanders, etc.) can breathe and absorb water through their skin.
- We buy and sell all types of vehicles (SUVs, trucks, sedans, etc.).
- My cat Tooks (a cheese lover like me) loves pizza.
- Dark energy (see Chapter 4) explains the expansion of the universe.
- Making money is his (only) passion.
- The cat (she had been awake since 4 a.m.) finally fell asleep when we woke up.
- Please make sure to water the plants, feed the cat, walk the dog, and leave our apartment cleaner than you found it. (Cleaning supplies are in the closet.)
Also use parentheses to provide supplementary information that may be useful to the reader. Such details should be structurally independent from the sentence (i.e., not grammatically necessary to complete the sentence).
- The number of site visitors was higher in May (Table 1).
- Each of the questions was assigned a weight (see Appendix A).
- Parentheses may enclose an entire independent clause. (An independent clause can stand by itself as a sentence.)
Don’t use parentheses to enclose words or phrases that are grammatically necessary to the sentence.
- Incorrect: My cat (loves cheese) and pizza.
Without the parenthetical text, the sentence would be rendered ungrammatical (“My cat and pizza”?).Correct: My cat (who loves cheese) likes pizza.
The sentence would still be grammatically complete and make sense without the parenthetical text (“My cat likes pizza”).
To mark an afterthought
Parentheses may be used to set off an afterthought.
- Honesty is the best policy (or so they say).
- He claims his messages were accidentally deleted. (Any jury will find that hard to believe.)
- Let’s order a cake (chocolate or butterscotch?) and balloons.
- It was I who sent the message. (Wasn’t that obvious?)
- My father (at least the man who claims to be my father) called this morning.
A postscript does not need to be enclosed in parentheses. The abbreviation P.S. already indicates that the text is an afterthought.
To introduce an abbreviation or definition
Use parentheses to introduce an abbreviation or other term in text. Parentheses may also be used to provide a definition.
- Unsinkable floating devices (UFDs) have saved numerous lives on sea.
- You will need to contact your DNS (domain name system) server.
- Two closely connected independent clauses (clauses that can stand by themselves as sentences) may be joined using a semicolon.
- Watercraft that could operate underwater (submarines) were instrumental in winning the war.
When you introduce an abbreviation in a document, provide the full form and then the abbreviation in parentheses. However, if the abbreviation is better known than its full form, you may provide the abbreviation first and then its full form in parentheses.
- Fourteen different bird species were found in a single SGS (small green space).
- The world’s first PC (personal computer) was sold in 1971.
In source citations
Parentheses are used in bibliographic citations in various citation styles.
- Minerva Dash, On Silence (London: John Wiley & Sons, 1983), 22.
- Femy, R. (2013). The complete guide to cat behavior (Vols. 1–3). New York, NY: Dash Publishing.
In-text citations are set off from surrounding text by parentheses.
- Research has revealed that breathing between sips of green tea can extend your life span (Blake 1965, 321–2).
With periods and other punctuation
Place other punctuation marks (like periods, question marks, exclamation points, and quotation marks) within parentheses if they belong to the parenthetical matter, but after the closing parenthesis if they are instead part of the larger sentence.
- If you can fit a sports car in a hippo’s jaws (is that true?), you can do anything.
- You can fit a sports car in a hippo’s jaws. (Is that true?)
- Poco (that guy you met at the party) told me the whole sordid story.
- The world’s oldest wooden wheel is 5,000 years old (give or take a few centuries).
- Could you call him (or at least send him a text)?
- She writes, “Happiness is easily found (and just as easily lost).”
- The world’s oldest wooden wheel is 5,000 years old. (It was found in 2002 near Ljubljana.)
A comma at the end of parenthetical matter always goes outside parentheses. (It is always part of the larger sentence.)
- I asked her (casually, over breakfast), and she said she didn’t know.
- We have offices in Albany (NY), Oakland (CA), and Wilmington (DE).
Periods in particular can be confusing. Place a period within parentheses if the entire sentence is in parentheses. If only part of the sentence is enclosed in parentheses, place the period outside.
- We can send them the report next week. (It’s due the week after.)
- We are open all year round, except Wednesdays, weekends, and windy days in winter. (We are human after all.)
- We can send the report next week (or even the week after).
- We can send the report next week (it’s due the week after).
- We are open all year round (except Wednesdays, weekends, and windy days in winter).
When an abbreviation ending in a period appears within parentheses at the end of a sentence, place another period after the closing parenthesis to mark the end of the sentence. But if the abbreviation ends a sentence entirely contained within parentheses, don’t add another period after.
- I’ll call you tomorrow morning (around 6 a.m.).
- This is a study on pollinators (bees, birds, butterflies, etc.).
- I’ll call tomorrow morning. (I hope you’re up by 6 a.m.)
- We still have to finalize the menu for the party. (We also need to buy buntings, banners, balloons, etc.)
Entire paragraphs of text may be enclosed in parentheses. This is seen mainly in creative writing, where the author may want to provide tangential but interesting information to the reader. In formal writing (such as academic and business texts), avoid enclosing a paragraph in parentheses. Instead, provide supplementary information in an appendix to your thesis or report and refer to it parenthetically in the main text.
- Participants’ responses were then categorized as biased or unbiased (see Appendix C).
Brackets within parentheses
To show parenthetical material inside text already within parentheses (brackets within brackets), use square brackets.
- Large boats and industrial dumping affect marine life (including aquatic mammals [e.g., dolphins]).
- Climate change caused temperatures to rise (to unprecedented levels [Table 1]) throughout the twenty-first century.
In British usage, nested parentheses (round brackets within round brackets) are used instead of square brackets.
- American: Many cats like cheese (see The Complete Cat Manual [p. 231]).
- British: Many cats like cheese (see The Complete Cat Manual (p. 231)).
In British English, round brackets are called “brackets” or “round brackets” rather than “parentheses.” In U.S. English, round brackets are known as “parentheses,” with square brackets being called “brackets” or “square brackets.”
Parentheses vs. square brackets
Use square brackets when you need to show brackets within brackets. Parentheses (round brackets) are used first, with square brackets reserved for parenthetical matter in text already within parentheses.
- Global inflation rates are expected to continue increasing (based on predictive algorithms [see Figure 1]).
- Use parentheses (or [round] brackets, as they are known in British usage) to set off supplementary information from the main text.
Brackets are also used instead of parentheses to add author’s notes or clarifications to quoted text.
- The senator’s words were clear, “This matter will be resolved by tomorrow [Tuesday, August 9].”
- As Dash remarks, “There are many ways to core an apple, but only one right way [read Life on a Farm], and the right way is different for everyone.”
- The instructions say to use “inedible [sic] ink.”
Parentheses vs. commas and dashes
Parenthetical information may be enclosed in commas, dashes, or parentheses. Text enclosed in commas is more tightly integrated with the sentence.
- You cross 3,901 bridges on the Trans-Siberian Railway, the longest railroad in the world.
- The octothorpe, better known as a hash mark, is a versatile sign with many uses.
- The tour operator we hired, Nusquam Explorers, helped us plan our trip.
In contrast, text enclosed in parentheses is read separately from the rest of the passage.
- On the longest railroad in the world (the Trans-Siberian Railway), you cross 3,901 bridges.
- The longest railroad in the world (Map C, Appendix A) is the Trans-Siberian Railway.
- The octothorpe (or hash mark, pound sign, number sign) is a versatile symbol with many names.
- The local tour operator (called the Nusquam Explorers, if I remember correctly) helped us plan our trip.
Dashes (em dashes in American usage; spaced en dashes in British) function similarly but are more emphatic and dramatic than parentheses. They are also less formal.
- On the Trans-Siberian Railway—the longest railroad in the world—you cross 3,901 bridges.
- The octothorpe—more commonly known as a hash or number sign—is a versatile symbol with many names and uses.
- The company we hired—Nusquam Explorers—did a great job helping us plan our trip.
Parenthetical information is most often enclosed in commas, which are the least distracting of these punctuation marks. Avoid overusing parentheses: use them only if you want the enclosed text to be read separately from the main passage or if the parentheses are necessary for clarity.
Examples from published content
The following examples from published writing illustrate how parentheses can set off phrases, clauses, and entire sentences that provide supplementary information.
The introduction to a manuscript does not carry a heading that labels it as the introduction. (The first part of a manuscript is assumed to be the introduction.)
— Publication Manual of the American Psychological Association, Sixth Edition (2010)
Shells in the form of wampum (tubular shell beads) were used as money by Native Americans.
— “A Brief (and Fascinating
) History of Money,” Encyclopedia Britannica (Accessed August 22, 2022)
Having burned bridges with the West and sparked an energy war with Europe, Mr Putin is attempting a pivot east (he’s left himself little choice).
— “Vladimir Putin and Xi Jinping: An Increasingly Unequal Relationship,” BBC News (September 16, 2022)
As with Joyce’s Ulysses, In Search of Lost Time’s length (it’s officially the world’s longest novel) and perceived complexity mean that far more are likely to have heard of the clichés surrounding the work than have actually read it.
— Cath Pound, “Why the World’s Most Difficult Novel Is So Rewarding,” BBC Culture (August 15, 2022)
One letter to the Times, she used to say to Miss Brush, cost her more than to organise an expedition to South Africa (which she had done in the war).
— Virginia Woolf, Mrs Dalloway (1925)
Why had the king exiled him for advocating the Ekumen’s cause (which seemed to be the meaning of the proclamation) if (according to the king himself) he had been doing the opposite?
— Ursula K. Le Guin, The Left Hand of Darkness (1969)
The whole house is indeed sparsely furnished. I have introduced very little of my own. (There is only one bed; I am not expecting visitors!)... I have now had lunch (lentil soup, followed by chipolata sausages served with boiled onions and apples stewed in tea, then dried apricots and shortcake biscuits: a light Beaujolais) and I feel better.
— Iris Murdoch, The Sea, the Sea (1978)
Enclose text in parentheses to set it off from the rest of the passage. Parentheses are also used in bibliographic citations in many styles. Punctuation like periods and question marks goes within parentheses if it belongs to the parenthetical text, and outside if it belongs to the larger sentence. Use square brackets for nested brackets (brackets within parentheses [like this]).
Parenthetical information may also be set off using commas or dashes. Text enclosed in commas is more closely related to the passage, while dashes are more forceful than parentheses. Prefer to use parentheses over dashes in formal usage.