Commas vs. Parentheses vs. Dashes

Summary

Commas, parentheses, and dashes can all be used to enclose additional information. Use commas to clarify your main idea and integrate a description into the flow of your sentence. Use parentheses to present supplementary information or an afterthought and set it off from the surrounding text. Use dashes to make information stand out. Dashes are less formal and more emphatic and dramatic than commas and parentheses.

Parenthetical punctuation

Commas, parentheses, and dashes can all be used to enclose parenthetical or optional information in a sentence. Such information is essential neither to the meaning nor to the grammar of a sentence, which means that the sentence would read perfectly fine if you removed this information.

Examples
  • The two interns, Maya and Anita, are working on the project.
  • The two interns (Maya and Anita) are working on the project.
  • The two interns—Maya and Anita—are working on the project.
  • We ordered from the new Thai place, the one at the pier.
  • We ordered from the new Thai place (the one at the pier).
  • We ordered from the new Thai place—the one at the pier.

Although parenthetical information is not essential, it can still be useful or interesting to the reader. Depending on the relevance of the information being provided, it can be set off using commas, parentheses (round brackets), or em dashes.

Commas vs. parentheses

Use commas when you want to integrate additional information into the flow of your sentence. Use parentheses instead if you want to set off supplementary information from the rest of the text, making it less important. Commas are used to describe and clarify the main idea of the sentence. Parentheses generally mark an afterthought or other optional text—information added later to a sentence.

Examples
  • Order our new range of towels, now on sale.
  • Class is on Monday, 2 to 4 p.m.
  • Order our new range of towels (made of pure Egyptian cotton).
  • Class in on Monday (2 to 4 p.m. as usual).

Integration vs. separation

While commas integrate information into the flow of your sentence, parentheses separate and subordinate it. Commas are more commonly used and less disruptive to the flow of a sentence than parentheses.

Examples
  • My sister, Anita, is a doctor.
    My sister’s name is Anita. While this information is not essential to meaning, we’ve used commas instead of parentheses so that it stays in the flow of the sentence.
  • My sister, Anita, is a doctor (an oncologist).
    The fact that she is an oncologist is an afterthought, information added later and read separately from the rest of the sentence.
  • My sister, who works at Nusquam General, is an oncologist.
    Commas enclose optional information that is part of the flow of the sentence.
  • My sister (the one who works at Nusquam General) is an oncologist.
    Parentheses enclose supplementary information and set it off from the rest of the sentence.
Caution

Commas are the default punctuation to present optional information and should be your first choice. Parentheses separate information from the rest of the sentence and should be used sparingly. Enclosing too much text in parentheses can affect the coherence and flow of your writing and make a passage look disjointed and messy.

Examples
  • Poor: My sister (Maya) is a doctor (an oncologist) who works at Nusquam General (a large hospital in the city).
  • Better: My sister, Maya, is an oncologist who works at Nusquam General, a large hospital in the city.
  • Also acceptable: My sister, Maya, is a doctor (an oncologist) who works at Nusquam General, a large hospital in the city.

Parentheses for clarity

Parentheses may be used to set off a phrase that already contains commas. Using parentheses instead of commas to enclose such a phrase can improve readability.

Examples
  • The first meteor hit on a Monday (June 6, 2022) just before rush hour.
  • Cetaceans (whales, dolphins, and porpoises) are a group of marine mammals.

Around abbreviations and definitions

Both parentheses and commas can be used to introduce an abbreviation or provide a definition. As usual, information enclosed in commas is read with the flow of the sentence, while parentheses set it off from the rest of the text.

Examples
  • Correct: The National Aeronautics and Space Administration, or NASA, is the U.S. government agency responsible for space research.
  • Correct: Monotremes, which are egg-laying mammals, are found in Australia and Papua New Guinea.
  • or
  • Correct: The National Aeronautics and Space Administration (NASA) is the U.S. government agency responsible for space research.
  • Correct: Monotremes (egg-laying mammals) are found in Australia and Papua New Guinea.

Commas and parentheses vs. dashes

Use em dashes instead of commas and parentheses if you want to make information stand out. Commas allow for a smoother read than dashes, which interrupt the sentence to draw the reader’s attention. Parentheses diminish the importance of a phrase, while dashes enhance it.

Examples
  • A local travel agent, Nusquam Nation, helped arrange our tickets.
  • We hired a local travel agent (Nusquam Nation) to help with tickets and accommodation.
  • The travel agent we hired—Nusquam Nation—did an excellent job with our bookings.

All three punctuation marks—commas, parentheses, and dashes—can present the same information: which punctuation you use depends on how integrated you want the information to be with the rest of the sentence and how much attention you want to draw to it.

Considerations of formality

Commas and parentheses, which are quieter, are preferred in formal texts (such as academic and business writing), although they are also frequently used in informal writing. Em dashes, which are more emphatic and dramatic, are seen mainly in informal and creative writing.

Examples
  • More formal: The eel, a fish with a mysterious life cycle, goes through five distinct stages until it reaches maturity.
    Less formal: The eel—a fish with a mysterious life cycle—goes through five distinct stages until it reaches maturity.
  • More formal: The eel (a type of bony fish) has a mysterious and complex life cycle.
    Less formal: The eel—a bony fish and not a reptile as many assume—has a mysterious and complex life cycle.
Caution

Unless at the end of a sentence, dashes, like parentheses, come in pairs. Don’t forget to use a dash both before and after the parenthetical phrase.

Example
  • Incorrect: Xenarthransanteaters, tree sloths, and armadillos, are an ancient lineage of mammals found in the Americas.
    Correct: Xenarthransanteaters, tree sloths, and armadillosare an ancient lineage of mammals found in the Americas.

Dashes for clarity

Like parentheses, dashes may be used instead of commas to set off a phrase that contains internal commas. Using dashes instead of commas can then improve clarity and help avoid confusion.

Examples
  • On that day—July 1, 2000—my life changed.
  • Pinnipeds—seals, sea lions, and walruses—are a group of marine mammals.

To mark an interruption or aside

Dashes can also mark an interruption or an aside. Commas cannot be used in this way. Parentheses can mark an interruption, but dashes make the idea stand out, while parentheses subordinate it.

Example
  • Incorrect: The cat, or was it a ghost?, broke the vase.
    Correct: The cat—or was it a ghost?—broke the vase.
    Also correct: The cat (or was it a ghost?) broke the vase.
Tip

In British usage, a spaced en dash is generally used instead of the em dash.

Examples
  • British: The cat’s purr – a sound a cat makes when it is happy and content – can help humans destress and relax.
  • American: The cat’s purr—a sound a cat makes when it is happy and content—can help humans destress and relax.

Em dash instead of colon

An em dash can also replace a colon in a sentence to introduce new information that explains or builds upon what precedes it. Parentheses and commas cannot be used in this way. (The colon is quieter and preferred in formal usage; the dash is louder and more dramatic.)

Example

Quick Quiz

Which of these reads the most smoothly?
Choose from these answers
All done!
Which of these indicates that information provided is supplementary, like an afterthought?
Choose from these answers
All done!
In which of these is additional information provided in a dramatic fashion to make it stand out?
Choose from these answers
All done!
Which of these sentences is/are more acceptable in formal writing?
Choose from these answers
All done!

Did You Know?

Brackets instead of parentheses enclose an editorial comment or correction.
Know more:Square Brackets [ ] in English: How to Use Correctly