The comma is one of the trickiest punctuation marks, largely because it serves many different functions. Sometimes it represents a pause in speech, while other times it separates different parts of a sentence. Additionally, commas are often used in specific situations simply due to conventional rules.
A missing or misplaced comma can dramatically change the meaning of a sentence. In some cases, it can even make a sentence convey the opposite of what was intended. Therefore, it’s important to use commas carefully.
Conventional Uses of the Comma
These common rules apply to using commas in various mechanical ways. Once learned, they are easy to apply.
Numbers
When writing large numbers, place a comma after every third digit from the right, except for years, page numbers, and addresses.
Correct:
- We sold 2,345 cookies during the fundraiser.
- She lives at 1234 Elm Street.
Incorrect:
- We sold 2345 cookies during the fundraiser.
- She lives at 1,234 Elm Street.
Jr. and Inc.
No comma is required before “Jr.” or “Inc.” in a name.
Correct:
- Charles Brown Jr. is an accomplished artist.
- She works for TechWorld Inc.
Incorrect:
- Charles Brown, Jr. is an accomplished artist.
- She works for TechWorld, Inc.
Degrees and Certifications
Commas should separate a degree or certification from the person’s name.
Correct:
- The report was written by John Adams, MD.
- Sarah Lee, CPA, will audit our accounts.
Incorrect:
- The report was written by John Adams MD.
- Sarah Lee CPA will audit our accounts.
Direct Address
When addressing someone directly, use a comma to separate their name or title from the sentence.
Correct:
- Thank you, Sarah, for your help.
- Could you clarify this point, Professor?
Incorrect:
- Thank you Sarah for your help.
- Could you clarify this point Professor?
Dates
When writing the day, month, and year, place a comma between the day and year. If the date appears mid-sentence, add a comma after the year.
Correct:
- We met on January 5, 2022, in the city.
- Her birthday is April 3, 1990.
Incorrect:
- We met on January 5 2022 in the city.
- Her birthday is April 3 1990.
When the date includes only the month and year, no comma is required.
Correct:
- The company was founded in June 1998.
Incorrect:
- The company was founded in June, 1998.
Geographic References
Use commas to separate parts of geographic locations.
Correct:
- They moved to Portland, Oregon, last year.
- Our headquarters is located in Tokyo, Japan.
Incorrect:
- They moved to Portland Oregon last year.
- Our headquarters is located in Tokyo Japan.
Listing Comma (Oxford Comma)
In a list of three or more items, commas are used to separate each item. Including a comma before the last item (the Oxford comma) is optional but can avoid confusion.
Correct:
- We bought apples, bananas, and oranges.
- The winners were Jane, Alice, and Sarah.
Incorrect:
- We bought apples, bananas and oranges.
- The winners were Jane, Alice and Sarah.
Multiple Adjectives
If multiple adjectives independently modify a noun, use commas to separate them. If the adjectives work together to describe the noun, no comma is needed.
Correct:
- She wore a bright, colorful scarf.
(Each adjective describes the scarf separately.) - He held a large red balloon.
(“Large red” describes one type of balloon.)
Incorrect:
- She wore a bright colorful scarf.
- He held a large, red balloon.
Nonessential Information
Use commas to set off nonessential information, which provides extra details but isn’t crucial to the sentence’s meaning.
Correct:
- My sister, Emily, is moving to New York.
(I have only one sister; her name is nonessential.) - The house, built in 1900, needs major repairs.
Incorrect:
- My sister Emily is moving to New York.
(I have more than one sister, so her name is essential.) - The house built in 1900 needs major repairs.
Introductory Phrases
A comma is typically used after an introductory word or phrase to separate it from the rest of the sentence.
Correct:
- After the meeting, we went for lunch.
- Yes, I will attend the conference.
Incorrect:
- After the meeting we went for lunch.
- Yes I will attend the conference.
Afterthoughts
When adding a final thought or phrase at the end of a sentence, use a comma to separate it.
Correct:
- I’ll call you later, okay?
- She won the race, by the way.
Incorrect:
- I’ll call you later okay?
- She won the race by the way.