Some commas follow custom more than meaning. You will use them in every letter and email: in dates, between a city and its state, after yes and no, before a short tag question, and around the name of someone you are speaking to (direct address). They build on commas in a series.
- Dates: “On May 4, 2025, the library opened.” A month and year alone take no comma: “in May 2025.”
- Places: “We drove from Akron, Ohio, to Erie.”
- Yes and no: “Yes, I can come.” “No, thank you.”
- Tag questions: “It’s cold today, isn’t it?”
- Direct address: “Thanks, Sam.” “Sam, can you help?” “I think, Sam, that you’re right.”
Key idea
Use a comma between the day and the year and between a city and its state. When the date or place sits in the middle of a sentence, put a comma after the year or state too. Set off yes, no, tag questions and the name of the person you are speaking to.
Why it works
These commas keep numbers and names from running together (“July 4 1776”) and show who is being spoken to. The old joke says it best: “Let’s eat, Grandma!” invites Grandma to dinner. “Let’s eat Grandma!” is a very different plan.
Worked example: A place in the middle of a sentence
Add commas: “We moved to Boise Idaho in June.”
- Boise is the city and Idaho is the state: comma between them.
- The sentence keeps going after Idaho, so the state gets a comma after it too.
Answer: We moved to Boise, Idaho, in June.
Worked example: Yes and a name
Add commas: “Yes Ms. Park I finished the book.”
- Yes starts the sentence: comma after it.
- Ms. Park is the person spoken to, in the middle: commas on both sides.
Answer: Yes, Ms. Park, I finished the book.
Common mistake
Forgetting the second comma: “On May 4, 2025 the library opened.” A year or a state in the middle of a sentence is closed off on both sides, like a pair of brackets. The other common slip is leaving out the comma of direct address, which can change the meaning.