Punctuation shows your reader where one idea ends and the next begins. This lesson covers the marks that cause the most trouble in American emails and reports.
The pattern
When the rain stops, we'll walk home.
The rent is high, but the location is perfect.
We need three things: plates, cups, and ice.
01Commas in lists
Put a comma between the items in a list of three or more. Most American style guides for books and college writing also put a comma before the final and or or. This is the serial comma, also called the Oxford comma. News writing often leaves it out, so both styles are accepted. This lesson uses it. Just be consistent.
- I bought eggs, spinach, and coffee.
- You can pay by card, cash, or check.
02Commas after openers and before and, but, so
Use a comma after an opening clause or word such as When, If, Because, After, However, or Unfortunately. When the if or because clause comes second, you usually don't need a comma.
When and, but, so, or, or yet joins two full sentences (each with its own subject and verb), put a comma before it. If the second part has no subject of its own, don't use a comma.
- If you're running late, text me.
- Text me if you're running late.
- The meeting ran long, so I missed my bus.
- I finished the report and sent it to my manager.
03No comma splices
A comma alone can't join two full sentences. That mistake is called a comma splice. Fix it with a period, a semicolon, or a comma plus and, but, or so. However and therefore can't join two sentences with a comma either. Put a period or a semicolon before them.
| Comma splice (wrong) | Fixed |
|---|---|
| My phone died, I couldn't call. | My phone died. I couldn't call. |
| The price is good, however it's far. | The price is good. However, it's far. |
04Apostrophes: owners, not plurals
Add 's when one person or thing owns something: my boss's office, Sam's car. For a plural that already ends in s, add only an apostrophe: my parents' house, the nurses' lounge. Irregular plurals take 's: the children's books, the men's room.
Never use an apostrophe for a plain plural: two coffees, the 1990s, the Garcias. And remember that its (belonging to it) has no apostrophe, while it's means it is or it has.
| Meaning | Write it |
|---|---|
| one owner | my sister's apartment |
| plural owners | my sisters' apartment |
| plain plural | three apartments |
| it is / it has | it's cold |
| belonging to it | its roof |
05Colons and quotation marks
Use a colon after a complete sentence to introduce a list or an explanation. Don't put one right after a verb like are or include, or after such as.
In American English, periods and commas always go inside closing quotation marks. Question marks go inside only when the quote itself is a question. British English often puts the period outside.
- "I'll call you tonight," she said.
- Did she really say "no problem"?
06Common mistakes
The flight was canceled, we stayed at a hotel.
The flight was canceled, so we stayed at a hotel.
A comma alone can't join two full sentences.
We sell fresh bagel's every morning.
We sell fresh bagels every morning.
Plain plurals never take an apostrophe.
Please bring: a towel, sunscreen, and water.
Please bring three things: a towel, sunscreen, and water.
A colon needs a complete sentence before it.
She said, "See you soon".
She said, "See you soon."
American English puts periods inside quotation marks.