Trouble with commas? 17 comma rules, with examples

Commas separate the parts of a sentence so that its meaning is clear. This article sums up the comma rules of English: first the main dos and don'ts, then 17 rules with examples, from lists and clauses to dates and numbers.

Commas are small, and they are easily overlooked when inspiration strikes, but they are important. And tricky. Punctuation marks such as commas, periods, and semicolons can drive you mad when you check a text, because you never feel quite sure about the rules. And, to be honest, who cares about comma rules in daily life?

Punctuation errors matter in two cases: when they change the meaning of a sentence or lead to misunderstandings, and when they slip through because nobody notices them while proofreading.

What do the rules say about commas?

Who decided on these rules is another question, and one without a definite answer (see who decides what is right or wrong in English grammar). This article sticks to what standard grammar references say.

A popular guide such as GrammarBook.com lists rule after rule. English has a reputation as a pragmatic language, but its comma rules can be as detailed and pedantic as those of German, a language famous for its complex rules.

To make things more complicated, there are rules about what you should do and rules about what you should not do, and some rules have their own dos and don'ts.

Do

• Use a pair of commas around a non-defining clause. It adds descriptive information that can be removed without changing the meaning of the sentence, and only who or which can start it: My brother, who lives in Leeds, is visiting.
• Use commas around a non-defining word or phrase, which adds information but could be left out: The report, as you know, is late. Use a single comma if the phrase starts the sentence: As you know, the report is late.
• Use a comma after an introductory adverb, adverbial phrase, or subordinate clause, or a pair of commas around it in the middle of a sentence: Unfortunately, the train was late. The train was, unfortunately, late.
• Use a comma between qualitative adjectives, the ones you can compare or modify with very or quite: a long, boring meeting.
• Use a comma between the items in a list: apples, pears, and plums. Some style guides leave out the comma before the final and or or unless it prevents ambiguity. That comma is called the Oxford comma.

Don't

• Do not put commas around a defining clause, which starts with that, which, or who and cannot be removed without changing the meaning: The car that hit me was red.
• Do not put commas around a defining word or phrase that tells you which one is meant: The poet Keats died young.
• Do not join two main clauses with a comma alone, and not with a comma and a linking adverb such as nevertheless or therefore. That mistake is a comma splice. Use a semicolon, or add a coordinating conjunction such as and, but, or so: It was late; therefore, we left.
• You do not need a comma after a short phrase of time at the start of a sentence: Last week we visited Paris.
• Do not use a comma between classifying adjectives, which either apply or do not, such as French, wooden, or medical: a French medical student.
• Do not use a comma between a qualitative and a classifying adjective: a beautiful Italian villa.

Keep the spirit of the rules

It would be madness to recall every rule consciously while you write. Most writers know the rules by instinct: they write the first draft in a creative rush, then step back and take a look, or run a checker over the text and correct whatever comes up.

It makes sense to keep the spirit of the rules in mind: a sentence must be clear in what it means and what it refers to. That simple principle makes things easier. Some commas are vital for the meaning of a sentence, and others are optional. Let's eat, Grandma is an invitation; Let's eat Grandma is something else entirely.

17 comma rules for those with a good memory

For everyone who likes rules and has a good memory, here are 17 basic rules to keep in mind.

1. Use a comma before and, but, or, so, or yet when it joins two main clauses: I called her, but she did not answer. Some writers leave it out when the clauses are short. Without such a word, a comma alone is not enough.
2. Put a comma after a subordinate clause that comes before the main clause: When it rains, we stay inside. When the main clause comes first, you usually need no comma: We stay inside when it rains.
3. In a sentence that starts with an if clause, the comma separates the condition from the consequence: If you hurry, you will catch the bus.
4. A comma introduces direct speech when the speaker is named first: She said, "I'm tired." When the speaker comes after the quotation, the comma goes before the closing quotation mark: "I'm tired," she said. If the quotation ends with a question mark or an exclamation point, add no comma: "Are you tired?" she asked.
5. Put commas around words that are not part of the main sentence, and around relative clauses with who or which that are not vital for the meaning, as described above.
6. Use a comma after an introductory infinitive, prepositional, or participle phrase: To win the race, you must train. After the long meeting, we went home. Smiling, she opened the door.
7. Separate two or more adjectives of equal rank with a comma: a cold, dark night.
8. Use a comma before a contrast introduced by not: It was the dog, not the cat, that barked.
9. Use a comma after an adverb such as however, therefore, or fortunately at the start of a sentence. After so, then, and yet, it is optional.
10. Separate the items of a list with commas. The comma before the final and is optional in some styles, but it helps when an item already contains and: I ordered soup, fish and chips, and a lemonade.
11. In English, commas separate the thousands in numbers, and a period marks the decimals: $10,000,000, but $9.99. For more, read the rules for writing numbers.
12. In an American-style date, a comma separates the day from the year: May 6, 2014, but May 2014. In British style, write 6 May 2014 without a comma.
13. Use a comma to set off the name of the person you speak to: Anna, come here. Thank you, Mr. Smith. After the greeting of a letter or an email, a comma is common: Dear Anna,
14. Separate the parts of a place name with a comma: Dublin, Ireland or Boise, Idaho.
15. Addresses need a comma between each element: 32nd Street, Manhattan, New York.
16. Put a comma before a polite please at the end of a sentence: Close the door, please.
17. Put a comma after yes or no at the start of an answer, and before a question tag: No, I don't want to. You'll never understand this, will you?

Let an app do the remembering

If that is too much to keep in your head, you are not alone. The Spell Checker checks punctuation as well as spelling and grammar, underlines each issue, and explains it. For more practice, read about correct comma usage and the important rules for comma usage.