Comma Rules

Commas are the most used punctuation mark and one of the most misused. The good news is that they follow a small set of rules, and each rule comes with a known exception. This lesson covers the standard rules for formal written English: lists, introductions, joining sentences, extra information, adjectives, direct address, dates, and places. You will also learn the comma splice and the places where a comma does not belong. Commas follow grammar, so our guide will be clauses, not pauses.

Start here: clauses and phrases

Most comma rules depend on clauses, so learn these three terms first.

• An independent clause has a subject and a verb and makes a complete thought. It can stand alone as a sentence: The bus was late.
• A dependent clause has a subject and a verb too, but it begins with a word such as because, when, if, although, who or that, so it cannot stand alone: because the bus was late.
• A phrase is a group of words without its own subject-and-verb pair: after the game, on Saturday, to finish early.

Here is a quick test. Can the group of words stand alone as a complete sentence? If yes, it is an independent clause. The sentence Because the bus was late, we missed the quiz. has one dependent clause and one independent clause.

Rule 1: Items in a series (and the serial comma)

Use commas to separate three or more items in a series. Put a comma after every item except the last, including before the and or or that comes before the last item.

Right: We packed sandwiches, apples, and water.

The comma before the final and is called the serial comma (or Oxford comma). Style guides do not all agree about it. Many school and college guides, such as MLA and Chicago, use it, while newspaper style (AP) usually leaves it out. This site uses the serial comma, so every list here has it. Check which style your teacher or publication wants.

Leaving it out can change the meaning. Compare these two sentences:

• Clear: I thank my parents, the principal, and the coach. This names three separate groups of people.
• Confusing without the serial comma: I thank my parents, the principal and the coach. A reader may take this to mean that my parents are the principal and the coach.

Exceptions:

• Two items joined by and or or take no comma: We packed sandwiches and apples.
• If the items already contain commas, separate them with semicolons: The team visited Dallas, Texas; Tulsa, Oklahoma; and Denver, Colorado.

Rule 2: After an introductory word, phrase, or clause

An introductory element comes before the main clause. Put a comma after it.

• Word: Meanwhile, the band tuned up.
• Phrase: After the game, we ate pizza.
• Dependent clause: When the bell rang, the students left.

Exceptions:

• A short introductory phrase of a few words may skip the comma if the sentence is still easy to read: In May we moved. (In May, we moved. is also correct. Guides differ on how short is short, so this is a convention, and the comma is always safe.)
• When the dependent clause comes after the main clause, there is usually no comma: The students left when the bell rang. The common exception is a contrast clause beginning with although, though, even though, or whereas, which usually takes a comma: We stayed late, although we were tired.
• Do not mistake a subject for an introduction. In Walking to school is good exercise. the words Walking to school are the subject, so no comma follows them. In Walking to school, Dana saw a fox. the phrase is an opener and Dana is the subject, so the comma is needed.

Rule 3: Before a FANBOYS word that joins two independent clauses

A coordinating conjunction joins equal parts of a sentence. There are seven, and the memory trick FANBOYS gives them: For, And, Nor, But, Or, Yet, So.

Rule: when a coordinating conjunction joins two independent clauses, put a comma before it.

• Nina wanted pizza, but Omar wanted tacos.
• The test was hard, yet most students passed.
• We stayed home, for it was raining. (Here for means because.)
• She does not like spiders, nor does she like snakes. (After nor, the verb comes before the subject.)

Check: cover the conjunction. Is there a complete sentence, with its own subject and verb, on each side? If so, use the comma.

Exceptions:

• No comma when the conjunction joins only two verbs or two phrases. She opened the door and walked in. has one subject (She) doing two things. We can meet after school or on Saturday. joins two phrases.
• When both clauses are very short and closely connected, the comma may be left out: I called and he answered. Using the comma is always acceptable.

Watch for words that do other jobs. In We waited for the bus. the word for is a preposition, and in I am so tired. the word so is an adverb. No comma goes in either sentence.

Rule 4: Nonessential and essential clauses and appositives

Some groups of words add extra information. Others are needed to tell which person or thing you mean.

• A nonessential (or nonrestrictive) clause or appositive can be removed without changing who or what the sentence is about. Set it off with commas.
• An essential (or restrictive) clause or appositive is needed to identify the noun. Use no commas.

An appositive is a noun or noun phrase that renames the noun beside it.

The test: cross the words out. Does the sentence still point to the same person or thing? If yes, the words are nonessential, so add commas. If the sentence becomes unclear or its meaning changes, the words are essential, so use no commas.

• My brother, who lives in Ohio, plays the cello. The commas tell the reader that where he lives is extra. This is the natural way to write it if I have one brother.
• My brother who lives in Ohio plays the cello. With no commas, the clause tells which brother, so this suggests that I have more than one.
• The student who finished first won a medal. Without the clause, we would not know which student, so it is essential.
• Our principal, Ms. Alvarez, spoke first. A school has one principal, so the name is extra.
• My cousin Priya plays the violin. No commas: I have several cousins, and the name tells which one.

Commas come in pairs. When the extra information is in the middle of a sentence, put one comma before it and one after it. When it comes at the end, one comma before it is enough: We met Ms. Alvarez, who teaches chemistry.

WRONG: My brother, who lives in Ohio plays the cello. (The second comma is missing.)

That or which? In standard American formal writing, use that for essential clauses (no commas) and which for nonessential clauses (with commas). The book that I borrowed was long. The book, which I borrowed from the library, was long. The word who can begin either kind when you are talking about people. Never put a comma before an essential that clause. (Many usage guides, and British English, accept which in essential clauses too, but the that/which split is the safe choice in American school writing. That never begins a nonessential clause.)

Rule 5: Coordinate adjectives

Coordinate adjectives each describe the noun on their own. Put a comma between them. Use two quick tests:

1. Can you put and between them?
2. Can you swap their order?

If the tests work, the adjectives are coordinate: a cold, windy day (a cold and windy day, or a windy, cold day). If the tests disagree, trust the and test. With three, the pattern continues: a cold, windy, rainy day.

Exception: cumulative adjectives build on each other in a set order, and both tests fail. Use no comma: four old maps (not old four maps), a worn leather wallet (not a leather worn wallet).

Never put a comma between the last adjective and the noun. WRONG: a cold, windy, day.

Rule 6: Direct address, dates, and places

• Direct address. Set off the name or title of the person you are speaking to: Maya, please close the door. Please close the door, Maya. I think, Maya, that you are right. Exception: use no commas when the name is only part of the sentence and nobody is being addressed: Maya closed the door.
• Dates. In month-day-year order, put a comma between the day and the year, and another after the year when the date sits inside a sentence: Our concert is on May 12, 2027, at the high school. Exceptions: a month and a year alone take no comma (in May 2027), and neither does the day-month-year order (on 12 May 2027).
• Places and addresses. Put a comma between a city and a state, and another after the state when the sentence continues: She lives in Portland, Oregon, and works downtown. Exceptions: no comma goes between a state and a ZIP code, or between a street number and the street name: 123 Maple Street, Ridgeview, OH 44444.

Where no comma goes

Here is a short list of places where a comma does not belong, each with its exception.

1. Between a subject and its verb. The students in the back row fell asleep. Even a long subject gets no comma before its verb. Exception: a pair of commas can wrap extra information that interrupts, as in The students, who were tired, fell asleep. A single comma never splits the subject from the verb.
2. Between two verbs or two phrases joined by a conjunction. See Rule 3. Exception: three or more items form a series (Rule 1).
3. Between the last adjective and its noun, or between cumulative adjectives. See Rule 5.
4. Right after a conjunction that begins a sentence. But the game went on. Many style guides accept starting a sentence with And or But in formal writing (check your teacher's preference), and no comma follows it. Exception: extra information right after the conjunction still gets its own pair of commas: But, as it turned out, the game went on.
5. Usually before a dependent clause that follows the main clause. The students left when the bell rang. Exception: a contrast clause with although usually takes a comma. See Rule 2.
6. Where the date and address rules say none: between a month and a year, between a state and a ZIP code, and between a street number and a street name.

A rule of thumb that fails: many people learn to put a comma wherever they pause when reading aloud. That is unreliable. You may pause after a long subject, where no comma belongs, and you hardly pause in Dallas, Texas, where one does. Decide by the grammar, not by your breath.

Rule 7: The comma splice and three fixes

A comma splice joins two independent clauses with only a comma. In standard written English it is an error, because a comma alone is too weak to join two complete sentences.

WRONG: The bus was late, we missed the quiz.

Three fixes:

1. Period. Make two sentences: The bus was late. We missed the quiz.
2. Semicolon. Join the closely related clauses: The bus was late; we missed the quiz.
3. Comma plus a FANBOYS conjunction. The bus was late, so we missed the quiz.

Sneaky splices. Words such as however, therefore, then, also, and instead are not coordinating conjunctions. They are called conjunctive adverbs. When one of them starts the second of two independent clauses, a comma before it still makes a splice.

WRONG: It was late, however, we kept playing.

Right: It was late; however, we kept playing. (a semicolon before however and a comma after it)

Exceptions and cousins:

• If one of the two clauses is dependent, there is no splice. A bonus fix is to make one clause dependent: Because the bus was late, we missed the quiz.
• A series of three or more short, parallel clauses may be separated by commas, with and before the last one: We laughed, we cried, and we cheered.
• Two independent clauses with no punctuation at all form a fused (run-on) sentence. The same three fixes work.
• When however or therefore only interrupts one clause, it is not joining anything, so a pair of commas is correct: The plan, however, worked.