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Every comma decision

Does this spot need a comma? The four jobs a comma does, and the places it never goes.

Don't place a comma by where you'd pause out loud; readers pause in different places. Instead, ask what job the comma would be doing. Joining two complete sentences with a FANBOYS word? Comma before the FANBOYS word. Setting off something the sentence could lose: an opening phrase or clause, an interrupter, an appositive, a nonessential which or who clause, a name you're speaking to? Commas around it (one comma if it's at the start or end). Separating the items in a list, or the parts of a date, address, or quotation? Use the list or format rule. If none of these jobs applies, leave the comma out, and check the never-list: no comma between a subject and its verb, before a FANBOYS word joining only words or phrases, or around a clause the sentence needs.

Joining two complete sentences

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The comma placed before a coordinating conjunction linking two independent clauses.

Example

The store closed early, but the pharmacy stayed open.

Only with a FANBOYS word after it; run the period test on both halves first.

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Two or more verbs sharing one subject, joined by a conjunction.

Example

The store closed early and reopened at six.

The look-alike that takes no comma, one subject doing two things.

Setting off extra information

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The comma (or comma pair) marking the boundary of something nonessential to the sentence's core meaning.

Example

After lunch, the team met. / The plan, however, changed.

Opening elements, interrupters, and direct address all get fenced off.

Term

appositive

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A noun phrase placed right beside another noun to rename it.

Example

Ms. Ruiz, our coach, called the meeting.
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A clause that adds extra information without changing which thing is meant, and so is set off with commas.

Example

My sister, who lives in Denver, visits every summer.

Commas around a which/who clause the sentence could lose.

Lists and formats

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The comma before the conjunction in a list of three or more items.

Example

We packed tents, stoves, and maps.

Where a comma never goes

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A clause that identifies which specific thing is meant, and so is never set off with commas.

Example

Students who finish early may leave.

A clause the sentence needs to identify its noun takes no commas.