The comma has a reputation for being mysterious, partly because style guides disagree on the details. In everyday writing, though, a handful of rules cover most situations. Here are five, with examples.
1. After an introductory phrase
When a sentence opens with a word or phrase that sets the scene, add a comma before the main clause.
- “After the meeting, we sent the notes.”
- “However, the plan changed.”
- “When the draft is ready, send it to me.”
With very short openers the comma is sometimes optional (“Yesterday we met”), but using it consistently is a safe choice.
2. Between items in a list
Use commas to separate three or more items: “We tested the headline, the opening and the call to action.”
Whether to use a comma before “and” in the list, known as the serial or Oxford comma, depends on the style guide. Many American guides favour it, while some British and journalistic styles leave it out. Whichever you pick, use it consistently. It can prevent ambiguity: “I thank my parents, Alex and Sam” can read differently from “I thank my parents, Alex, and Sam.”
3. Before a conjunction that joins two full sentences
When “and,” “but,” “or,” “so” or “yet” joins two independent clauses, put a comma before it.
- “The draft was finished, but the images were missing.”
- “We can publish today, or we can wait for the final review.”
If the second part is not a full sentence, you generally do not need the comma: “The draft was finished but incomplete.”
4. Around extra information
Commas can set off a phrase that adds detail but is not essential to the sentence’s meaning. If you can remove it and the sentence still works, use a comma on each side.
- “My editor, who lives in Leeds, reads every draft.”
- “The report, published in March, drew little attention.”
When the phrase is needed to identify what you mean, do not use commas: “The writers who missed the deadline were contacted.” Here “who missed the deadline” tells us which writers.
5. Between adjectives that work separately
When two adjectives each describe the noun independently, separate them with a comma: “a clear, concise summary.” A quick test is to swap them or insert “and.” If “a concise and clear summary” still sounds right, you need the comma. In phrases like “a large wooden desk,” the adjectives are stacked in a natural order and take no comma.
One mistake worth avoiding
Do not put a single comma between a subject and its verb. “The writers who stayed late, finished the draft” is wrong, because the comma splits the subject from what it does. If you add a pair of commas around extra information, as in rule four, that is fine.
A related problem: the comma splice
A comma splice joins two full sentences with only a comma: “The draft is ready, we can publish.” Fix it with a full stop, a semicolon or a conjunction: “The draft is ready, so we can publish.”
Using these rules
You do not need to memorise every exception. Learn these five, read your sentences aloud, and notice where you naturally pause. Most of the time, commas follow the rhythm of speech, and the rules above explain why.
