Commas

Form

A comma marks a short break that keeps the parts of a sentence clear, and four patterns cover most of its work.

It separates three or more items in a list (flour, eggs, and butter) and usually follows an opening clause or a longer opening phrase (After dinner, we watched a movie). It goes before and, but, or or so when the word joins two complete sentences (I called her, but she did not answer). And a pair of commas fences off information the sentence does not need in order to say which thing it means (My manager, who joined in January, has changed everything).

When to Use It

1. 1

   Separating three or more items in a list

   We need flour, eggs, and butter.

2. 2

   After an opening clause or a longer opening phrase

   Although it was raining, we went for a walk.

3. 3

   Before and, but, or or so joining two complete sentences

   I called my friend, and she did not answer.

4. 4

   Around information the sentence could drop

   My only brother, who lives in Denver, is visiting next week.

5. 5

   Around an interrupter such as however or of course

   The presentation, however, was not convincing.

6. 6

   After the name of the person you are speaking to

   Marco, please close the window.

Common Mistakes

• A comma splice: write The deadline passed, and the project was unfinished, not The deadline passed, the project was unfinished — a comma on its own cannot join two complete sentences.
• A comma between a subject and its verb: write The new policy is unfair, not The new policy, is unfair — a single comma should never cut a subject off from its verb.
• A comma straight after although or because: write Although he tried his best, he could not fix it, not Although, he tried his best, he could not fix it — the comma goes after the whole opening clause, not right after although.
• Commas around essential information: write Employees who arrive late will be docked pay, not Employees, who arrive late, will be docked pay — the commas would claim that every employee arrives late.
• A comma in front of that: write The report that was published last week caused controversy, not The report, that was published last week, caused controversy — a that-clause normally gives essential information, so it takes no commas.