Commas in English, Punctuation

When do we use commas?

Explanation	Examples
1. separate independent clauses The following conjunctions (so-called coordinating conjunctions) are used in such case: * and, but, for, nor, or, so, yet	The students asked for a second chance to rewrite the exam, but the teacher did not grant it.
2.1. after introductory subclauses	If you leave the door open, the dog might run away.
2.2. after introductory phrases	As a matter of fact, I’m going on vacation to Hawaii next week.
2.3. after introductory words	Unfortunately, he was convicted of a crime and put into jail.
3.1. when subclauses appear in the middle of the sentence.	Jill, who was sitting behind her desk, gave Tim a smile.
3.2. when phrases appear in the middle of the sentence.	We, as a matter of course, will contact your former employer.
3.3. when words appear in the middle of the sentence.	We have, however, found several severe errors.
4. to set off three or more words, phrases or mainclauses in a serious.	She went into the living room, sat down, and played chess on the computer.
5. to set off two or more coordinate adjectives, that is, the meaning does not change when the order is altered.	We had to travel over several narrow, winding, treacherous roads.
6. at the end of a sentence in order to indicate a pause.	He was merely ignorant, not stupid.
7. to set off a nonrestrictive (also non-defining) relative clause. **	Theodore Roosevelt, who was leader of the famous rough riders, became president in 1901.
8. when someone is addressed directly.	Susan, can you help me do the dishes please?
9. when a direct quotation is included.	Descartes said,“I think, therefore I am.”
10. to show an appositive. ***	Bill Clinton, former US president, is still very popular in Europe.
11. in dates.	Yes, July 17, 1972, was the date of his birth.
12. separate identical words.	How it is, is how it’s always been.
13. in front of tag questions.	Bring me the tools, will you?
14. after digits indicating thousands.	10,000
	9,999,999
15.1. after a salutation in letters.	Dear John,
15.2. after a farewell in letters.	Sincerely yours,

• * Note that ‘but’ and ‘and’ do not take a comma when both are relatively short.
• ** restrictive relative clause= they tell us which person or thing, or which kind of person or thing, is meant;
  non-restrictive relative clause = they tell us more about a person or thing that is already identified.
• *** When an appositive is only one word, no comma is needed.

Thanks to Kai.

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