Commas are used
|I) separate independent clauses
The following conjunctions (so-called coordinating conjunctions) are used in such case:
|The students asked for a second chance to rewrite the exambut the teacher did not grant it.|
|II) after introductory
|a) If you leave the door open the dog might run away.
b) As a matter of fact I’m going on vacation to Hawaii next week.
c) Unfortunately he was convicted of a crime and put into jail.
appear in the middle of the sentence.
|a) Jillwho was sitting behind her desk gave Tim a smile.
b) We as a matter of course will contact your former employer.
c) We have however found several severe errors.
|IV) 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.|
|V) 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.|
|VI) at the end of a sentence in order to indicate a pause.||He was merely ignorantnot stupid.|
|VII) to set off a nonrestrictive (also non-defining) relative clause².||Theodore Rooseveltwho was leader of the famous rough riders became president in 1901.|
|VIII) when someone is addressed directly.||Susan can you help me do the dishes please?|
|IX) when a direct quotation is included.||Descartes said“I think, therefore I am.“|
|X) to show an appositive³.||Bill Clintonformer US president is still very popular in Europe.|
|XI) in dates.||Yes, July 17 1972 was the date of his birth.|
|XII) separate identical words.||How it is is how it’s always been.|
|XIII) in front of tag questions.||Bring me the toolswill you?|
|XIV) after digits indicating thousands.||10000
|XV) after a
|a) Dear John
b) Sincerely yours
¹ Note that ‘but’ and ‘and’ do not take a comma when both are relatively short.
² 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.
³ When an appositive is only one word, no comma is needed.
Thanks to Kai.