|The comma is used to mark off words in apposition:
||Mr Brown, our new teacher, has a red car.
|Commas are used to mark off the nominative of address:
||John, what are you doing?
|...to mark off absolute phrases:
||The day being fine, we went for a picnic.
The shops having closed, we went home.
|...to mark off adverbs and adverbial phrases that are used absolutely:
||John, however, could not come.
In conclusion, I feel that much more can be done.
|...to mark off adverbial clauses that precede the words they modify:
||Whenever I have enough time, I clean my car.
|...to separate similar parts of speech:
||My brother seems to be always reading long, dull, complicated books.
|...to mark off parenthetical clauses that interrupt the thought of a sentence:
||There was no cause, the report stated, for anyone to be unemployed.
|...to mark off non-defining adjectival clauses:
||I lost my copy of "To Kill a Mockingbird", which my father bought for me last week.
|...to mark off phrases that precede the words they qualify or modify:
||Returning home after the pictures, I met two of my friends.
|...to separate complete principal clauses, unless the clauses are very short or have the same subject:
||I shall go in Tom's car, and you will go in Peter's.
Tom stood up and walked out of the room.
I sang and Peter played the piano.
|...to separate short principal clauses that are not joined by conjunctions:
||I came, I saw, I conquered.
He entered the room, looked round at everyone, noticed me, and walked towards me.
|...to indicate parenthesis:
||The author of this book believes, and I agree with him, that most people today do not derive enough satisfaction from their work.
|...to mark off clauses that break into direct speech:
||"Our country," he said, "has unlimited resources."
|...before which introducing a principal clause
||He trains for two hours every day, which means that he rarely has time to go out.