Writing - Comma 5

The boat, which she bought five years ago, is modern and spacious.
We use a comma to separate non-defining relative clauses from the main clause. A non-defining relative clause describes a preceding noun by adding extra information about it.
Common Errors:
His new motorbike which he paid several thousand pounds is not running well. X commas required!
His new motorbike, which he paid several thousand pounds, is not running well. V two commas between extra information

He doesn't earn much money in spite of working very hard.
We don't usually put a comma after the main clause when a dependent (subordinate) clause follows it! Other subordinate conjunctions:
after, although, as, because, before, even if, even though, if, in order that, once, provided that, rather than, since, so that, than, that, though, until, when, whenever, where, whereas, wherever, whether, while.
Common Errors:
She'll telephone you, when she's finished. X WHEN is in the middle of the sentence
She'll telephone you when she's finished. V no comma - WHEN is in the middle of the sentence

Both Robert and Jim graduated from Cambridge University in 2002.
Don't use a comma to separate the two halves of a correlative conjunction.
Other correlative conjunctions: neither ... nor | either ... or | whether ... or | not only ... but also.
Common Errors:
We could either watch TV, or go to the cinema. X no comma!
We could either watch TV or go to the cinema. V no comma before OR

You work in an office, don't you?
A comma is used to separate a statement from a question.
Common Errors:
You are watching TV aren't you? X comma required!
You are watching TV, aren't you? V comma between statement and question

He bought a new red Mercedes.
Don't use a comma if the adjectives are not equally important or give different kinds of information.
Common Errors:
He owns several red, wool jackets. X no comma!
He owns several red wool jackets. V RED and WOOL are different kinds of information

Glen was very happy to win the competition.
Do not separate a subject from its verb.
Common Errors:
The most important aspect of the golf swing, is the grip. X Don't separate a subject from its verb
The most important aspect of the golf swing is the grip. V no comma

She complained of severe headache yet continued to work.
If the subject does not appear in front of the second verb, we do not use a comma.
Common Errors:
Steve ate breakfast and he drank coffee. X comma required!
Steve ate breakfast, and he drank coffee. V independent clause + independent clause
Steve ate breakfast and also drank coffee. V no comma - subject (HE) missing in the second part of the sentence!

Your homework should be written in ink, not pencil.
A comma is used to separate contrasting parts of a sentence.
Common Errors:
This is my MP3 player not yours. X comma required!
This is my MP3 player, not yours. V comma before NOT