Free Grammar Help — Punctuation: Commas
The use of commas is something of an art, more than a science, and sometimes they are used differently according to different styles. That's why there is often no definitive answer about whether the usage of a comma is correct in some particular instance. However, there are certain rules that everyone should follow.
Commas are short pauses in a sentence. If you read your sentences aloud to yourself you may be able to hear your comma errors better than seeing them.
To separate items in a series
Everyone knows this one, and yet so many of us get it wrong. This is because there are two different ways to do it. When we have a list, we use commas to separate items. Example: I went to the store and bought ice cream, milk, cereal, and bread. The controversy is over the last comma. It's known as the "Oxford comma," "Harvard comma," or "serial comma." British rules apparently, often avoid this comma, but it is standard usage in American English, according to the Chicago Manual of Style. On the other hand, journalists, following the AP stylebook, eschew this comma. And the APA style says it's optional unless needed for clarity. So what's a boy to do? If you are writing an essay using British English, leave it out; if you are American, leave it in. If you are a journalist, leave it out. If it's really important, check with an expert. I had a lawyer once explain to me: If Bill Gates dies and leaves $1 million to Bill, Bob, and Betty, they each get $333,333. But if he leaves it to Bill, Bob and Betty, Bill gets $500,000 and Bob and Betty split the other half mil. That's one expensive comma!
Before co-ordinating conjunctions that join independent clauses
This is a fancy pants way to say before "and" and "or." However, there is an exception that means sometimes we ignore this rule. When the two clauses are very short we can leave out the comma. Example: President Bush was elected in 2000 and he ran again successfully in 2004. But: President Bush was elected after a Supreme Court decision in 2000, and he managed a slightly larger plurality in his subsequent successful election bid in 2004.
After an introductory adverb clause or phrase
An introductory adverb phrase is a phrase that introduces a sentence, but tells us something about a verb. You might recognize it as using "before" or "after." Example: After buying the television set, Mortimer went home and set it up. Before going to the story, Jennie checked to see if she had her wallet.
To set off non-restrictive clauses and phrases
To recall, a non-restrictive clause is a clause that is not essential to the meaning of the sentence. It does not restrict the meaning. Example: George W. Bush, elected in a controversial vote, led America into an invasion of Iraq. Example: Stephen Harper, after a series of minority governments, finally got his majority in the Canadian Parliament in 2011. The non-restrictive element is just a little tidbit of extra information that the writer thought might be useful, but could be eliminated without restricting the meaning of the sentence.
OK, so there are four main rules for commas. Looks easy, yet people still make many errors, and can't agree on usage. Let's look at some of the common errors.
Common Errors with Comma Usage
Do not separate a subject from its predicate
I see this a lot in complex sentences where the writer thinks a pause is necessary to help the reader understand. It is a clear sign to the marker that you don't know your subject from your predicate. I think people confuse this with the comma needed for the introductory adverbial phrase. Wrong: Going fishing in the morning, is a good way to greet the day. This sentence could be easily confused with a similar construction using an introductory adverbial phrase: Going fishing in the morning, Bob eagerly anticipated a breakfast of fresh trout. Note that in the second example the subject is "Bob," but in the first example the subject is "Going fishing in the morning".
Do not separate a verb from its complement
This is when the writer makes the same mistake, but further along in the sentence. Wrong: Bob was fishing in the morning, for trout. Don't do this, for Pete's sake! In the example "for trout" is the object complement of the verb "fishing." The addition of an averbial phrase "in the morning" does not call for a comma.
Do not put a comma after a coordinating conjunction
Some people seem to remember that coordinating conjunctions need commas, but they can't remember where. They use them like apostrophes; they throw them in liberally and hope they land in the right place.
Wrong: George Bush attacked Iraq but, he never found his weapons of mass destruction.
Right: George Bush attacked Iraq, but he never found his weapons of mass destruction.
Do not put a comma before the first item in a series, or after the last item in a series
Wrong: I went to the store and bought, ice cream, cookies, and weapons of mass destruction, for dinner.
Right: I went to the store and bought vegetables, fruit, and roast beef for dinner.
Enjoy your dinner, use your commas safely, and please, please, don't attack another country!