Comma Rules· Use a comma before a coordinating conjunction (and, or, but, nor, yet, for, so) separating independent clauses, statements that can stand alone.
The envelope was made of yellowish parchment, and the address was written in emerald-green ink.
Harry knew he ought to feel sorry that Mrs. Figg had broken her leg, but it wasn?t easy when he reminded himself that it would be a whole year before he had to look at the cats again.
· Use a comma after an introductory word, phrase, or clause that comes before a main clause.
Strangely, the snake winked.
Once, Aunt Petunia had cut his hair so short he was almost bald except for his bangs.
About once a week, Uncle Vernon looked over the top of his newspaper and shouted that Harry needed a haircut.
For a split second, he thought he was going to fall.
Not wanting to miss anything, he got some of everything.
According to the large clock over the arrivals board, he had ten minutes left to get on the train.
· Use commas before and after a quotation within a sentence.
He managed to say, "Go, cupboard, stay, no meals," before he collapsed into a chair.
"Oh, we're not working," Harry told him brightly.
· Use commas around words, phrases, and clauses in the middle of a sentence when they aren?t essential to the meaning of the sentence.
Next morning, however, he had gotten up to find his hair exactly as it had been before.
The Dursleys knew that the Potters had a small son, too, but they had never even seen him.
If anyone looked out of their window now, even beady-eyed Mrs. Dursley, they wouldn?t be able to see anything that was happening down on the pavement.
There, reflected behind him, were at least ten others.
They were carried along a dark tunnel, which seemed to be taking them right underneath the castle, until they reached a kind of underground harbor.
There was a large birdcage, which had once held a parrot that Dudley had swapped at school for a real air rifle, lying in the corner.
· Use commas to set off geographical names, items in dates, and professional titles.
Can we see all this in London, England?
Items in dates or addresses
It said 'Mr. H. Potter, The Smallest Bedroom, 4 Privet Drive, Little Whinging, Surrey and was addressed July 31, 1997.
Minerva McGonagall, Deputy Headmistress, was in charge.
· Use commas between items in a series.
Harry tried to remember, left, right, right, left, middle fork, right, left, but it was impossible.
Smeltings boys wore maroon tailcoats, orange knickerbockers, and flat straw hats called boaters.
They always complained about the school's brooms: some of them started to vibrate if you flew too high, some always flew to the left, some just didn?t fly.
I've heard he's sort of a savage, lives in a house on the school grounds, gets drunk, and ends up setting fire to his bed.
It didn?t so much as quiver when a car door slammed on the next street, nor when two owls swooped overhead, nor when a mouse ran over its tail.
He couldn?t direct it at all; it was zigzagging through the air, and every now and then making violent swishing movements that almost unseated him.
· Use a comma before an afterthought or contrasting element.
For Harry, the chance to be at school was vitally important, far more important than it was for the others.
In the weeks that followed he did seem to be getting paler and thinner, not more robust.
Examples taken from Harry Potter and the Sorcerer?s Stone by J.K. Rowling.