SO, punctuation marks: the footsoldiers of communication. I've called them pixies because they are a tricksy little bunch. They look all friendly and sweet, but if not treated with respect, they can reveal their gnashy little teeth and go you.
That said, the rules of punctuation are not difficult. There is some room for flexibility and personal style, and some degree of interpretation on the basis of nationality and formality of communication. I'm going to give a basic introduction and rule set below, but with a slant towards fiction. And while 20 years ago I would have given a long description of the differences between English and American standards, the internet has seen those differences start to crumble. In addition, some styles that are rigidly adhered to in books are not used at all in newspapers or magazines. I'll mention a few, but for the most part I am using the styles most commonly used in publishing.
There are two levels of 'rules' for punctuation. The first level consists of actual rules, the second level is a matter of style. While most of the below are rules that should be followed, I have mentioned some style points beyond just the national styles, each is marked as such.
Learn the rules and use punctuation clearly and your beta will be happier, your writing smoother, and the mods at certain archives will have nothing to whine about.
Now I am writing from my position as a professional writer and editor of over 20 years' experience, but the one thing that experience has taught me as a certainty is that whenever one makes declarations on this topic, there will be others who disagree passionately. If you have a serious disagreement with any of the following that you would like to discuss at more length that the comments allow, feel free to get in touch via blamebrampton at gmail dot com and yes, there are almost certainly typos in this entry, my typing is rubbish. Feel free to mention them and I'll edit.
The full stop/ the period/ the end stop
This is the building block of the sentence. A sweet, easy punctuation symbol, it finishes off most sentences and can also be used to show a contraction and an abbreviation.
This second usage is mostly falling out of use. Where it was once appropriate to write Mr. D. Malfoy, Esq., one would now write Mr D. Malfoy in the same circumstance [although as esmestrella kindly reminds me, Americans would clutch those periods to their gentle bosoms]. Indicating an initial is the major remaining use of the period other than ending a sentence.
The most popular punctuation symbol, this is another one that is hard to get wrong. It's used inside a sentence, to indicate a pause, usually between clauses. The rule of thumb that I was always taught as a child is that a comma should be used wherever you pause in a sentence.
Now there are sometimes better options than the comma. The colon, semicolon and dash entries below will cover off these options. In general, a comma works where you are still talking about the same main idea, but need to break up the sentence.
* You might need to break it to indicate that another piece of evidence is being added to the idea of your sentence:
Harry looked at Draco and tried to find any sign that he was lying, but his eyes were clear, his gaze earnest, and his brow frowning with his desperation to convey this truth.
* You should use commas to break up simple lists, which are all elements of the one idea:
Harry, Hermione, Ron, Ginny and Neville were all seated at the dinner table when Seamus walked in.
For really short lists, you sometimes don't need a comma. So while the classic it was a dark, stormy night should take a comma, the bad-tempered blond wizard does not require one, as the terms in that list are acting together, rather than strictly as a list.
In most cases there is no need for a comma before the final 'and' in a list separated by commas, but sometimes the sentence works better if you add one, such as:
We had dinner with Harry and Draco, Ron and Hermione, and Neville and Hannah.
I know that Americans love the Oxford comma, which is what the comma before an 'and' (such as the one above) is called, my theory is that it generally does no harm.
* You should also use commas to set off some words from the rest of the sentence:
Hermione had had enough of Ron and Harry, and Draco, too.
However, if you steal a Gringotts dragon, you must expect heavy penalties for future early withdrawals.
Goddamit, you have got to be joking.
* You should use a comma in most cases before or after direct speech:
Draco said, "I cannot possibly be seen in public with your hair."
"I cannot possibly be seen in public with your ego," Harry replied.
* You should use commas in pairs to break out weak interruptions to a sentence.
Grimmauld Place, which was the most miserable house Draco had ever set foot in, had the virtue of being well-protected by wards.
And use single commas to break off these sorts of interruptions to a sentence when they occur at the beginning or the end:
Though it was the most miserable house Draco had set foot in, Grimmauld place had the virtue of being well protected.
* You can also use a comma to show that two or more ideas are all part of the one idea or experience:
Draco was trying to stay alive, Narcissa was lying for Harry, Lucius was simply trying to protect his family.
though often a semi-colon is useful for this sort of sentence when the clauses/ideas are longer or less closely related.
* Finally, there are some 'rules' to the comma that are actually bollocks. The three that are trotted out the most are that you should never use a comma before an 'and', and that you always need a comma before 'but' and before 'which'.
Commas before 'and' are actually fine, both when used in a complicated list as above, and if they are functioning as any other comma would function. Just like that one there.
While a comma before a but is often a fine and worthy thing, it can also be unnecessary in short sentences where the meaning is clear:
He was tall but not gangly.
Sometimes the comma helps in short sentences like this, it's a matter of rhythm:
She was short, but did not look it.
As to which, the rule is that you need a comma before a which every time that it is being used in a nonrestrictive clause. This is a clause (a part of a sentence) that adds information that is not essential, like this one:
The tenth anniversary, which Harry was avoiding, was the best-attended ceremony yet.
For restrictive clauses, ones that add meaning that is essential to the sentence, you don't need a comma. These are all cases where the which could be replaced by that. Such as:
It was the emotion which was furthest from Harry's mind at this time.
So if which could be replaced by that, no comma. If it needs to be which, you need the comma.
ETA The ever-courteous catsintheattic asked for more clarification on this point. Here is some. The that/which thing is all about the information. If it is essential to the sentence, then it's best to use that, though you can use which, and either way you don't need a comma. So you don't need commas in sentences like:
The shirt that Harry was wearing was tattered and torn.
The diary which Harry was carrying belonged to Tom Riddle.
In the second case, the which could (and probably should) be replaced with a that. Journalists use which all the time because they think it makes them sound important.
But you do need commas in these:
The diary, which Ginny had previously thrown down the loo, belonged to Tom Riddle.
Harry was wearing his enormous shirt, which had been handed down by Dudley on the basis that it was 'crap'.
In each of these cases the additional information is not essential to the sentence, and the which could not be replaced with a that.
Not a part of the digestive system (BOOM BOOM!), this is a more significant internal pause than the comma, and used in very particular ways. Most often, it is used to introduce a specification. So:
Draco Malfoy had one simple imperative: survive.
Harry had rescued many people in his life: Draco Malfoy was just another person.
In all of these cases, the second part of the sentence follows on directly from the first
You can also use a colon when you reverse a specification and the rest of the sentence.
Survival: that was the only thing that was essential to Draco now.
Colons are also used to introduce lists:
There were many options now: become an Auror, study advanced DADA, convince Draco to live in the study as his sex slave … Harry was finding it hard to decide.
Colons are also used at the beginning of lists of examples:
Colons can also introduce quotations:
As Harry Potter was fond of saying: "He may be an ex-Death Eater, but he's a very tasty ex-Death Eater."
From the abuse it often suffers, you might think this is the tricksiest punctuation mark of them all, but it is in fact relatively simple to use. The semicolon is used to separate independent clauses within a sentence. So:
Harry was jubilant; Draco despondent.
The death of Voldemort marked the end of Draco's planned life; from hereon in he was free and unfettered, able to choose for himself.
Note that these two clauses could be shifted around to function as separate sentences, but by putting them together, more meaning is generated through their proximity. And usually there is a better rhythm to the prose than you would manage by spelling out the ideas in separate sentences, too.
Semicolons can also be used within complicated lists that contain internal commas. Like this:
"Right," said Ron. "This is how everyone met: Hermione and I were best friends at school who fell in love while hunting Death Eaters; Hannah and Neville were shy, retiring types who bonded over a shared love of heroic stances and absinthe; and Harry and Draco were lifelong enemies, though we always had our suspicions, who were thrown together in unlikely situations where shagging was the only narratively satisfying outcome. So how did you meet your wife?"
The exclamation mark/point
In newspapers and mags these are often called screamers or slammers (or indeed a dog's cock, I am told, in less genteel circles). They are considered something to be removed wherever possible, and I have to say that this is not a prejudice without reason. They are usually a sign of bad writing and stop you looking for more imaginative ways to convey apprehension in particular, compare:
"But there are Death Eaters everywhere! It's not safe!"
"So we walk into the Ministry and walk out again, and no one will notice a thing. Sure. That sounds like a brilliant plan. Let's rob Gringotts while we're at it."
Harry listened carefully to the plan. Hermione was right, there was no choice but to go into the Ministry. He hoped he didn't look as ill as he felt.
That said, they have their purposes.
Molly snatched her hand back, and Arthur bustled past her to throw a hessian sack over the gnome.
"Sorry, love, that one's been frothing at the mouth all day and Ron thinks it has rabies."
"Ron!" Hermione squeaked. "Other people can see where your hands are!"
Interjections are a special case and can often be followed by an exclamation mark without any problems. So, Bah! Gah! Argh! and Yay! are all perfectly fine and can be used freely so long as you do not go completely bananas with them.
The question mark
This one is pretty obvious. If it's a question, it's best to conclude it with a question mark. While the English question mark lacks the subtlety of the Spanish, it is a very helpful little mark. On the whole, it is used at the end of any sentence that you would say out loud in an interrogative fashion.
"Are you wearing that?" "Do you think he has a Dark Mark?" "Were the Death Eaters wholly committed to Voldemort, or did they begin as a movement more concerned with traditional Wizarding values?"
You can also use a question mark within a sentence to show that a part of that sentence is a question.
Narcissa and Lucius Malfoy took three years to return to their post-war position in society – and did it feel the same to them? who can say? – but were never again as prominent in Ministry politics after the War.
Some questions don't need a question mark.
Harry wondered if he would ever know an easy night's sleep, but supposed it would be a question better answered once Voldemort had been dealt with.
"He wants to know if you took the mark, Draco. Keep your sleeves down."
This is the name for those three dots that you use to indicate something trailling off or missing. They look like this: … and note that there are three dots, not four, not five, three. On a Mac, this symbol is option + ; which may well be control + ; on a PC, this exercise is left to reader. azurelunatic reminds me in comments that much of the world lives in an html age:
will do the trick there.
Ellipses are fun when used with restraint. They stand in place of words or letters that have been omitted and there are slightly different rules for how they are used depending on whether they stand for words or symbols. When words are omitted (including when shortening a quotation) or a sentence trails off, there are spaces before and after the ellipsis. When letters are omitted from a word, there are no spaces, unless the missing letters are at the end of a word in which case no spaces before, but a space afterwards, unless it's at the end of a piece of speech, when the quotation marks will be hard up against the ellipsis (i.e. no space).
I know that you Americans love to butt all of your ellipses up, eschewing spaces, but this fails to preserve a useful distinction in the usage. And it looks ugly, too.
Oxford insist you should add a full stop after an ellipsis at the end of a sentence. But this is madness and a rule that is fast falling out of use in English publishing. Outside of OUP, I am hard-pressed to think of anywhere that still firmly believes in this style.
I realise that this is all sounding a bit complicated, so just follow these examples.
1. Trailling off. "I don't know why I'm following him, he's just …" Draco shrugged, there was no way to explain it.
2. Words missing. "This is the BBC World Service. Tonight in … earthquake has shaken … many feared dead … our man on the scene …" George fiddled with the radio, but there was no improving the reception.
3. Letters missing. "Harry, have you seen my hairbr… Oh you must be joking."
OR "You f…cked up, maggot-breathed c…ck!" Charlie censored himself.
OR "I'm falling asleep, talk more tomor…"
Part B will be written shortly (er, probably) and will look at the apostrophe, the quotation mark, the dash, the hyphen, the parenthesis, the square bracket and anything else that I can remember I've forgotten between now and then.