When I speak of "rules", I speak of the conditions that define and limit fantastic subjects, such as monsters, super heroes, and magic. The basic "natural" laws that allow what would be impossible in the real world. What the supernatural and preternatural can and can not do.
Read enough Fantasy and Horror and you'll see them crop up with great regularity. Same holds true for Science Fiction, of course, but let's put that portion of the talk off for another day.
An excellent example of rules in the Fantastic Genre would be Gremlins, specifically for the Mogwai. They are:
The first rule sets a limitation, the last two are powers the creature has. How the Mogwai and the Gremlins behave during the movie is defined by their rules. Each one has consequences when broken and the consequences are fully explore.
Without rules, you have characters and creatures who can do anything. The most common example for this is Superman. Back in the day, he had super-this and super-that. If he didn't have a power to match the situation, you could bet he'd whip something up that would work. On all of this he tended to be a step or two ahead of everyone else he dealt with.
This isn't, of course, to say Superman had no rules. Green Kryptonite kills him, he's weak against magic, and so on. However, all of this was put into play after the fact. When the Last Son of Krypton could do anything that needed done, it became a bit difficult to write for him. Thus these weaknesses (rules) were given to him.
Another excellent example is Bugs Bunny. That Wascally Wabbit can do whatever the script requires of him. Seldom, if ever, are we concerned about his well being. We laugh at his antics, we enjoy his triumphs, but how involved are we in his life? Especially when we know the next time we see him, he'll be in a whole new situation.
The rules of anything, be it monster or magic spell, super hero or super villain, should be expressed, if not early in the proceedings, then well before the tale is coming to a conclusion. Doing otherwise runs the risk of giving the story the meddling of a Deus ex Machina. Which, as we all know, is a Bad Thing.
You also run the risk of alienating the readers if the rules you're playing with aren't the same as the ones they are expecting.
As a for instance, what are the rules for classic werewolves?
Depends, of course, on what you consider "classic", doesn't it?
That in mind, I would say that the rules most people would recite would be are as follow:
A person becomes a werewolf due to being bitten by a werewolf.
They change into werewolves on the rise of the full moon.
Silver bullets (or silver in general) kills them.
Pretty standard, right?
Except when I think "classic", I don't think of those rules. They're "Hollywood Classic", stemming from Curt Siodmak's work in The Wolf Man. They work, but, for me, the old ways are best. A wizard wearing wolf skin, using his arts to disguise himself as an animal. A baby born on Christmas Day becomes a werewolf in his manhood. Regular weapons work just as well as silver. Stuff like that.
If I was to use one of these types of classic werewolves, it would behoove me to mention it. That way, when the main character doesn't wolf out over being bitten or my werewolf dies in a hail of real bullets, the readers are neither surprised nor disappointed.
(Unless, of course, they prefer reading about "Hollywood Classic". But that's another ball of wax.)
One further thing about rules. Sometimes their very existence leads to story ideas.
Let's look back at The Wolf Man and his rules. In addition to the three I mentioned, his victims are marked with a pentagram. This suggests a mystical connection to the curse. Coupled with how the curse spreads, this leads to several questions:
Who was the first Werewolf?
Why was he (or she) cursed?
Who cursed them?
Why is the curse spread at all?
How are the victims chosen? What if one escapes? is another one chosen the next night? Or does the werewolf keep trying until he (or she) gets it right?
Why, exactly, does silver kill werewolves? (Iron, traditionally, was a bane to magical creatures. Why not iron instead of silver? Or as well as silver?)
Why limit the transformation to the full moon? Is it tied to "the crazies come out for the full moon" myth?
As I recall it, none of these points are addressed in the movie. None of them really needed to be, either, any more than the restrictions placed on the Mogwai needed to be dwelt upon. However, by having an answer, even if you never reveal it outright, you can in theory enrich what your writing.
Or, at least, that's what I keep telling myself as I work on my endless notes.
