Many of you here today probably are already well aware of what a Character Arc is, but for those of you that don't, aren't sure, or just think I don't know what one is; I'm going to tell you up front anyway.
At it's most basic, a Character Arc is the journey of the main character through a story and how he changes from the first page to the last. There are three main types of arcs though, which I would like to list off before delving much deeper.
First is the Change. In this arc, the main character transforms drastically over the course of the story. Luke Skywalker from the Star Wars franchise is a perfect example of this. When we first meet him, he's just a bumbling kid, thinking about tinkering with his speeder bike with his friends, working and living on a moisture farm. By the end of Episode 6 though, he's a focused, powerful, and mature Jedi Knight, ready to face not only Darth Vader, but the evil emperor as well. (This is also a good example of how a Character Arc can span multiple stories, rather than just all happening in one.)
Then there is personal growth. This means the main character changes, but not drastically. They gain experience, new skills, tools, friends, and all the exterior things, but the things that make them who they are doesn't change throughout the story. As an example, I don't think there is one better than Harry Potter from the Harry Potter series. Throughout the entire story, spanning all the books and movies, he stays true to himself, even if he does stumble a little at times. By the end of the series, he's gained a lot of knowledge and experience, but his essence remains more or less the same as the boy who learned on his 11th birthday that he was a wizard.
Lastly, we have the Fall, or the tragedy. This is the story that follows the main character in his fall from grace. They start at the top, or even somewhere in between and over the course of the story, lose everything, descending into madness, destitution, or even death. As you can imagine, this occurs in horror stories more often than others. It does pop up though. For a good example, we again turn to the Star Wars saga, specifically the rise and fall of Anakin Skywalker. (I'm only going through the prequel movies, as I know he does get redeemed at the very end, sorry if that's a spoiler to anyone.) He starts off as a young boy, full of promise and potential, and he does become a Jedi, albeit with an insufferable attitude. Then everything goes wrong, though. (POTENTIAL SPOILERS). He loses almost everything he has, his friends, his family, even his limbs, and he ends up the pawn of a dark power. And while he is manipulated, he makes the choices that brings it all about himself, which is what makes it all a true tragedy.
So there. Those are the most basic, and the most common Character Arcs you'll find in fiction. I hope I've proved that I do know of these basic storytelling premises.
But now I'm going to be somewhat controversial.
I don't believe a fully realized Character Arc is required in all stories.
Particularly if you're going for any kind of realistic characters. Face it, people get into and go through situations all the time. We may not have high adventure and things happening, but we all go through individual stories in our lives all the same. A lot of the time, people don't change or learn an earth-shattering truth; they deal with the situation as best they can and come out the other side little, if at all, changed for the experience.
In stories where it's about being in the right/wrong place at the right/wrong time, characters aren't looking to change who they are, they didn't set out on this quest to obtain something (at least at first). The story is about an event, and how characters react to it. The story isn't about growth, change, or tragedy, it's about seeing how ordinary people react to extraordinary circumstances. Change, growth, and tragedy may happen, but it's not the focus of the story.
Horror is the perfect genre for stories like that. Take Stephen King's The Shining for example. Little Danny Torrence and his mother are trapped in a horrible situation and are just trying to survive it. Few would argue The Shining is a great book, with some incredible characterizations, and you do see some tragedy with Jack's descent into madness, but that one facet isn't the sole focus of the story. It happens alongside Danny and his mother's (yes, I can't remember her name, sue me.) fight for survival against the demons that haunt the hotel and which drive his father insane. Danny and his mother don't particularly demonstrate any great change or growth, despite making it from beginning to end.
So next time you're reading, or watching a movie, if it strikes you, try to pick out the arc plotted for the main character. You may even be surprised to find there isn't one.
As always, if you disagree and want to discuss, argue, or insult me over my thoughts here, feel free to do so in the comments. :-)