Why write in third person?
1. I think the strongest reason to choose third person is if you want to get into the heads of more than one character.
2. It's easy to turn up the tension in a mystery by cutting back and forth between characters at crucial junctures, ending each chapter as a cliff hanger.
3. If the book is more about plot than it is about a character's emotional journey.
4. If you need the reader to have some distance from the character, ie, they will be going through something horrific.
5. If you want the reader to worry about whether the main character will live to the end.
6. If you have created an unusual world for the character and it would be awkward to have the narrator explain it all in first person (or to motivate that explanation).
If you only have one viewpoint character, you can decide it you want to write in first or third. So why NOT choose third?
1. If the main character has a unique world view, describing it in third person may be hard to pull off.
2. If the main character has a lot of secrets to share with the reader.
3. If you want a tight relationship with the reader and to have them identify as much as possible with the narrator.
Can you think of some more reasons to write in third?
Can you mix first and third? Sometimes. First person can be limiting, especially in a mystery or a thriller. Realistically, just how much can your main character overhear or be involved in? To get around this, James Lee Burke has his main character Dave (who narrates the story in first person) imagine things from other character's points of view. One of Robert Crais' books alternates first person (for his hero) with limited third (to show things his hero can’t know).
Here's an example of a very close third person POV from The Ruins . [Full disclosure: I HATED that book. Lots of it was well-written. I just hated the plot, the characters, the solution to the mystery, and the end. And while this is well-written, notice how much Eric hates himself. I would hope no one in real life has this kind of interior monologue.]
Eric tried to think of other words that began with mis, tried to remember what the prefix meant. He was going to be teaching English in a few weeks, and this was the sort of thing he out to now. Wrong, he guessed, or bad – something like that – but he wasn't certain. And he’d need to be certain, too, because there’d probably be students who would know, there were always two or three like that, ready to catch their teachers in an error, eager for their chance. There were books Eric had meant to read this summer, books he'd assured the head of his department he'd already read, but the summer was essentially over now, and he hadn't even glanced at them, not one.
Misstep. Misplace. Misconstrue.
That last one was a good one. Eric wished he knew more words like that, wished he could be the sort of teacher who effortlessly used them, his students straining to understand him, learning just through listening, but he knew this wasn't who he'd ever be. He'd be the boy man, the baseball coach, the one who winked and smiled at his students' pranks, a favorite among them, probably, but not really much of a teacher at all. Not someone from whom they’d ever learn anything important, that is.