During a visit to Thrillerfest a few years ago, I heard the same question posed to two different writers (during two different sessions). Each was asked, “How many viewpoint characters can you have?” The first author, who is successful and well-respected, answered, “Three is good. Five is the max.” When my friend Phillip Margolin received the same query, his answer was, “How many do you need?”
I’m with Phil, but I do think we need to establish some guidelines. You should have a central protagonist. Though there are exceptions to every rule, readers generally are happier when they know whose story they are following and who they are rooting for. Books with co-protagonists rarely work. So regardless of the number of viewpoints, the protagonist should have more scenes than anyone else and those should recur most frequently. I think it’s usually a bad idea to be away from the protagonist for more than a chapter.
Multiple viewpoint is more common today than it has been in previous eras. Arguably, the epistolary novel was a form of multiple viewpoint, but subsequently, single-viewpoint novels were more common. In time, though, writers realized that multiple viewpoint was a great way to drum up suspense. In mysteries and thrillers, a departure into the viewpoint of a competitor or villain allows the reader to know something the hero doesn’t–ratcheting up the tension (The Girl on the Train by Paula Hawkins). This might also give you an opportunity to make the antagonist more empathetic and less of a cardboard bad guy. In romances, multiple viewpoint–switching between hero and heroine, is more common today (A Run for Love by Callie Hutton). And you will also find it in SF/fantasy and literary fiction (The Hours by Michael Cunningham or The Help by Kathryn Stockett). Ultimately, you have to decide what is the best approach for telling your story.
I recall one of the best writers I know, David Morrill, railing against writers who introduce a viewpoint character for one chapter only (usually because the character dies at the end). For David, this is lazy writing. There’s always a better way to convey that scene than by asking the reader to become invested in a character who will never appear again. It’s not only a cheat but an unwelcome bit of misdirection. When you put your reader in a character’s viewpoint, you suggest that this character is important. They will not be pleased to learn the character is simply a victim. And it’s always a bad idea to introduce a new viewpoint just to drag in some exposition or infodump.
And now, having established the rules, let me explain how and when I broke them. When I wrote the last Ben Kincaid courtroom drama, Capitol Offense, one of the topics I wanted to address was the common law enforcement policy of not pursuing lost-person reports from a spouse until someone has been gone a long time, often as long as a week. Their excuse is that, in most cases, there’s been a squabble and the spouse has simply run off. But this policy has led to many tragic results. In my novel, Ben’s client was devastated by the loss of his wife–because the police waited too long to look for her. I wanted the reader to feel his pain, and to me, that meant they needed to know his wife personally. So I introduced the wife in the first scene, her work as an oncologist for children, her sense of humor, her great love for her husband. Obviously, she did not survive far into the story. But I still felt the excursion into her viewpoint was justified.