Monthly Obscure Trope Series — Cast Calculus

So, how does a writer figure out what characters they should put in a story? We’re not talking powers necessarily here—we’re talking about personalities.  

The answer depends on how many main characters there are in a story. 

Don’t worry about villains or side characters. Just main characters—just the ones that are central protagonists. 

And don’t worry if you weren’t any good at math in school, because Cast Calculus doesn’t involve any actual math. Not really. 

I’m going to teach you the easy way to do Cast Calculus, but if you find yourself wanting more information, definitely check out the link to TV Tropes. 

Let’s get started.

When we talk about casting characters for a story, there’s one rule to, well, rule them all: Each Main Character must be different. Each MC must stand apart from the others in some way. Sometimes this is powerset, skills, moves, etc, but the better way to do it is with personality. 

Second, remember that personality traits are finite—there’s only so many different ways to describe a character. 

Third, the more MC’s you have, the more overlap there will be in personality traits. You might have two plucky comic reliefs or two stoic mentors or two badass fighters. 

Let’s start with Two MC’s to illustrate this point, and let’s use the quintessential example of Sherlock Holmes and Dr. Watson. When we’re dealing with just two MC’s, there’s a lot of personality to divide up, and so Holmes and Watson feel like very different characters. Holmes is analytical, rash, and callous. Watson is very much the opposite in all three aspects. Sometimes it seems like the only things they have in common is that they both solve crime and they’re both experts in their field. Try to think of any other personality aspect and I wager that the two characters are polar opposites. 

And for a contrast, let’s look at Firefly, a space western TV show (short-lived but awesome), and one with a large ensemble cast. There are nine MC’s. As you can imagine, there’s quite a bit of overlap in some of them. Just looking at the personality traits we looked at in the previous example: Jayne, Simon and Summer are rash. Mal and Jayne are callous. Simon and Zoe are analytical. Wash handles quite a bit of comic relief, but the jokes are pretty evenly spaced between characters. I’m painting with broad strokes here, but you get the picture. The more MC’s you have in a story, the harder it is to differentiate them because there are only so many personality traits to go around. Lean too heavily into this and you risk your MC’s becoming one-dimensional caricatures. 

Three and four Main Characters tend to be sweet spots for stories. Part of the reason Kirk, Spock, and McCoy mesh so well together is because of the division of personality between them. Same goes for the Teenage Mutant Ninja Turtles with Leonardo, Michelangelo, Donetello, and Rafael. 

Try thinking of some of your favorite books, movies, and media… How many Main Characters are there? How are personality traits divided amongst them?

But what about if you only have only one Main Character? What if you’re working with a character like Conan the Barbarian, a wandering samurai, or a lone gunslinger? 

There’s a reason why a lot of stories have multiple Main Characters—character relationships add depth to a story. So, how do you make up for this kind of depth if you only have one Main Character?

Well, it’s tricky. There’s a reason why a lot of single MC stories tended to be lone warriors wandering through the world. Each story was them wandering into a new town and meeting new characters. Sometimes these side characters became borderline MC’s for that single story. The town and the inhabitants were as much Main Characters as the hero is. 

What about you, what’s your ideal number of Main Characters? Post your thoughts below.

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