[Update: due to some well-reasoned commentary on this article, I’ve changed the title from its original to what you see now, and have adjusted other text in this article to match. If you care what that means, you can read all about it in the comments.]

Recently I wrote that writers need to develop a kind of multiple personality syndrome. I won’t say “disorder” because as it applies to writers, it’s actually a good thing. Then last week someone made a comment on my article about boring characters which touched on the notion that boring characters don’t have a well-developed sense of theory of mind.

That got me thinking. Dangerous, I know, because realizing how these two things are related leads to heresies like this one: You know that old rule about how you can break any of the rules of writing, as long as it works? Here’s one you can’t break. Here’s a new rule that, I claim, is not a rule but instead a fundamental law of fiction.

Writers must have a strongly developed theory of mind.

That is to say, your books are doomed to suck until you really understand theory of mind. This, although I didn’t quite realize it when I wrote it, is what I meant in that earlier article when I was talking about multiple personalities.

What is “theory of mind?”

Click the above link and Wikipedia will tell you it is “the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires and intentions that are different from one’s own.” That’s actually a pretty good definition, and I’m not going to mess with it.

Why you must understand it

Theory of mind has everything to do with writing, because it has everything to do with creating believable characters. Unless you’re writing an autobiography (in which case, you’re not writing fiction and you’re reading the wrong blog right now), you can’t create even one believable character without being able to model the mind of someone other than yourself.

You create a believable character by imagining a set of beliefs, desires, knowledge, and so forth that are different from your own. This is a model from which you can then determine how a character will act, react, and speak in a given situation. Using your model—your theory of the character’s mind—is how you keep your writing true to how the character would really be.

Now do this for every character in your book, and develop the ability to keep all of these different theories of mind straight within your own head while you write your scenes. This is nothing if not controlled multiple personality syndrome.

Understanding the theory of mind on this level is necessary to create believable characters. I would argue that most successful writers do this in “gut feel” terms, rather than in analytic terms. But however you get there, you simply must have a strong sense for how the minds of other people work if you are to write believable characters.

That’s table-stakes, the minimum requirement for creating believable characters. But what happens when you understand theory of mind on a deeper level? What happens when you realize that part of your theory of mind about any of your individual characters should include that character’s own sense of theory of mind about others.

This can get confusing pretty quickly, so re-read that a couple of times if you have to.

What can you do with theory of mind

When your theory of mind about a character is rich enough to include whether the character’s theory of mind is poorly or strongly developed, then you can start to play with it to achieve some specific effects:

• Boring people. As I talked about in my last article, boring people don’t have strong insights into other people’s minds. Boring people are deficient in the ability to infer what other people think about them. Boring people, as it were, have a weakly developed sense of theory of mind which makes them blind to how others perceive them.

• Children. Small children of age 4 or thereabouts, give it take a year or so, haven’t yet figured out theory of mind. A kid may be plenty smart, possessed of sharp mental faculties, they just haven’t yet determined that other people have minds different than their own. Determining when and how theory of mind develops as children mature has been the subject of countless research studies, but for you the writer, you can use theory of mind to help portray young children. It shows up most readily in modeling other people’s factual knowledge about the world. Young children tend to believe that everyone knows the same set of facts that they do. So, for example, to a young child the game of hide-and-seek is entirely pointless: they can hide anywhere they want, but as far as they’re concerned, the seeker will automatically know where they have hidden, because they themselves know where they are.

• Deception. Speaking of hide-and-seek, theory of mind lies at the root of all deception. You cannot intentionally deceive someone else without having a good theory of the other person’s mind. Deception is all about manipulating the other person’s beliefs, usually as a means to affect the other person’s actions. But, you cannot do that without first having a good sense for the other person’s beliefs, knowledge, and goals. If you understand the other person on that level, you can predict how they will behave, and thus, you can figure out how to manipulate their beliefs in order to induce them to act how you want. Or, as Friends so aptly put it, they don’t know that we know they know. Note: if your theory of mind about the other person happens to be wrong in some key aspect, the person’s reactions to your manipulations might really surprise you, which is itself a great strategy for novelists to employ.

Walking in many people’s shoes

Don’t resort to taking meds or anything, but strive for this controlled multiple personality syndrome. Like any skill, you have to work on it. It’s not just a good idea, it’s the law. “Black’s Law,” if I may be so cheeky as to label it: Writers must have a strongly developed theory of mind.

If anything, your proficiency with theory of mind must be stronger than normal because it’s not enough to simply understand theory of mind. You also have to know what to do with it.