In psychological testing, internal consistency refers to how well items on a particular test measure the same construct. In principle, items that purport to measure the same construct should strongly correlate to each other. We can make use of a similar idea when writing fiction.
A story is made up of multiple components, and it has internal consistency when all of these components operate and abide by the rules and logic that govern the world the story is set in. In other words, internal consistency in a story refers to how closely the components of a story adhere to the rules and logic set out by the story itself.
But why does the internal consistency of a story matter?
Let us begin by considering a fantasy story in which the characters possess magical powers. Magic, almost by definition, allows people to do things that would otherwise be impossible (e.g., create and control fire). But magic is not random – it cannot be if the story is to make any sense.
Try to imagine what a fight between two characters with magical powers would be like if there are no rules about how magic works and what it can do. It would be utterly ridiculous. So much of the tension in a fight scene derives from the combatants pitting their strengths and weaknesses against each other. But without rules or logic, there are no strengths or weaknesses. Characters could simply do whatever they please without any limitations whatsoever.
If there are no rules, could characters even run out of magic? No. Being able to run out of magic is one of the most common rules in fantasy fiction. Would there be different types of magic? No. It would be impossible to distinguish between different types of magic without rules or some kind of logical classification system. Could characters simply alter reality on a titanic scale and simply will themselves to victory? Quite possibly. Rules and logic are what set the limits on what magic can achieve. Without them, there is no reason to limit what characters with magic can do (which would make for a thoroughly boring story and fight scene).
Internal consistency is also vital because it allows the readers to engage with the story. Readers typically enjoy thinking about the characters, plot, settings, and ideas of a story. But thinking about these things in a meaningful manner involves trying to understand and even predict them, and understanding and prediction are impossible without rules and logic.
Think about the plots for all of the stories that you’ve read. How many of them involved twists and surprises? At least a few of them probably did. What made those twists and surprises good? It wasn’t just that they caught you off guard. It was almost certainly because those plot twists and surprises made sense in retrospect.
Consider the film The Sixth Sense. What made the twist at the end so enjoyable was the fact that all the evidence was there – everything that the viewer needed to reach the correct conclusion was given to them before the twist was revealed. As a result, the viewer did not feel cheated by the twist. On the contrary, there was a sort of “eureka!” moment when everything made sense. That feeling would have been impossible if the movie had not explained the rules and logic related to the child’s power.
We can also see the importance of internal consistency in science fiction.
It is not unusual for science fiction to be set hundreds, even thousands, of years into the future. As a result, highly advanced technology (e.g., faster-than-light travel) is quite common in science fiction. One of the keys to making science fiction enjoyable is to provide firm rules and sound logic about how all of the advanced science works.
Think about the classics of science fiction (e.g., the work of Arthur C. Clarke and Isaac Asmiov). The wonders they describe are not simply thrown out into the open for the reader’s consumption. Instead, they are contextualised. For example, Asmiov’s robots and psychohistory all obey clearly defined rules and logic, which makes understanding and enjoying his stories much easier.
The importance of internal consistency can also be applied in a less genre-specific sense.
How characters behave is another area in which internal consistency is important. In general, human behaviour is not random. People behave the way they do for a reason. Readers can become disenchanted with a story when the characters begin to behave in ways that do not make sense. For example, if a character has behaved rashly for 99% of a story, it would be very odd if they suddenly became thoughtful and considerate without a good reason. How a character behaves throughout a story establishes the rules and logic that govern their future behaviour. This isn’t to say that a character must always act the same. Instead, it means that large variations in behaviour need an explanation. Otherwise, readers can be left feeling puzzled and confused.
The plot likewise needs to operate according to sound rules and logic. One of the reasons that all of the plotting and scheming in A Song of Ice and Fire is so entertaining is because it makes sense. The readers may not always agree with the direction the plot takes or even like the direction the plot takes, but they can agree that it is believable. And why is it believable? It is believable because the plot operates according to rules and logic that have been set out earlier and which take into account the characters, the culture, and the themes of the story.
Even the setting of a story needs to have internal consistency. Consider a story set in a world that has adopted a completely authoritarian style of government. That alone provides a set of rules that define the limits of what characters can and cannot do without attracting attention. Likewise, if a political thriller is set in the present day Middle East, then the setting itself needs to be commensurate with what we know about the Middle East, with that knowledge also having implications for the plot and characters.
Internal consistency is about ensuring that a story makes sense. When a story makes sense, it is far more likely to engage and entertain the reader. This is particularly important in fantasy and science fiction, which already require suspension of disbelief. Asking readers to suspend their reasoning and logic is a recipe for disaster.
If you want to read more about my thoughts on writing, you can find those here.
I also write original fiction, which you can find here.