“What is your story theme? What is your story really about?” I ask.
“It’s about a boy who embarks on a journey to find his long-lost sister—,” you answer.

“That’s not what I mean,” I say, interrupting you. “By theme I mean the essence of your story, distilled into a single sentence.”

Without it the tale is rendered rudderless. 

In his book, The Moral Premise, Stanley D Williams explains that the moral premise (substitute the word theme here) is the force that determines the flow and direction of events in a story. He asserts that stories with a strong moral premise do well at the box office. He sites films such as Star Wars and Braveheart as examples. Here, the claim is that understanding the moral premise guides the writer to craft a story that stays on track.

So, what form does the theme take? Williams says it isn’t enough just to state the one side of it.

“The story theme is the compass that allows the writer to navigate through a myriad of narrative outcomes.”

In the novella, Before the Light, for example, one part of the theme might be: Too much knowledge heaped upon an unprepared humanity leads to destruction (followed by the second part), but a well-kept secret leads to survival.

This creates an appropriate springboard for character action, for the story to explore the possible consequences of each possible outcome. The sentient quantum computer, Icarus, for example, has to choose between fulfilling the duty entrusted to it by its human creators, and risk dragging the entire world into a war, or betray the very purpose of its creation.

The story traces the tension between those two irreconcilable outcomes, right up to the moment in the climax when a decision is made—with all its concomitant consequences.

The complete moral premise, or theme, therefore, represents the genetic code for a story and takes the simple form: If X leads to a bad outcome, then MINUS X leads to a good outcome. A fully articulated theme allows us to navigate the terrain between those outcomes using this structure.

Summary

The theme or moral premise, comprises of two parts and can be thought of as the organising force of any story: One part identifies the virtue which leads to victory, while the other identifies its opposite, which leads to defeat. Keeping the theme in mind allows you to craft a story that stays on track.