CoherenceCoherence is a term that I use to assess a character. A good character has a high level of coherence. Coherence requires that a character be predictable, understandable, and reasonable. Incoherence is when a character acts is not predictable, understandable, or reasonable within our understanding of the character.
A cashier who rings up Joe’s groceries and the waitress who delivers Joe’s milk are coherent characters. They act according to their jobs. As a reader, you know what a waitress and a cashier do. You predict their behavior. You can even predict their motivations and what would distress them, such as demanding customers or the need to buy baby a new pair of shoes.
Your primary characters should be reasonably predictable, understandable, and reasonable. Your overly-excitable character should get overly-excited at times, the dry witted should have dry banter, and the street smart cop should show his street smarts. The limit here is that your lead characters should be finitely predictable, understandable, and reasonable. Sometimes he is going to order a different drink, react in a different way, or choose a different option because of where he or she is in the story.
Strive for coherence. This quality greatly aids the illusion of character depth. Once these known traits exist, your audience will fill in the rest of the details from their own imagination. You can even leave these traits out and the reader will fill them in.
Most importantly, a coherent character is a re-creatable character. As you write your character, that character will be involved in scene after scene, and you need to be able to capture their personality every time. The person recreating the character is you every time that you write.
An incoherent character gets torn apart by your readers. Their inherent instability and unpredictability pushes the reader away from the story. They can’t get to know and like someone who acts in a way that makes no apparent sense from scene to scene. An incoherent character provides no engagement for the reader. Every surprise is a surprise in the most literal sense as the writer picks reactions for the character that make no sense to the reader.
In the end, coherence is just an illusion. There is no real person, after all. In its simplicity, coherence is how well you maintain that illusion.