I have recently read several inexperienced writers discussing the themes of their works. One suggested their themes always put their characters into a wood or forest. Another that the characters turned out to be related. These and other mentions of themes made it clear that what the theme of a novel or a short story is, may often be misunderstood.
In contemporary literary studies, a theme is a central topic, subject, or message within a narrative. Themes can be divided into two categories: a work's thematic concept is what readers "think the work is about" and its thematic statement being "what the work says about the subject". Themes are the broad background of the story. Some common themes in literature are "love," "war," "revenge," "betrayal," "patriotism," "grace," "isolation," "motherhood," "forgiveness," "wartime loss," "treachery," "rich versus poor," "appearance versus reality," and "help from other-worldly powers." In other words, the themes are the lesson, moral, or the message of the story.
To identify the theme, be sure that you've first identified the story's plot, the way the story uses characterization, and the primary conflict in the story. It is the idea the writer wishes to convey about the subject—the writer's view of the world or a revelation about human nature.
The Edinburgh Crime Mysteries are police procedural thrillers. Whatever the plot style, the defining element of a police procedural is the attempt to accurately depict the profession of law enforcement, including such police-related topics as forensic science, autopsies, gathering evidence, search warrants, interrogation and adherence to legal restrictions and procedure.
The recurring themes of my novels include the general idea or theory, such as ‘all people are inherently selfish’ (although a pessimistic one). Or I may tackle themes in even broader terms. A reviewer might say I examines themes of ‘crime and punishment’. The events of the stories might make the reader ask, ‘Why do criminals break the law?’ or ‘What is the real purpose of punishing a crime?’
I also explore the more detailed themes of love, loyalty and teamwork. It doesn’t matter whether the characters are in a wood or whether they are related, the themes draw the bigger pictures of the stories and their underlying meanings.