One main point could be the character archetypes in detective fiction. The detective as the hero, with their own quirks and flaws. Another might be the nature of the mysteries themselves, how they are crafted to keep the reader guessing. And finally, the way detective fiction reflects the real - world social issues, even if in a somewhat veiled manner.
The main points might include the significance of clues in detective fiction. How they are planted and how the detective interprets them. Chandler may also talk about the evolution of detective fiction over time, from its early forms to more modern interpretations. Additionally, the role of the reader in detective fiction is important. The reader is often trying to solve the mystery along with the detective, and Chandler might analyze how the writer engages the reader in this process.
In Chandler's essay, he may focus on the narrative structure. Detective fiction often has a specific pattern of introducing the crime, the investigation process, and the final resolution. He could also discuss the importance of setting. A gritty urban setting, for instance, can add to the authenticity and mood of the story. Moreover, the relationship between the detective and other characters, such as the police or the victims, might be a key point.