A few observations about noir fiction tropes after spending too long rereading the wrong people's books:
Dashiell Hammett was a Pinkerton detective before he became a writer. You can feel it in every sentence he wrote. His prose doesn't describe what characters think or feel. It describes what they do with their hands, where their eyes go, how long they pause before answering. The behavioral surface is the whole story. What's underneath stays underneath, and the reader has to fill it in.
The difference between hardboiled and noir is simple and it matters more than most craft books acknowledge. In a hardboiled story the detective gets beat up but survives. He walks away bruised and wiser. In noir the protagonist doesn't make it out. Hardboiled is about endurance. Noir is about inevitability.
S.A. Cosby proved that noir doesn't need cities. Blacktop Wasteland is set in rural Virginia, and the desperation runs hotter there than in any rain-slicked alley in Los Angeles. When your character can't afford to fix his transmission and a crime job pays what six months of honest work won't, the geography becomes irrelevant. The economics are the setting.
Short sentences are noir's native rhythm. The paragraph breathes in clipped bursts. When a noir sentence runs long, it's usually because the character's composure is unraveling and the syntax is starting to unravel with it.
Hammett once said, "I stopped writing because I was repeating myself. It is the beginning of the end when you discover you have style." I think about that constantly. The implication is that style is a form of calcification, that once you can hear yourself you've stopped listening to the story. Most writers spend their careers trying to find a voice. Hammett quit the moment he found his.
The femme fatale is the most misunderstood trope in noir. Brigid O'Shaughnessy in The Maltese Falcon isn't dangerous because she's seductive. She's dangerous because she's smarter than everyone in the room and uses their assumptions about her as cover. The trope works when the woman's intelligence is the threat.
Noir is the most honest genre in fiction because it starts where other genres pretend you'll never end up. The system is broken. The institutions are corrupt. The people in charge are worse than the people they're chasing. Every other genre lets you believe, at least for a while, that the structure holds. Noir opens with the structure already collapsed.
In Cosby's Razorblade Tears, two fathers avenge their gay sons' murders. One is Black, one is white. Neither was comfortable with his son's sexuality while they were alive. The noir violence gives them a channel for grief they can't otherwise express, and Cosby never lets the reader forget that the violence is also a way of avoiding the harder conversation they should have had years ago.