I’m watching lot of film noir lately, from the 1940s (the style persisted through the 1950s, so there’s much more to be seen), and wondering about noir in general. What is “pure” film noir? Why is film noir so enduringly popular?

I answer my first question easily, though I suspect hardly to anyone else’s content, because I think characters and world-view—but not, as with westerns, highly particular settings—are more important to noir than cinematic style.

A pure film noir is about little guys and gals getting a raw deal in a world that never gives them an even chance. Noir protagonists are meager many respects. They have no money, not much talent, scant intelligence, little self-control. Passions they do have, of course, and those exacerbate their deficiencies, though they sometimes make them capable of love and sacrifice, too. Their raw deal consists of being unemployed, badly employed, or criminally employed; living in dumpy rented rooms and cheap houses; and thinking that looking sharp and hard is looking consequential. As for their world, there’s no one virtuous in it; maybe there’s no virtue in it. In such an atmosphere, sin is unavoidable, and when a noir protagonist receives the reward for his sins—death—his and his survivors’ only consolation lies in knowing that he’s conferred the same reward on at least one of those who sinned against him—that is, if he has.

Noir’s technical ingredients—snappy, heartless dialogue, pervasive rudeness and sudden violence, high-contrast cinematography of interiors and night scenes, semi-jazzy or heavy-breathing music seasoned with dissonance, lots of glowering by the actors—are all highly welcome complements to its hopeless-little-guy-in-a-bad-world ur-text, and all are dispensable, though probably not all in one film.

The noir template is literary, traceable to literature, most proximately the stuff called pulp fiction, which no lesser lion than Ernest Hemingway tried writing, not very well at all, in the stories about Harry Morgan collected as To Have and Have Not and bearing scant resemblance to the movie of that name, the first (non-noir, by my lights) of at least three screen adaptations.

The real, not-quite-pulp father of noir is James M. Cain, two of whose stories, The Postman Always Rings Twice (as it happens, the first adult novel I read, at age 12) and Double Indemnity, were best adapted into films by, respectively, Luchino Visconti (as Ossessione, 1943) and Billy Wilder. Genuinely noir, both are about dopes with overactive glands, who murder for money as well as “love” and meet their just deserts.

Forefathers hover behind Cain. A trained singer, he certainly knew Bizet’s Carmen, the basis of which, Prosper Mérimée’s 1847 story, is twistedly romantic, at best, and much grittier than the opera. What’s more, Cain acknowledged Émile Zola as an influence, and the dopes-in-heat set-up of Cain’s classics is a dead steal from Thérèse Racquin (1867). I know of a third great literary proto-noir, Nikolai Leskov’s horrific “The Lady Macbeth of the Mtsensk District” (1865), the basis of Shostakovich’s most famous opera and also the disturbingly good movie, Siberian Lady Macbeth (1962), by the Polish filmmaker, Andrzej Wajda. Whether Cain knew Leskov’s tale, I can’t say; it’s unlikely he knew Shostakovich’s opera before he wrote Postman, which was published in the year, 1934, of the opera’s premier, half the world away.

Among cinematic prototypes, You Only Live Once (1937), arguably Fritz Lang’s best American film, is Mount Everest. It’s a Bonnie-and-Clyde variation about a superficial innocent whose criminality stems from resentment and irresponsibility and the foolish public defender’s assistant who falls for him. Almost everybody else in the film is fully as corrupt; the most upright character, that public defender, is a heart-on-sleeve, society-blaming, liberal sap who’s ultimately prepared to bend the law to suit his ideology. Very violent and shockingly “cynical” for its time, You Only Live Once profits from the visual expressionism Lang brought with him from Germany; plenty of shots are emotionally tinged by fog, shadows, and odd angles of regard. It was a box-office bomb, but I regard it as the premonitory quintessence of film noir.

The purest noirs I’ve seen so far are Double Indemnity (1944), Detour (1945), Decoy (1946), and Raw Deal (1948). The first is an A picture from Paramount, one of the major golden-age-Hollywood studios; the others are products of so-called poverty row studios PRC, Monogram, and Eagle-Lion, respectively. Double Indemnity is a class act that boasts big-name actors. Raw Deal (the best title in all film noir) looks the most noirish of these four, a stream of high-contrast, constructivist images, thanks to the archetypal noir craftsmen who made it, director Anthony Mann and cinematographer John Alton. It’s about an escaped convict—bent on vengeance against the gangster who framed him—and the two women stuck on him. Each shot in less than a fortnight and looking it, Detour and Decoy are powered by monstrous femmes fatales, ruthlessly played in the marginally classier Detour by Ann Savage, who enjoyed a minor career thereafter, and in Decoy by Jean Gillie, who didn’t (she died in 1949).

If you’ve seen these classic noirs and enjoyed them (how could you not?), ask yourself why. After all, they’re outrageous to all decency and varyingly credible in incident and human character—Double Indemnity the most likely, Decoy the least. And the hopeless, constricted, amoral if not immoral world they’re set in is a lie, certainly by Christian lights and probably from every other religion’s perspective, too. Even the secular (formerly secular humanists) maintain there is virtue—er, ethical behavior—and that a good life is possible.

And noir’s lasting appeal? To the extent that noir protagonists are unsympathetic—and in the four purest films noir, that extent is considerable—noir affords exquisite schadenfreude. We want these petty monsters to get their comeuppances. And if, like Walter Neff (Fred MacMurray), the insurance salesman lured by lush Phyllis Dietrichson (Barbara Stanwyck) in Double Indemnity, one of the leads retains some of our sympathy, it isn’t because of any there-but-for-fortune-go-I sentiment of ours but rather from feeling that, though we can appreciate being that gamy, at least we’re not that dumb.

Going a little further, apart from and beyond sympathizing, we may identify with even the sorriest noir protagonists, going along with them as they mess up their and others’ lives, sharing their actions and reactions as fully as possible. The vast preponderance of us eventually recoil from such identification, repeatedly as we watch. We’re not really like that, and it’s nice to have that confirmed.