Out of the Past is often described as one of the best examples of film noir, representing its various themes and embodying its very title with its investigation of the darkest sides of human nature. The film satisfies nearly all of our preconceived notions of what film noir "should" be: we are given a protagonist whose shrouded past is revealed and gradually comes back to haunt him, as well as a dangerously cunning femme fatale who encapsulates every stereotypical quality that a good Delilah should. There are love triangles and deception, as well as no small helping of violence and crime. The film brings out many of humanity's worst qualities and exploits them for the purpose of showing the viewer what a dark place the world can be. The viewer is left with both an unsettling sense that the depths of man's being are filled with an enormous potential for evil, as well as the uncomfortable notion that the events of the past that we thought were left behind may return at any moment to chip away at the life we lead.
The use of lighting, costumes, and shadow imagery also serve to effectively reinforce the darker themes of the plot. The entire film seems to be shrouded in the mists of secrecy and deceit, and this offers the viewer no hope that a happy ending awaits these characters. Additionally, the use of flashback provides an ironic twist for the viewer, who knows as well as Jeff that the woman he is falling in love with is going to betray him at every possible turn. The director almost seems to taunt Jeff by dressing Kathie in white during their first encounter. It is clear that she could not be farther from pure and innocent, and the viewer can see how Jeff has been deceived by every aspect of herself that she presents to him. Equally, the director allows us to see early on that Jeff is going to become entangled once again in her web of manipulation and cruelty. In his work entitled "Notes on Film Noir", Paul Schrader points out that Jeff Bailey "relates his history with such pathetic relish that it is obvious there is not hope for any future: one can only take pleasure in reliving a doomed past." The film does not imply that the notion that the past is inescapable is a happy one - rather, it illustrates the way that it will force Jeff on a path that ultimately leads to his destruction.
Despite the fact that Out of the Past seems to embody many of the commonly accepted features of film noir, it does not leave the viewer with the ability to accurately define this category of films. There are other examples of film noir that do not include the private detective or the duplicitous femme fatale. Indeed, there is very little continuity in the specifics of the many different examples of film noir. This raises the challenges of terming film noir as a genre in and of itself. It is not defined by setting, as are Western films, or by a common procedure by which all the films are developed and play out. Rather, it seems better defined as a way of classifying humanity and considering the world around us. Film noir does not rely on a specific type of plot or distinct "categories" of characters or particular cinematographic techniques that appear over and over again. It merely emphasizes the darkest aspects of common human emotions and behavior, and perverts those basic qualities in a way that leaves the viewer wondering if this depravity may lie within us all.