Each of the film noir movies that I watched--The Maltese Falcon, Touch of Evil, Chinatown, and Shadow of a Doubt--have certain similarities that cause them to all fall under the title of film noir, however some of them do seem to be variations on film noir. The Maltese Falcon and Touch of Evil seem to be essential film noir; they both were created during the height of film noir which may be part of the reason why. Both movies have the hero private investigator character--Sam Spade in The Maltese Falcon and Mike Vargas in Touch of Evil--who is rather cynical and disconnected with the actual police force. Both of these characters are out to solve some sort of crime mystery--Spade has multiple murders and a strange prized falcon that he is investigating and Vargas is on the trail of a murder when he discovers other corruption that he must get to the bottom of.
The Maltese Falcon and Touch of Evil also have similar settings because both take place in cities and there is lots of darkness and shadows throughout. Both of these films also have the underlying belief that the government run police force is no good and it is up to the outside investigator--Spade as a private eye and Vargas because he is from Mexico--to solve everything and put an end to corruption. There is a suspenseful tone throughout the movies and many of the characters often switch from good to bad and visa versa and there is a strong sense of moral ambiguity. For example in The Maltese Falcon the femme fatal character Brigid O'Shaughnessy switches from being credible to non-credible throughout the film, and in Touch of Evil Captain Quinlan seems reliable at first but then we find out that he has been planting evidence.
The other two films that I watched, Chinatown and Shadow of a Doubt, had some of the same elements as The Maltese Falcon and Touch of Evil, but also seemed to vary from the other films. They both also have some characters that seem to switch from good to bad like Uncle Charlie in Shadow of a Doubt and Evelyn Mulwray in Chinatown. However in these films there is not a direct conflict with the police like there is in the other two films. In Chinatown Gittes does conflict with the government, but he is not really racing against them to solve the crime and in Shadow of a Doubt there is no conflict with other investigators or the government. I think Chinatown is more noir than Shadow of a Doubt because it does have a typical femme fetal character with Mrs. Mulwray and it has a cynical private eye who ends up solving the mystery.
Shadow of a Doubt is a twist on film noir because there are detectives in the film, but they are just minor characters rather than the hero of the movie. The hero in the movie is a female because Young Charlie is the one who discovers the truth about her uncle, but she is also a lot like a femme fatal character because since she knows the truth she can be detrimental to Uncle Charlie and in the end she actually is. Both Shadow of a Doubt and Chinatown have the moral ambiguity and suspenseful tone of film noir, but they do not have as shadowy and urban look as Chinatown and The Maltese Falcon. I think part of this lack of film noir look in Chinatown is due to the fact that it is in color because that takes away from the dramatic effect of the shadows. Shadow of a Doubt takes place in a small town rather than an urban environment because Uncle Charlie leaves the city to go there and everyone seems to know everybody in that town. These films are still noir, but seem to be modified versions of noir.
