Chinatown can be given many themes but one theme that dominates is of the common people in the hands of evil and the steady corruption of America's government. There are several scenes in the movie that can support the theme. In the movie, Jack Gittes, a specialist in divorce investigation, symbolizes the drift from the corruption of government and also the hope that lies in the hands of the common people. In the plot the common people are represented by the population of Los Angeles and the San Fernando Valley whom are fighting in the times of a drought for water to drink and to fertilize farm land. Noah Cross, the secret villain, masterminds corruption on the water utilities in his favor to add to his already bottomless money-scrubbing pockets, despite the crimes and suffering conflicted on the common people.

As a motif, ignorance helps support the movies main theme of the non-stoppable corruption that foreshadows the city, and Jake's replication of the haunting past. In the movie, Jake's lack to "read the signs" causes him to remain one step behind in his quest for salvation, ultimately resulting in failure. When Jake first arrives at the Mulwray mansion he discovers a saltwater pond in the backyard where a servant mumbles,"bad for the grass" which he refers to the grass dying from the inability to adapt to the harsh saltwater from the pond. At the same time he notices something shiny in the water that remains a clue to be discovered later. Because Jake ignores the clues that he is supposed to discover, he fails to complete his duties in his feeble attempt to crack the case. Throughout the movie, the film never allows the viewer to discover more than any of the main character's are able to discover, allowing the viewers to experience the reason for the main character's ignorance. This also allows for a more shocking and unpredictable climax and overall storyline.