Then you will know the truth, and the truth shall set you free – John 8:32
During his first meeting with Noah Cross, Jake Gittes is insulted by the older man and gets up to leave. Cross tells him to sit back down, saying that “You [Gittes] may think you know what you’re dealing with, but believe me, you don’t.” Jake smiles, laughs, and tells Cross that “that’s what the district attorney used to tell me in Chinatown.”
For Noir protagonists, truth is primary. Young Charlie kills her uncle in her search for the truth, Holly Martin kills his friend. Mike Hammer is shown a type of truth by Christina in Kiss Me Deadly, and spends the rest of the movie searching after it. Johnny, in Gilda, knows the truth about Gilda, and becomes obsessed with keeping it from Ballin. Even Walter Neff, our weak male protagonist par excellence, puts telling the truth of higher importance that escaping to mexico.
In Chinatown, Jake Gittes is no different. Certainly he is motivated by his reputation, and eventually by his feelings for Evelyn, but his primary mover is the desire for the truth. For instance, in the scene in which the truth of Katherine’s parentage is revealed, Gittes is almost manic in his slapping of Evelyn. He does suspect her of murder, but what motivates him in his violence is primal, deeper than betrayal.
Judging by the moral and philosophical influences and themes of noir, the protagonist’s search for truth is symbolic of the search for a Truth with a capital T. The search for meaning, a cause, an unmoved mover. The protagonists, in searching out crime and evil, are searching out a reason for this evil, a justification or retribution for it. In The Third Man, Holly takes his stand against the nihilism of Harry Lime, just as young Charlie does in Shadow of a Doubt. In these classical noir’s, the capital-T-truth, while not proven, is at least hinted towards: Harry and Old Charlie pay for their crimes and the perspective on the world is re-aligned along the lines of conventional morality.
Not so in Chinatown. It may be a result of the defunct production code, but Jake’s search for Truth is the first to end in absolute despair. The woman he loves is dead, her daughter in the hands of a incestuous rapist. The city is going to die of thirst, and the people who can save it are instead choosing to stuff their wallets. Even the most basic of elements, water, seems evil; it kills two men in the film. When cross says that Gittes doesn’t know what he is “dealing with,” Cross is talking about the capital T-truth; Gittes believes he will uncover a decent world, one in which the muderer will be revealed and appropriately punished. However, this is not what he finds; the real world is one in which the murderer wins, and corruption is intrinsic. The capital-T-truth Gittes uncovers is that his opinion on Chinatown is not indicative Chinatown, but of all of Los Angeles. And in that way, Chinatown is the darkest movie we’ve seen, despite taking place in such a sunny place.