What is the main theme of The Dark Knight?

The Dark Knight, in my view, is an epic description of the Joker's character. There is no other theme to the movie. Just as 'Batman Begins' was centered mainly around the characterization of the Batman. I observed a similarity and a difference between the Joker and the other mob bosses/bad guys.

The similarity is that, both the bad guys and Joker have anti-social ideas. The difference lies in what level of sophistication the players employ. The other guys want to kill Batman and prey on the fearful. Joker is different. He just wants to kill everyone else. He also wants to prove that everyone is inherently un-altruistic / sadistic. That is why he conducts the experiment on the ferry with the prisoners and the convicts. This is classic prisoners' dilemma.

He also succeeds in employing Harvey Dent, the supposed hope of Gotham City, the only DA brave enough to prosecute Gotham's criminals, and turn him against Gotham. These are a battery of experiments that he performs - just for the thrill of finding out what happens.

During the climax of the movie, there is a dialogue - "Sometimes truth is not good enough. Sometimes people deserve more. They deserve to have their faith rewarded". While these dialogues are presented, we see two scenes.

1. Alfred burning the letter that Rachel gave to Bruce. Here, Bruce believes that Rachel was going to wait for him but that's not the truth and if revealed, it can break Bruce. So, Alfred hides the truth.

2. Batman asks Gordon to say that Batman killed Harvey because they can not let Joker win. So the truth is that Joker was successful in shaking up Gotham. He indeed took the best man and turned him bad. But Batman & Gordon hide this truth so that the people of Gotham don't lose their faith.

This, according to me, is the main theme of the movie.

In addition to the already existing good answers, another theme of the movie, with a strong connection to current political and social problems, is of course terrorism.

Especially how to deal with people (or one man in this case) who are not driven by "ordinary" criminal motives (like money) and don't react to the threats of "ordinary" punishment (like imprisonment or death), how easy it is for them to push an organized society (that is just not prepared for such an irrational person) into chaos and, most important, how far the society's executive organs (in this case the Batman) would go (or what he needs to become himself) to stop such a person.

This culminates in Batman building the perfect surveillance state (with those unrealistic cell-phone radars). Although he is smart or honest enough to destroy this machine once he's found the Joker, he has obviously crossed a line there.

To conclude, I think it is hard to find one single theme to describe the movie, as it contains many interresting themes. And I would say Nolan himself (he wrote it, didn't he?) didn't have one single theme in mind to center the story around.

This is an old thread and I assume you've already turned in your paper, but it's an interesting question so I wanted to share an answer.

Like many good movies, The Dark Knight has several themes, but to me the primary theme of the movie is duty. The reason why I say this is because the primary conflicts of the film are centered around that theme:

1. Joker - he explained to Harvey that he was a dog chasing cars, that he didn't really have much of a plan but that he just wanted to induce a little carnage. He enjoyed his duty, but the thing that motivated him - that got him to keep going after Batman - was that he felt a duty to disrupt, to shake up, to change, to show people what they were really made of.

2. Batman - duty incarnate. He is scarred, physically and mentally and does not want to keep doing this job but the city needs him. He could have, and wanted to, kill the Joker, but chose not to because he duty is to uphold the law, not become the law. And after Harvey's death, he takes responsibility. Commissioner Gordon's speech over the closing credits sums up Batman about as perfectly as anything I've ever seen written about him does.

3. Harvey Dent - Harvey was pulled into politics by Bruce Wayne, who told him it was his duty to protect the people of Gotham City. And when he lost Maggie Gyllenhall's character, he went insane but at the core of that insanity was still duty -- to represent the arbitratiness of the world.

4. Lucius - Lucius set up the cell phone monitors for Bruce Wayne not because he wanted to, but because he felt a duty to Bruce to help him stop the Joker.

5. Inspector Gordon - hid the details of his death from his wife to serve the greater duty of catching the Joker.

6. Bank robbers - each did their assigned task, progressively executing each other, even though at some point no one asked (until it was dramatically appropriate) why if they had orders to kill another robber, it stood to reason that another robber had orders to kill them.

7. Boat bombs - another examination of duty and responsibility. The people on the boats had the duty to save themselves, but Tiny Lister transcended that to show that even duty can have too high of a cost, and that's why he threw the detonator out of the window.

In that sense, 6 and 7 are evolution points of the script in that 6 is about what happens when someone blindly does their duty and 7 is about when someone refuses to do a duty to serve a higher purpose. IMHO, anyway.

And now I have done my duty, which was to provide an answer to this question, so I am finis.