It can be a bit weighty but stick with me. Both Batman Returns and The Dark Knight were basically about the question of whether Gotham could be saved. Any third Batman movie from Nolan will inevitably also deal with the same question.
Bruce Wayne’s father attempted to try and save Gotham through social aid, by building a metro tying together Gotham. This addressed some of Gotham’s problems, but not the real problem, crime. Organized crime. Batman is the tool that Bruce Wayne chose to use to save Gotham from organized crime.
Ra’s Al Ghul believed that Gotham could not be saved. That it was a source of rot and had to be destroyed. In Batman Returns, Batman stopped Ra’s Al Ghul, fighting for the right to try and save Gotham. In The Dark Knight however Gotham and Bruce Wayne need to be saved from Batman. Bruce Wayne wants to resume a normal life and everyone is hoping that the police and Harvey Dent can step in to restore law and order to Gotham.
In The Dark Knight the question is no longer can Batman save Gotham, it’s clear that he can. The question is can Gotham be ruled by the law. As Ra’s Al Ghul came to challenge the idea that Gotham could be saved, the Joker serves as an agent of chaos, challenging the idea that Gotham can be ruled by the law.
The Joker’s tactics are multifold, first in his games with criminals and ordinary people, he seeks to prove that given a choice, people can be predictably programmed to turn on and kill each other without following any moral code. He also seeks to prove that any enforcers and keepers of the law, whether it’s Batman or Dent or the police detective he’s locked in with, can just as easily be forced to break the law, proving once again that there is no moral order, either from the top down, or the bottom up.
The thrust of the Joker’s argument to Dent is that there is no morality because people are not moral. Something Dent himself already believes by that point. Those who administer the law are in the end just as broken as those who are subject to it. The only morality therefore is the morality of chance. When you subtract the idea that there can be any kind of formal moral order, right and wrong don’t enter into it, and the only chance for either justice or right, is pure chance. This is the basic argument of chaos and anarchy, if order is biased toward selfish human choices that are immoral, then the amorality of chance is preferable.
By refusing to be corrupted Batman denies the Joker his ultimate victory, but leaves Gotham dependent on him for law and forces a coverup that turns him into the enemy of the law, giving the Joker a smaller subtler victory. Gotham can still be saved, but Batman is still the only one who can do it. Law enforcement has proven that it can’t step up. That leaves Gotham with a Dark Knight, an outsider who must do what Gotham itself can’t.
Now where does a third Batman movie from Nolan go from here? If the first movie asked can Gotham be saved and the second movie asked if Gotham could be saved under its own law and order, the third movie might ask whether Gotham will ever need to be saved from Batman or whether Gotham itself can save Batman.
The ending of The Dark Knight was inevitable, because Batman exists because the police and the prosecutors office can’t handle it alone. The third movie will have to go into more uncharted territory, asking about the soul of Batman and the soul of Gotham and how both will find their balance in their unique relationship.