An Unstoppable Force vs. An Immovable Object: The Dark Knight

I just re-watched this movie tonight with some other members of Baker 3rd in the screening room, and I still can't believe how blown away I am every time I see it. The suspense, the mind games, waiting to see what's behind the next turn - it all just builds up. But one of my favorite subjects to analyze in this movie, more than anything else, is Joker and Batman's rivalry. Most people know that Batman and Joker are mortal enemies, but what really drives them to act as they do? I've read in depth into the history about the two, but I'll keep it within the confines of the film (not that that's a bad thing either). 

Firstly, both were born of a significant event in their lives: it's what drove them to fight for their sides. Batman chose justice and order, while Joker chose anarchy and chaos. We don't know Joker's real origin, but he tells multiple stories throughout the movie. But what's different is that the Joker doesn't have a set of rules, no moralistic code. He uses that against Batman, and thats why he doesn't fear him. Batman will never kill the Joker, no matter how deep the Joker takes him into the lake of blood and guilt that Joker creates. Yet Joker won't kill Batman simply because that would be too easy. If Batman dies, he dies a hero and a symbol to the people. But if the Joker can break Batman's spirit, then he proves the exact opposite of why Batman even began his career; every man has a breaking point. Batman's breaking point would be to kill the Joker, and break his code. That's why they're destined to fight forever, in an unstoppable clash that will last until an outside force ends it.

Second, the Joker is another term for a Jester, or a fool. The alias fits because only someone so insane could act so animated and full of laughter at the problems he sees in this world. Gotham is extremely corrupted, and he knows it. But Joker has a better grip on reality than he wants people to know. For example, in the scene where he is in the hospital with Harvey Dent/Two-Face, he holds the gun in Harvey's hand to his own head, and says something along the lines of "lets introduce a little anarchy, hm?" This is a home-hitting line for what the joker wants to accomplish: bringing Harvey Dent down to his psychotic level, and showing that even the best of men can fall. But, supposedly, the Joker's finger is holding down the hammer of the gun when he lets Harvey choose to kill or spare him. This means that even if Harvey did shoot, nothing would have happened. The hammer wouldn't have triggered the bullet. The Joker doesn't just cause anarchy and chaos, he controls it as a weapon.

Finally, both characters need each other to survive. Joker is the only villain that won't kill Batman simply because he would have no purpose without him. His sole existence is to remove Batman from his incorruptible position above the average man. He wants the challenge, and its likewise for Batman. Bruce dedicates his life to becoming Batman. It consumes him, takes over his entire state of mind. It's his "greater purpose" in life, and he won't stop until he thinks Batman isn't needed anymore. Yet, to him, Batman will always be needed, to stop people like the Joker, and keep the order. So no matter what happens, who wins the fight, there will always be another battle in an endless war.