Ni: Harvey Dent has a singular mission, which he devotes his life and time to fulfilling. He would never leave anything up to chance, though he likes to pretend that he does, but rather, does everything with a purpose and a specific end in mind. He has a strong grasp of irony and symbolism, enough to refuse skin grafts so that he can adopt that name that others once called him: two face (not to mention, the double headed coin he messes around with).
Te: Harvey doesn’t just talk. He does. He not only comes up with a vision, he does everything in his power to implement it. When captured, he does not sit and accept his death. He tries to escape. He’s direct in his speech and calculating in his decisions.
Fi: Nothing anyone else can say or do can have any affect on Harvey’s resolves, or emotions. Harvey lives by an internal moral code, which he does not violate under any circumstances (that is, until he loses the one person he cares about and basically flips into insanity). His vengeance is motivated solely by his suffering and wants to inflict the same pain on those who hurt him.
Se: When his world is turned upside down, Harvey Dent turns upside down. He changes from a calculating, man of precision and principle, to a reckless, impulsive and moral-less madman. Instead of planning before hand, he begins making reckless, impulsive decisions that lead to many deaths including his own.