Complex sentence: An amoral person denies the existence of morality, as opposed to an immoral person who violates a certain moral code, but may still believe in the underlying truth of that moral code.
Split into simpler sentences: An amoral person denies the existence of morality, whereas an immoral person recognizes the existence of morality but chooses not to recognize it as binding or intentionally defies it. An immoral person who violates a certain moral code may still believe in the underlying truth of that moral code.