C.S. Lewis om vondskap og dualisme:
To be bad, he must exist and have intelligence and will. But existence, intelligence and will are in themselves good. Therefore he must be getting them from the Good Power: even to be bad he must borrow or steal from his opponent. And do you now begin to see why Christianity has always said that the devil is a fallen angel? That is not a mere story for the children. It is a real recognition of the fact that evil is a parasite, not an original thing. The powers which enable evil to carry on are powers given it by goodness. All the things which enable a bad man to be effectively bad are in themselves good things—resolution, cleverness, good looks, existence itself. That is why Dualism, in a strict sense, will not work.
— Mere Christianity (s. 45)