1. God is essentially both omnibenevolent and omnipotent.
2. Evil exists in the world.
3. God is able to prevent evil, but is not willing to do so;
4. Then God is not omnibenevolent.
5. God is willing to prevent evil, but is not able to do so;
6. Then God is not omnipotent.
7. God is either omnibenevolent or omnipotent (from 3, 4, 5, 6).
8. God is not both omnibenevolent or omnipotent (contra 1).
Epicurus (341-270 BCE), Greek philosopher and founder of the school of philosophy called Epicureanism