We could put it this way: The shadows prove the sunshine. There can be sunshine without shadows, but there can’t be shadows without sunshine. In other words, there can be good without evil, but there can’t be evil without good; and there can’t be objective good without God. So evil may show there’s a devil out there, but it can’t disprove God. Evil actually boomerangs back to show that God exists. — Frank Turek (from, Why Evil Disproves Atheism)