"In its simplest form the problem is this: God is omnipotent; God is good; and yet evil exists. There seems to be some contradiction between these three premises, so that if any of them were true the third would be false. But at the same time all three are essential parts of most [theist] positions: the [theist], it seems, at once must and cannot consistently adhere to all three." 
"In its simplest form the problem is this: God is omnipotent; God is good; and yet evil exists. There seems to be some contradiction between these three premises, so that if any of them were true the third would be false. But at the same time all three are essential parts of most [theist] positions: the [theist], it seems, at once must and cannot consistently adhere to all three." 
-Mackie, "Evil and omnipotence"