The ancient philosophers defined evil in terms of “negation” and “privation.” That is, evil is the negation of the good and a privation (or lack) of goodness. Something that falls short of the plentitude of righteousness is evil. The philosophers were showing that the only way we can describe and define evil is in negative terms. This means that evil, by its very nature, is parasitic. It depends upon its host for its existence. This is what Augustine had in mind when he said that only something good can do that which is evil because the evil requires volition, intelligence, and a moral sense
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