evil, antithesis of good. The philosophical problem of evil is most simply stated in the question, why does evil exist in the world? Death, disease, and sin are often included in the problem. Traditional Christian belief ascribes evil to the misdeeds of humans, to whom God has granted free will. The Christian systems that believe in predestination and justification by faith claim, like their Christian opponents, that God is still not the author of the evil men do. One explanation of evil is dualism, as in Zoroastrianism and Manichaeism. In optimism evil is treated often as more apparent than real. The book of Job is a literary treatment of the problem.