The aim of Mackie’s paper is to show that the claim that (a): an omnipotent, omniscient, perfectly good God exists is logically inconsistent with the claim that evil exists in the world. He address the logical problem of evil.
The theist affirms, on the one hand, that there is a God who is both omnipotent and wholly good and, on the other hand, that there is evil in the world. Using quasi-logical rules – e.g., an omnipotent being has the power to eliminate evil, an omniscient being knows how to eliminate evil, and that a wholly good being has an obligation to eliminate evil – a logical contradiction becomes apparent in claim (a). If God has the power, knowledge, and obligation to eliminate evil, then evil should not exist. In order for the theist to claim (a), the theist must modify at least one of the constituent propositions in such a way that would seriously jeopardize the essential core of the claim. Therefore, it is not possible both that God is omnipotent and that God was unable to create a universe containing moral good but no moral evil.
A way to challenge Mackie’s argument would have to show that it is logically possible for an omnipotent, omniscient, omni-benevolent being and evil to exist. Mackie’s argument seems to presuppose that a creator is responsible for whatever defects his creation may contain. These defects include the moral failings of creatures the creator created. It may be possible that God is omnipotent and it was not in his power to create a world containing moral good but no moral evil. In other words, there are states of affairs that are possible in themselves but that are not possible for God to create. The creatures that inhabit the world, then, are free to choose to do evil. The action is up to the individual to decide, not God. Although it is possible for all persons to freely do what is right, it is not a state of affairs within God’s power to create. Thus, God cannot be held responsible for the actions of creatures with free will. There is no longer a logical inconsistency between the constituent statements.
Such a challenge tries to demonstrate that a creature’s free will is not compatible with the Creator’s ability to create the world. It could be the case that the Creator can determine the actions of creatures, in spite of the fact that the creature had a choice to do either action A or action B (compatibilism). Mackie could then conclude that it is possible for God to have created a world in which creatures always choose to perform right actions. Therefore, the logical inconsistency still exists for the theist.