As opposed to a theodicy (a justification for God’s actions), Plantinga puts forth a defense, offering a new proposition that is intended to demonstrate that it is logically possible for an omnibenevolent, omnipotent and omniscient God to create a world that contains moral evil. Significantly, Plantinga does not need to assert that his new proposition is true, merely that it is logically valid. In this way Plantinga’s approach differs from that of a traditional theodicy, which would strive to show not just that the new propositions are sound, but that they are also either true, prima facie plausible, or that there are good grounds for making them. Thus the burden of proof on Plantinga is lessened, and yet his approach may still serve as a defense against the claim by Mackie that the simultaneous existence of evil and an omnipotent and omnibenevolent God is “positively irrational”.
As Plantinga summarised his defense:
Plantinga’s argument is that even though God is omnipotent, it is possible that it was not in his power to create a world containing moral good but no moral evil; therefore, there is no logical inconsistency involved when God, although wholly good, creates a world of free creatures who chose to do evil. The argument relies on the following propositions:
- There are possible worlds that even an omnipotent being can not actualize.
- A world with morally free creatures producing only moral good is such a world.
Plantinga refers to the first statement as “Leibniz’s lapse” as the opposite was assumed by Leibniz.The second proposition is more contentious. Plantinga rejects the compatibilist notion of freedom whereby God could directly cause agents to only do good without sacrificing their freedom. Although it would contradict a creature’s freedom if God were to cause, or in Plantinga’s terms strongly actualize, a world where creatures only do good, an omniscient God would still know the circumstances under which creatures would go wrong. Thus, God could avoid creating such circumstances, thereby weakly actualizing a world with only moral good. Plantinga’s crucial argument is that this possibility may not be available to God because all possible morally free creatures suffer from “transworld depravity”.
Plantinga’s idea of weakly actualizing a world can be viewed as having God actualizing a subset of the world, letting the free choices of creatures complete the world. Therefore, it is certainly possible that a person completes the world by only making morally good choices; that is, there exist possible worlds where a person freely chooses to do no moral evil. However, it may be the case that for each such world, there is some morally significant choice that this person would do differently if these circumstances were to occur in the actual world. In other words, each such possible world contains a world segment, meaning everything about that world up to the point where the person must make that critical choice, such that if that segment was part of the actual world, the person would instead go wrong in completing that world. Formally, transworld depravityis defined as follows:
Less formally: Consider all possible (not actual) worlds in which you always choose the right. In all those, there will be a subpart of the world that says you were free to choose a certain right or wrong action, but does not say whether you chose it. If that subpart were actual (in the real world), then you’d chose the wrong.
Plantinga says that “What is important about the idea of transworld depravity is that if a person suffers from it, then it wasn’t within God’s power to actualize any world in which that person is significantly free but does no wrong—that is, a world in which he produces moral good but no moral evil” and that it is logically possible that every person suffers from transworld depravity.