The Free Will Defence

The Free Will Defence

The free will defence is widely regarded as the most successful philosophical response to the logical problem of evil. Developed primarily by the American philosopher Alvin Plantinga (b. 1932), the free will defence does not attempt to explain why God permits evil (that would be a theodicy). Instead, it has the more modest aim of showing that the existence of God and the existence of evil are logically compatible — that there is no formal contradiction in affirming both. Plantinga’s defence, presented in God, Freedom, and Evil (1974) and The Nature of Necessity (1974), employs the technical apparatus of modal logic and possible worlds semantics to achieve this goal.

The Core Argument

Recall Mackie’s inconsistent triad: (1) God is omnipotent, (2) God is wholly good, (3) evil exists. Mackie argued that these three propositions are logically inconsistent. Plantinga’s strategy is to show that they are not inconsistent by identifying a proposition that is possibly true and that, if true, would render all three propositions compatible.

Plantinga’s key move is to challenge Mackie’s connecting principle that an omnipotent being can create any logically possible state of affairs. Plantinga argues that even an omnipotent God cannot do the logically impossible: God cannot create a round square, God cannot make 2 + 2 = 5, and — crucially — God cannot create free beings who are guaranteed to always freely choose the good.

• If God creates beings with genuine libertarian free will — the ability to choose between alternatives without being causally determined — then it is logically impossible for God to guarantee that they will always choose the good
• A world containing creatures who are genuinely free is more valuable than a world of automata who are programmed to do good but have no real choice
• It is therefore possible that God, in creating free creatures, could not have prevented them from sometimes choosing evil
• If this is even possibly true, then God and evil are logically compatible, and Mackie’s argument fails

Possible Worlds

Plantinga’s argument makes extensive use of possible worlds semantics — the philosophical framework in which we analyse modal claims (claims about possibility and necessity) by considering different possible ways the world might have been. A “possible world” is a complete, consistent description of how reality might have been. The actual world is one of infinitely many possible worlds.

Key concepts include:

• A proposition is possibly true if there is at least one possible world in which it is true
• A proposition is necessarily true if it is true in all possible worlds
• A proposition is contingently true if it is true in the actual world but false in some other possible world

Plantinga uses this framework to argue that God’s omnipotence does not extend to actualising just any possible world. Some possible worlds contain free creatures, and the actions of free creatures are not within God’s direct control. God can create the conditions for free action, but God cannot determine the outcomes of free choices without destroying freedom.

Transworld Depravity

Plantinga introduces the concept of transworld depravity to strengthen his defence. A person suffers from transworld depravity if, in every possible world in which that person exists and is free, they would go wrong with respect to at least one morally significant action — that is, they would freely choose to do something wrong at least once.

Plantinga argues that it is logically possible (though not necessarily actual) that every possible free creature suffers from transworld depravity. If this were the case, then no matter which free creatures God chose to create, and no matter what circumstances God placed them in, they would freely choose to do at least some evil. God could not have created a world containing free creatures and no evil, because the creatures themselves would inevitably misuse their freedom.