What is Plantinga's free will defense, and does it succeed in solving the logical problem of evil?

Alvin Plantinga's Free Will Defense is one of the most important developments in contemporary philosophy of religion, having fundamentally changed the course of philosophical discussion about the problem of evil. Understanding it precisely requires distinguishing between the logical and evidential problems of evil, and grasping the logical tools that Plantinga employed.

Inadequate Responses to Avoid

From some believers:

"Plantinga proved that God exists despite evil." This misunderstands the project. Plantinga did not attempt to prove God's existence, but rather to refute the claim that the existence of evil logically contradicts the existence of a perfect God. A defense differs from a theodicy.

"Free will justifies all evils." This exceeds the argument's limits. Plantinga's defense deals with moral evil (resulting from human actions), not directly with natural evil (earthquakes, diseases). Moreover, it does not claim that free will justifies all evil, but rather that it makes the existence of some evil logically possible.

From some critics:

"Plantinga relies on a false metaphysics of free will." This is a legitimate criticism but misses the target. Plantinga does not need to prove that libertarian freedom actually exists, but only that it is logically possible. Logical possibility suffices to refute logical contradiction.

"The evidential problem of evil remains." True, but this is not an objection to Plantinga. He did not claim to solve the evidential problem (the quantity and distribution of evil), but only the logical problem.

Why These Responses Are Inadequate

They fail to understand the precise nature of Plantinga's logical project, the limits of what he attempts to prove, and the difference between different types of arguments in philosophy of religion.

The Logical Problem of Evil: Mackie's Formulation

J.L. Mackie clearly formulated the logical problem in 1955:

1. God is omnipotent
2. God is omnibenevolent
3. Evil exists

These three propositions—according to Mackie—are logically contradictory. An omnipotent God can prevent evil, and an omnibenevolent God wants to prevent evil, so how can evil exist?

Mackie added two implicit premises to clarify the contradiction:

4. An omnibenevolent being prevents evil as far as it can
5. There are no limits to what an omnipotent being can do

Therefore: God must prevent all evil, but evil exists, so God (with these attributes) does not exist.

Plantinga's Strategy: Defense, Not Theodicy

Plantinga distinguished between two types of response:

- Theodicy: An attempt to explain why God actually permits evil
- Defense: An attempt to prove that the existence of God and evil is logically possible

Plantinga chose defense, which is weaker and easier. He does not need to prove the actual reason for evil's existence, but only to prove the logical possibility of God and evil coexisting.

Libertarian Free Will

The core of Plantinga's defense is the concept of libertarian freedom:

- An action is free in the libertarian sense if the agent could genuinely have chosen otherwise in the same circumstances
- This differs from compatibilist freedom, which accepts determinism

Plantinga says: Let us suppose (for argument's sake) that libertarian freedom:
1. Is logically possible
2. Is a great good worth creating
3. Requires the possibility of doing evil

If these assumptions are logically possible, then the existence of God and evil is logically possible together.

The Central Argument

1. A world with free creatures (in the libertarian sense) is better than a world without freedom
2. God cannot create free creatures programmed to do only good (logical contradiction)
3. Therefore: Creating a world with freedom requires accepting the possibility of evil
4. Some free creatures actually chose to do evil
5. Therefore: The existence of evil is logically compatible with the existence of a perfect God

The Concept of "Transworld Depravity"

Plantinga developed an important technical concept: What if it were logically possible that all possible free creatures would choose to do some evil in any possible world in which they were created?

This does not mean creatures are "programmed" for evil, but that God (through His middle knowledge) knows that every possible free creature would freely choose to do some evil.

If this is logically possible, then God faces a choice:
- A world without free creatures (and without the good resulting from freedom)
- A world with free creatures (with some resulting evil)

Choosing the latter might be compatible with divine perfection.

Extending the Defense to Natural Evil

Plantinga suggested that the defense can be extended to natural evil in two ways:

1. The spiritual beings hypothesis: Perhaps there exist free spiritual beings (demons) that cause natural evils. This is not a claim that this actually happens, but that it is logically possible.

2. Natural evil as consequence of sin: Perhaps natural evil is an indirect result of the misuse of freedom (as in the story of the Fall).

Again, the goal is not to prove these hypotheses correct, but their logical possibility.

The Philosophical Response

Most philosophers today acknowledge that Plantinga succeeded in refuting the logical problem of evil as formulated by Mackie. Even Mackie himself later admitted the strength of Plantinga's defense. William Rowe, one of the most prominent defenders of the argument from evil, wrote: "It can be said with confidence that the logical problem of evil is dead."

Main Criticisms

1. Metaphysical assumptions: The defense depends on the possibility of libertarian freedom, which is controversial. But Plantinga only needs logical possibility, not actuality.

2. Middle knowledge: The concept of "transworld depravity" depends on Molinist middle knowledge, which is controversial. But again, logical possibility suffices.

3. Does not solve the evidential problem: The quantity and distribution of evil remain problematic. Plantinga's defense does not explain why all this horrific evil exists.

Final Assessment

Plantinga's defense is considered successful in its limited goal: refuting the claim that the existence of God and evil are logically contradictory. This is an important philosophical achievement that changed the direction of debate.

But it does not solve the problem of evil completely. The evidential problem (does the existence of this amount of evil make God's existence improbable?) remains open and requires different treatment.

The balanced position—according to the method of "rational probability" (rajḥān ʿaqlī)—is to acknowledge Plantinga's success in his limited project, while recognizing that the problem of evil remains a serious challenge requiring additional responses (theodicies, not just defenses).

For Advanced Reading

- Advanced level: Middle knowledge and the problem of evil among contemporary Molinists
- Advanced level: Robert Adams' critique of middle knowledge and its impact on Plantinga's defense
- Alvin Plantinga, God, Freedom, and Evil (1974)
- Alvin Plantinga, The Nature of Necessity (1974), Chapter IX
- "The Logical Problem of Evil" page on the website