What is the difference between the logical problem of evil (Mackie) and the evidential problem (Rowe), and why did the philosophical discussion shift from the former to the latter?

The distinction between the logical and evidential problems of evil represents one of the most important developments in contemporary philosophy of religion. This distinction completely changed the trajectory of philosophical discussion about evil and God, and understanding it is necessary for tracking contemporary debate on this fundamental issue.

Inadequate responses to avoid

From some believers:

"The two problems are essentially identical, the difference is merely semantic." This is a serious methodological error. The difference between the two problems is fundamental: one claims absolute logical contradiction, the other claims only improbability. Failure to distinguish between them results in responses that confuse different levels of argumentative strength.

"Since the logical problem has been refuted, the problem of evil is finished." This is a hasty conclusion. Solving the logical problem does not mean solving the entire problem of evil. The evidential problem is logically weaker but more intuitively compelling, and it continues to pose a serious challenge to theistic belief.

From some naturalists:

"The shift from logical to evidential is merely a tactical retreat." This is a misleading oversimplification. The shift occurred for precise philosophical reasons, most importantly Plantinga's free will defense which demonstrated the incoherence of claiming logical contradiction. This is not a "retreat" but rather development in philosophical precision.

"The evidential problem is strong enough to refute belief." This claim exceeds what the evidential problem can establish. Even the strongest formulations of the evidential problem claim only that evil makes God's existence "improbable," not "impossible." The difference is important in philosophical evaluation.

Why these responses are inadequate

They share a failure to understand the different logical natures of the two problems. The logical problem claims absolute logical impossibility, while the evidential claims relative improbability. This difference changes everything about how we approach them.

The Logical Problem of Evil (J. L. Mackie)

Mackie clearly formulated the logical problem in "The Miracle of Theism" (1982): the existence of an all-powerful and all-good God logically contradicts the existence of any evil in the world. The argument:

1. An all-good God wants to prevent all evil
2. An all-powerful God can prevent all evil
3. If God is all-good and all-powerful, then no evil will exist
4. Evil exists
5. Therefore, no all-good and all-powerful God exists

This argument claims absolute logical contradiction — like the contradiction between "square" and "circular." If correct, the existence of any evil, however small, would prove God's non-existence.

The Free Will Defense (Alvin Plantinga)

Plantinga's response in "The Nature of Necessity" (1974) and "God, Freedom, and Evil" (1977) was decisive. He did not attempt to prove that free will actually explains evil, but only that it is logically possible:

It is logically possible that creating free creatures capable of moral good is better than not creating them. It is logically possible that genuine freedom requires the possibility of doing evil. It is logically possible that God cannot create a world containing free creatures who always choose good (since this would contradict the meaning of freedom).

If these possibilities are correct, then there is no logical contradiction between God's existence and evil's existence. Importantly: Plantinga does not need to prove this explanation is correct, only that it is logically possible. This suffices to refute the claim of logical contradiction.

Philosophical consensus on Plantinga's success

Even atheist philosophers like William Rowe and Paul Draper acknowledged that Plantinga succeeded in refuting the logical problem. This is rare consensus in philosophy. The reason: claims of logical contradiction are very strong, and showing just one logical possibility suffices to refute them.

The Evidential Problem of Evil (William Rowe)

After Plantinga's success, discussion shifted to a weaker but more convincing formulation. Rowe in "The Problem of Evil and Some Varieties of Atheism" (1979) formulated the evidential problem:

1. There exist evils that appear to have no adequate moral justification
2. If God existed, there would be no unjustified evils
3. Therefore, it is very probable that God does not exist

The crucial difference: this argument does not claim logical impossibility, but improbability. Rowe acknowledges the possibility of unknown justifications, but considers this unlikely.

Rowe's famous example: a deer burning slowly in a natural forest fire and dying in severe pain. What possible moral justification could there be for this suffering? It does not appear to serve any greater good.

Why the evidential problem is more difficult

The logical problem only needs to show logical possibility. The evidential problem needs to evaluate probabilities — and this is much more difficult. It is not enough to say "perhaps there is a justification we don't know," but rather one must show this is sufficiently probable.

Responses to the evidential problem

1. The epistemological defense (Stephen Wykstra): Our cognitive limitations make us unable to judge the probability of justifications existing. Like an ant that cannot understand the reasons for human behavior.

2. Various theodicies: Attempts to provide probable justifications for evils (soul-building, free will, natural order, etc.).

3. Probabilistic criticism (Peter van Inwagen): The difficulty of determining precise probabilities in major metaphysical matters.

Where we stand in this debate today

Discussion has shifted from the logical problem (solved by consensus) to the evidential problem (still debated). This is development in philosophical precision, not retreat by any side. The evidential problem is logically weaker but emotionally stronger — it deals with the intuitive feeling that the quantity and quality of evil in the world is difficult to reconcile with a loving God.

The balanced position today acknowledges that the problem of evil remains the strongest challenge to theistic belief, but is not a decisive proof. It enters into the balance of evidence in the "rational probability" (rajḥān ʿaqlī) approach.

For advanced reading

─ Advanced level: the problem of divine hiddenness as an extension of the evidential problem
─ J. L. Mackie, "Evil and Omnipotence" (1955)
─ Alvin Plantinga, God, Freedom, and Evil (1977)
─ William Rowe, "The Problem of Evil and Some Varieties of Atheism" (1979)
─ Peter van Inwagen, The Problem of Evil (2006)
─ "Evil: Logical vs Evidential" page on the website