What Is the Problem of Evil?

What Is the Problem?

The problem of evil is the most widely cited argument against the existence of God, specifically against the God of classical theism—a being who is all-powerful, all-knowing, and perfectly good. The argument starts from an undeniable fact: evil exists. There is suffering, cruelty, disease, natural disaster, betrayal, and death. The argument then presses the question: if God is all-powerful, God can prevent evil; if God is all-good, God wants to prevent evil; so why does evil exist? The tension is between the existence of evil and the existence of a God with the classical attributes.

The problem comes in two main versions, and they shouldn't be confused. The logical problem argues that the existence of evil is logically inconsistent with the existence of God—that the claims "God exists" and "evil exists" can't both be true. The evidential (or probabilistic) problem concedes that the two are logically compatible but argues that the amount and distribution of evil make God's existence improbable. The distinction matters because the two versions require different replies: the logical problem can be answered by showing a possible consistency, while the evidential problem requires showing that evil is probable on theism.

The Logical Version

The logical version was sharpened by J. L. Mackie in his 1955 essay "Evil and Omnipotence." Mackie's formulation runs: God is omnipotent; God is wholly good; evil exists. The three claims, Mackie argues, are jointly inconsistent, unless the theist can add a premise showing that God has a morally sufficient reason for permitting evil. The good in question would have to be such that it couldn't be achieved without permitting evil, or such that the evil is necessary for the greater good. Mackie argued that the standard theistic moves (free will, soul-making) don't provide such a premise, because a genuinely omnipotent God could achieve the goods without the evil.

The logical version is demanding, because it claims inconsistency, and inconsistency is a high bar. To show inconsistency, you need to show that there's no possible way the claims could all be true together. The theist only needs to show one possible way for them to be consistent to defeat the logical problem. Alvin Plantinga's free will defense, developed in the 1970s, is widely regarded as having met this burden: it describes a possible world in which God, free creatures, and evil coexist, with God having a morally sufficient reason (the value of free will). Most philosophers now agree that the logical version, as Mackie formulated it, fails, though the evidential version remains live.

The Evidential Version

The evidential version, developed by William Rowe in the 1970s and 1980s, concedes the logical consistency but presses on probability. Rowe's argument uses a case: a fawn caught in a forest fire, suffering for days before dying. The fawn's suffering seems to serve no greater good that an omnipotent God couldn't achieve without it. Rowe argues that, given cases like this, it's probable that there exist instances of intense suffering that serve no greater good, and that this is improbable on theism (since a good God would prevent pointless suffering) but expected on naturalism. So the existence of apparently pointless evil is evidence against God.

The evidential version is harder to answer than the logical one, because the theist can't just show possible consistency; she has to show that evil is probable on theism, or at least that the apparent pointlessness of some evil doesn't significantly lower the probability of God. The main replies are theodicies (which try to explain why God permits evil) and skeptical theism (which argues we're not in a position to judge what reasons God might have). The debate has become technically sophisticated, with Bayesian formulations of the probabilistic reasoning on both sides.

Moral and Natural Evil

The problem divides evil into two kinds. Moral evil is evil that results from the free choices of creatures: murder, betrayal, cruelty, war. Natural evil is evil that results from the natural order: disease, earthquake, famine, animal suffering. The distinction matters because the two kinds call for different theistic replies. Moral evil is typically handled by the free will defense: God values free creatures, and free creatures can choose evil; a world with free creatures and some evil is better than a world without free creatures. Natural evil is harder to handle this way, since it doesn't result from human choice—though some theists have argued that natural evil results from demonic free will, or that it's the condition for soul-making, or that it's a necessary feature of a stable natural order.

The SEP entry on the problem of evil treats the distinction as central to the structure of the debate. The free will defense addresses moral evil directly; natural evil requires additional resources, whether soul-making theodicies, the demonic-free-will hypothesis, or appeals to the necessity of natural law for a stable world. The difficulty of handling natural evil is one reason the evidential version, with its focus on natural evils like the fawn's suffering, has been so persistent.

The Main Theistic Replies

The free will defense, developed by Plantinga, argues that God values significantly free creatures—creatures who can choose between good and evil—and that a world with such creatures, even at the cost of some evil, is better than a world of programmed automata. The defense shows that God and evil are logically consistent, given the value of free will. Its scope is debated: it handles moral evil well, but its application to natural evil is contested.

The soul-making theodicy, developed by John Hick, argues that the world is designed not for maximal pleasure but for the development of moral and spiritual character—soul-making. A world without challenge, suffering, or difficulty would produce no courage, no compassion, no moral growth. Evil, on this view, is the necessary condition for the formation of virtuous souls. The theodicy has been criticized for suggesting that humans are means to God's ends, and for the scale of suffering it seems to require.

Skeptical theism, developed by Stephen Wykstra and others, argues that we're not in a position to judge whether God has a morally sufficient reason for permitting any particular instance of evil. God's knowledge is vastly greater than ours, and the goods connected to a given evil might be beyond our comprehension. The reply has been criticized for risking global skepticism (if we can't judge God's reasons, what can we judge?) and for undercutting theodicies that do try to explain evil. The SEP entry treats it as a serious but double-edged reply.

Why It Matters

The problem of evil matters because it's the most visceral of the arguments against God. The cosmological and teleological arguments are abstract; the problem of evil is concrete. It asks about real suffering—about a child's cancer, about a mother's grief, about a flood that drowns thousands. If theism can't make sense of this, theism is in trouble, however well the positive arguments go. And if naturalism can't ground the moral horror we feel at evil, naturalism is in trouble too. The problem is not just an argument against God; it's a test of any worldview's capacity to make sense of suffering.

The problem also matters because it forces theists to clarify what they mean by God's goodness and power. If God's goodness is such that God permits evil for the sake of greater goods, then God's goodness is more complex than a simple desire to prevent suffering. If God's power is such that God can't achieve the goods without the evil, then God's power is more constrained than omnipotence suggests. The problem of evil, in forcing these clarifications, sharpens the concept of God even for those who don't find the argument decisive. The SEP entry treats it as the most serious challenge to theism, and as one that has driven the development of theistic philosophy for centuries.

Sources

• Stanford Encyclopedia of Philosophy, "The Problem of Evil" — https://plato.stanford.edu/entries/evil/
• Stanford Encyclopedia of Philosophy, "Philosophy of Religion" — https://plato.stanford.edu/entries/philosophy-religion/
• Stanford Encyclopedia of Philosophy, "Augustine" — https://plato.stanford.edu/entries/augustine/
• Stanford Encyclopedia of Philosophy, "Hume" — https://plato.stanford.edu/entries/hume/

Related Topics

• Does God Exist? — the broader debate this argument belongs to.
• What Is a Theodicy? — the general project of replying.
• What Is the Free Will Defense? — the main reply to moral evil.
• What Is the Soul-Making Theodicy? — Hick's reply to natural evil.
• What Is Natural Evil? — the harder half of the problem.