The problem of natural evil is a specific form of the problem of evil, the problem of reconciling the existence of evil with the existence of God. If God is all-knowing, benevolent, and all-powerful, then why does he allow evil to occur?

There are two kinds of evil in the world: moral and natural; both appear to exist in abundance. Moral evils are those evils that are freely inflicted upon humankind by humankind: deceit, murder, theft, etc.; they result from the choices of free agents. Natural evils are those evils that occur as the result of natural processes: earthquakes, forest fires, tsunamis, etc. The problem of natural evil is thus the problem of explaining why God allows this latter kind of evil to occur.

The most common response to the problem of evil—the free will defence—holds that God rightly chose to create humankind free, and that evil is the result of our abuse of that freedom. Evil is not God’s fault; it is ours. This defence applies only to moral evil; natural evil does not result from the choices of free agents, and so cannot be justified in this way. Natural evil therefore poses a greater threat to belief in God than moral evil.

Two generic responses to the problem of evil question its fundamental assumptions. The first denies that God is morally good, casting doubt on whether he would prevent evil if he were able to; the second denies that evil exists, casting doubt on whether there is a problem to solve at all.

The Free-Will Defence and Natural Evils

There is, however, an alternative response to the problem of natural evil, associated with St Augustine, that grants that evil exists but denies that any of it is natural. If this position can be maintained, then it will be possible to extend the free-will defence to cover not only those evils usually categorised as moral evils, but also those usually categorised as natural.

The defence works by suggesting that so-called natural evils—earthquakes, epidemics, etc.—are the work of demonic forces, fallen angels. They are, it is suggested, no less the result of free will than evils normally classified as moral. This defence thus effectively denies the existence of natural evils, holding that all evils result from the choices of free agents, and so that all evils are moral.

Natural Evil is a Punishment for Sin

Another attempt to solve the problem of natural evil sees such evil as a just punishment for sin inflicted upon us by God. We cannot complain about natural evils, on this view, because we deserve all that we get. Natural evil, unpleasant though it may be, belongs in the world; it makes the world more just.

The chief difficulty with this view is that nature is a crude instrument of retribution; it often smites hardest those that have sinned least. The argument may succeed in casting some doubt on the supposition that a good God would eliminate all suffering; God’s benevolence and his justice may exist in tension, and a benevolent God may sometimes will just punishment. It does not, however, explain the unequal distribution of natural evil that we observe.

Good Cannot Exist Without Evil

Perhaps a more robust approach to resolving the problem of natural evil is that which holds that it is necessary for the universe to contain some evil in order for it to contain some good. Good and evil, according to this position, are relative terms, like up and down or past and future; one cannot have one unless one has both. If this is correct, if it is impossible for one to exist without the other, then perhaps God was justified in creating a world containing evil because it was only by doing so that he could create a world containing good.

Evil Makes Higher-Order Goods Possible

Even if the previous suggestion is resisted, a similar argument might be proposed, holding that evil is necessary in order for certain types of good to exist. Specifically, the existence of evil allows for goods that oppose evil, opening up possibilities for bravery, for compassion, and for mutual dependence, for example. These higher-order goods could not exist otherwise. A world without suffering would lack such goods as these, and would therefore be inferior.