In the philosophy of religion, the problem of evil is the question of how to reconcile the existence of evil with that of a deity who is, in either absolute or relative terms, omnipotent, omniscient, and omnibenevolent. An argument from evil attempts to show that the co-existence of evil and such a deity is unlikely or impossible if placed in absolute terms.
Logical problem of evil
The originator of the logical problem of evil has been cited as the Greek philosopher Epicurus, and this argument may be schematized as follows:
If an omnipotent, omniscient, and omnibenevolent god exists, then evil does not.
There is evil in the world.
Therefore, an omnipotent, omniscient, and omnibenevolent God does not exist.
This argument is of the form modus tollens, and is logically valid if its premises are true, the conclusion follows of necessity. To show that the first premise is plausible, subsequent versions tend to expand on it, such as this modern example:
God is omnipotent, omniscient, and omnibenevolent.
An omnibenevolent being would want to prevent all evils.
An omniscient being knows every way in which evils can come into existence, and knows every way in which those evils could be prevented.
An omnipotent being has the power to prevent that evil from coming into existence.
A being who knows every way in which an evil can come into existence, who is able to prevent that evil from coming into existence, and who wants to do so, would prevent the existence of that evil.
If there exists an omnipotent, omniscient, and omnibenevolent God, then no evil exists.
Evil exists (logical contradiction).
Both of these arguments are understood to be presenting two forms of the logical problem of evil. They attempt to show that the assumed propositions lead to a logical contradiction and therefore cannot all be correct. Most philosophical debate has focused on the propositions stating that God cannot exist with, or would want to prevent, all evils (premises 3 and 6), with defenders of theism (for example, Leibniz) arguing that God could very well exist with and allow evil in order to achieve a greater good.
One greater good that has been proposed is that of free will, famously argued for by Alvin Plantinga in his free will defense. The first part of this defense accounts for moral evil as the result of free human action. The second part of this defense argues for the logical possibility of “a mighty nonhuman spirit” such as Satan who is responsible for so-called “natural evils”, including earthquakes, tidal waves, and virulent diseases. Some philosophers agree that Plantinga successfully solves the logical problem of evil, by showing that God and evil are logically compatible though others explicitly dissent. The second part of Plantinga’s defense, though, concedes God’s omnipotence by claiming the possibility of “a mighty nonhuman spirit” capable of causing evil in spite of God’s desire for evil not to exist (a necessary consequence of His benevolence), effectively “overpowering” God.