Most people who’ve thought about whether God exists have also thought about how the presence of evil in the world bears on this question. Many have supposed that evil is incompatible with God’s existence, and since there’s obviously quite a lot of evil in the world, it follows that God doesn’t exist.
Of course, the main premise in that argument is the incompatibility thesis. Why think that it’s true? The classic argument is something like this: God is supposed to be omnipotent and morally perfect. If he’s omnipotent, he can do anything whatever. If he’s morally perfect, he will ensure the absence of evil as far as his power allows. Hence, if it were true that God exists, there’d be no evil.
There are many avenues available to the theist to respond to an argument of this kind. One obvious way is simply to argue that one of the premises is false. For example, one might argue that omnipotence, properly understood, doesn’t involve the power to do anything whatever, since it is incoherent to suppose that something do something that is impossible (e.g. draw a round square). Actions that involve contradictions are not within the scope of any possible being’s power, so the argument at best targets a conception of theism no theist should endorse.
Another avenue is to show that evil is compatible with God’s existence. The theist can do this by telling a coherent story in which God exists and there is evil. One particularly influential example of this is the so-called free will defence. Consider the following story.
God, being perfectly loving and wanting to share the joys of existence with others, creates people who he knows will never do evil. Moreover, God desires that these people be genuinely free with respect to their morally significant actions, i.e. actions they are morally obliged to perform or refrain from performing. Suppose, then, that God creates Eve knowing that she will in fact never go wrong. When the serpent tempts her to disobey God and do evil, she freely refuses, just as God expected.
That seems like a coherent story to me. No contradictions are apparent. Mightn’t a good being have very good reason to create saintly agents who he knows will never do evil?
If you answered in the affirmative, then you should agree that God’s existence is at least compatible with evil, provided that you also believe that free will requires that one have the ability to do otherwise. Thus, if you freely perform an action A, then you might’ve refrained from performing A on that occasion. That is, your performing A wasn’t predetermined.
The reason is simple: If Eve freely obeyed God on that occasion, then it’s possible that she disobeyed God on that occasion. That’s precisely what ‘can do otherwise’ involves, according to the above thesis. But it is possible that Eve disobeys God on that occasion only if it’s possible that God exists whilst something bad has happened. Put in terms of philosophy’s favourite conceptual tool of ‘possible worlds,’ if Eve actually freely obeys God and refrains from doing evil on some occasion, then there is a possible (but not actual) world in which she disobeys God by doing evil. But a person can disobey someone only if he exists; one cannot disobey a non-existent thing. Hence, in the possible world in which Eve does evil, God exists, and since it is a possible world, it follows that God’s existence is logically consistent with the existence of evil.
The moral is that God can create free creatures only by, as it were, risking that they will sometimes do evil. Since it seems possible that a perfectly loving being might want to create free creatures, any argument that involves the premise that God’s existence is logically incompatible with evil is suspect. Perhaps God doesn’t exist, but the logical argument from evil isn’t a good enough reason to suppose that he doesn’t exist. Atheists must appeal to other arguments.
This is a very brief summary of my and Nathan Helms’ essay ‘A Simpler Free Will Defence,’ published in the International Journal for Philosophy of Religion, which can be read here: https://link.springer.com/article/10.1007/s11153-015-9512-7
About the Author: C'Zar Bernstein is a philosopher who has published peer-reviewed work in journals such as Philosophia, International Journal for Philosophy of Religion, Public Affairs Quarterly, and the Journal of Medicine and Philosophy. His present interests include topics in applied and medical ethics. He earned his postgraduate degree in philosophy from Oxford and is presently a law student at The George Washington University Law School.