The problem of evil is not the only objection to theism in contemporary philosophy, but it
has been by far the most prominent. Discussion of this problem
end p.431
has passed through at least two distinct phases. In the earlier period, represented by J. L.
Mackie's “Evil and Omnipotence” (1955) the claim commonly made was that the
existence of evil is logically inconsistent with the existence of God; this, then, is the
“logical problem of evil.” According to Mackie, the propositions that generate the logical
inconsistency are:
- God is omnipotent.
- God is wholly good.
- Evil exists.
According to Mackie, this contradiction shows, “not [merely] that religious beliefs lack
rational support, but that they are positively irrational, that the several parts of the
essential theological doctrine are inconsistent with one another” (200).
The classic response to Mackie's argument came in Alvin Plantinga's (1974) “free will
defense.” Plantinga's strategy is to prove that propositions (1) through (3) are consistent
with each other, by providing a fourth proposition that is consistent with (1) and (2) and
which, when conjoined with them, has (3) as a logical consequence. (Plantinga is relying
on a theorem of modal logic: {◊(p & q) & [(p & q) → r]} → ◊(p & r).) The proposition
Plantinga comes up with is in effect the following:^3 - God actualizes a world containing moral good, and it was not in God's power to
actualize a world containing moral good but no moral evil.
And from this, together with (1) and (2), it does indeed follow that - Evil exists.
The crucial claim here is that it is possible that it was not in God's power to actualize a
world containing moral good but no moral evil. The idea behind this is that moral good
(which is taken to be an especially valuable and important form of good) is possible only
for creatures possessing libertarian free will, but if God creates such creatures it is the
creature, and not God, who determines whether it does evil or good. So it may be that
whatever creatures of this sort God might have chosen to create, at least some moral evil
would result. An omnipotent God can control whatever he chooses to control, but even he
cannot both control and refrain from controlling at the same time.
As one might expect, Plantinga's argument resulted in prolonged and intensive
discussion. The upshot of this discussion is that it is now widely conceded, by atheists as
well as theists, that Plantinga's answer is successful, and that the existence of evil is not,
as such, logically inconsistent with theism. It is important, however, to recognize the
limitations of Plantinga's success. He has by no means
end p.432
shown by this argument (nor did he claim to show) that the evil in the world cannot
support an objection to belief in God. Nor does he claim by his argument to have
explained the existence of the evil that we see in the world. His argument is a defense,
which shows that a particular version of the problem of evil does not succeed; it is not a