Alvin Plantinga's free will defense

Alvin Plantinga's free will defense is a logical argument developed by American analytic philosopher Alvin Plantinga, the John A. O'Brien Professor of Philosophy Emeritus at the University of Notre Dame, and published in its final version in his 1977 book God, Freedom, and Evil. Plantinga's argument is a defense against the logical problem of evil as formulated by philosopher J. L. Mackie beginning in 1955. Mackie's formulation of the logical problem of evil argued that three attributes of God, omniscience, omnipotence, and omnibenevolence, in orthodox Christian theism are logically incompatible with the existence of evil. In 1982, Mackie conceded that Plantinga's defense successfully refuted his argument in The Miracle of Theism, though he did not claim that the problem of evil had been put to rest.

The logical argument from evil argued by J. L. Mackie, and to which the free will defense responds, is an argument against the existence of the Christian God based on the idea that a logical contradiction exists between four theological tenets in orthodox Christian theology. Specifically, the argument from evil asserts that the following set of propositions are, by themselves, logically inconsistent or contradictory:

Most orthodox Christian theologians agree with the first three propositions describing God as all-knowing (1), all-powerful (2), and morally perfect (3), and agree with the proposition that there is evil in the world, as described in proposition (4). The logical argument from evil asserts that a God with the attributes (1-3), must know about all evil, would be capable of preventing it, and as morally perfect would be motivated to do so. The argument from evil concludes that the existence of the orthodox Christian God is, therefore, incompatible with the existence of evil and can be logically ruled out.

Plantinga's free will defense begins by asserting that Mackie's argument failed to establish an explicit logical contradiction between God and the existence of evil. In other words Plantinga shows that (1-4) are not on their own contradictory, and that any contradiction must originate from an atheologian's implicit unstated assumptions, assumptions representing premises not stated in the argument itself. With an explicit contradiction ruled out, an atheologian must add premises to the argument for it to succeed. Nonetheless, if Plantinga had offered no further argument then an atheologian's intuitive impressions that a contradiction must exist would have remain unanswered. Plantinga sought to resolve this by offering two further points.

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