According to the English philosopher and theologian John Hick, Christian theology offers two main approaches to theodicy, one stemming from the work of St. Augustine (Augustine, Saint) (354–430), the other from that of St. Irenaeus (Irenaeus, Saint) (c. 120/140–c. 200/203). Augustine's approach has been much more influential, but Hick finds the ideas of Irenaeus more in harmony with modern thought and likely to prove more fruitful.

The Irenaean view, by contrast, looks to the future and assumes an evolutionary perspective. Adam's sin is seen mainly as a lapse due to weakness and immaturity. The Fall is understood not as a catastrophe for the human race but as something from which humans can learn. In this account, the world is seen as a mixture of good and evil, an environment of growth and development in which humans can mature toward the perfection for which they were created by God.

There are numerous other philosophical approaches to theodicy. There is, for example, the view that evil is not an actually existent reality but rather the absence of some good, such as sight, health, love, or moral virtue. This view is found in the works of Augustine and St. Thomas Aquinas (Aquinas, Thomas, Saint), the 13th-century Dominican theologian, and in the Theodicy (1710), by the German philosopher and mathematician Gottfried Wilhelm Leibniz (Leibniz, Gottfried Wilhelm). According to Leibniz, there are three forms of evil in the world: moral, physical, and metaphysical. Using Augustine's analogy of a picture with dark patches (what strikes one as ugly in itself may nevertheless add beauty to the whole), Leibniz argues that it is best to have a world of rich variety and “plenitude.” In this view, God chose which world to create from an infinite number of possible worlds that were present as ideas in his mind. Since he wills what is best, the world he created has the greatest possible number of compatible perfections; in Leibniz's phrase, it is the “ best of all possible worlds.” This view was famously satirized in Candide (1758), by the French Enlightenment writer Voltaire.

Both the Augustinian and the Irenaean approaches appeal to free will: the occurrence of moral evil (and, for Augustine, natural evil) is the inevitable result of human freedom. These views are based on the assumption that, because free will is good, both in itself and because it enables individuals to take responsibility for their own actions, God permits sin (moral evil) as the price of freedom. Although Augustine stressed the “fallenness” of the natural world, both he and Irenaeus paid tribute to its beauty, intricacy, and suitability as an environment for human life. Drawing on this understanding, the English theologian Richard Swinburne has argued that the regularities of natural events (which can harm human beings as well as benefit them) are a necessary condition of both an individual's moral growth and his intellectual development. Thus although fires and floods are dangerous and destructive, they offer people opportunities to exercise virtues such as bravery and self-sacrifice and to take steps to make themselves safer in the future.

Although many people are helped to grow and to mature through suffering, many too are broken or destroyed by it. Hence, a further common strategy is to appeal to a life after death; the hardships of this life, whether caused by natural evil or by moral evil, are as nothing compared with the rewards to come, and they are a necessary factor in preparing one for the afterlife through moral training and maturation. This line of thought, however, must amount to more than saying that there will be rewards in heaven for suffering endured in the world. As the Russian novelist Fyodor Dostoyevsky (Dostoyevsky, Fyodor) argues in The Brothers Karamazov (1879–80), an appeal to a putative compensation in the afterlife and an “eternal harmony” must not be used to avoid the issues of justice and atonement. The English mystic Julian of Norwich (born 1342) resolved this problem by noting that part of the bliss and fulfilment of those who are saved will be that, at the Last Day, they will see the true reason why God has done all the things he has and the reason too for all the things he has permitted.

Although these strategies may at first seem plausible, the existence of horrendous evil in the world seems ultimately to undermine them, according to some critics. Little or nothing good came out of Auschwitz, for example, and nothing can compensate for it. Many thinkers, therefore, appeal to mystery at a certain point or cast their discussions as defenses rather than as theodicies.