Encyclopedia of Philosophy: AQUINAS' NATURAL THEOLOGY

Aquinas' most famous contribution to the philosophy of religion is the Five Ways or proofs of the existence of God to which he refers early in his Summa Theologiae. Motion in the world, Aquinas argues, is only explicable if there is a first unmoved mover; the series of efficient causes in the world must lead to an uncaused cause; contingent and corruptible beings must depend on an independent and incorruptible necessary being; the varying degrees of reality and goodnesss in the world must be approximations to a subsistent maximum of reality and goodness; the regular teleology of non-conscious agents in the universe entails the existence of an intelligent universal Orderer. Several of the Five Ways seem to depend on antiquated physics, and none of them has yet been restated in a manner clear of fallacy. Recently, philosophical interest has turned to the long and complicated argument for God's existence presented in the Summa contra Gentiles; it will be interesting to see whether it can be restated in a way which will carry conviction to the unbeliever.