ABSTRACT
Having outlined the contours of Christian ontology, our task in the next two sections is to address the question of their rational justification and warrant. Christian theologians draw a distinction between natural and revealed theology. Natural theology seeks to derive knowledge of God from the natural order-of-things via inductive and deductive reasoning. Thomas Aquinas’ five ‘demonstrations’ of the existence of God take the form of inductive inferences drawn from observation of nature (Aquinas 1920, vol. 1, pp. 19ff.; Kenny 2008). The first three are variations on what became known as the ‘cosmological argument’: objects in the natural world are in a constant state of motion, and since motion cannot extend into infinity there must be an ‘unmoved mover’; nature consists of a network of efficient causes, and since there can be no infinite regress there must be a ‘first cause’; since the contingent world has the potentiality not to exist, its continuing existence must be due to a ‘necessary being’. The fourth ‘moral’ argument proceeded from the gradation of goodness in the universe to the necessity of an ‘infinitely good being’. The fifth ‘teleological’ or ‘design’ argument proceeded from the order and purpose inherent in the universe to an intelligent creator. Anselm’s ontological argument seeks to deduce God’s existence from the suggestion that an absolutely perfect being would be less than perfect if it did not actually exist (Anselm 1962, pp. 7ff.; Plantinga 1968). A renewed interest in these scholastic arguments at the start of the Enlightenment quickly gave way to widespread scepticism regarding their viability. Aquinas’ a posteriori arguments faced criticism from Humean empiricists, who rejected the Aristotelian understanding of causality on which they were dependent, as well as from Darwinian evolutionists. Anselm’s a priori argument faced the dual challenge of the anti-idealist rejection of deductive reasoning from first principles and the Kantian denial that ‘existence’ is a predicate. Despite the subsequent appearance of a series of robust defences of natural theology, the modern era saw a relative decline in its influence, particularly among Protestant theologians (Mackie 1982; Swinburne 1993, 2004). In the case of the latter, this was not primarily due to a perception that natural theology was struggling to sustain its intellectual credibility, but rather to the fact that the God whose existence natural theology sought to demonstrate was the God of classical theism rather than the God of the Trinitarian faith.
