This essay examines the proofs for God’s existence advanced by Anselm of Canterbury and Thomas Aquinas. It outlines their principal lines of reasoning, evaluates their respective strengths and weaknesses, and considers the continuing philosophical value of each approach.
Anselm’s Ontological Argument
Anselm’s argument, presented in the Proslogion, defines God as “that than which nothing greater can be conceived.” From this definition Anselm infers that existence in reality must belong to God; otherwise a greater being could be imagined. The argument is therefore a priori, relying solely on the concept of God rather than empirical observation. Its central claim is that necessary existence is a perfection that cannot be withheld from the greatest conceivable being.
Aquinas’s Five Ways
Aquinas offers five a posteriori arguments in the Summa Theologiae. The first three Ways share a common structure: motion requires a first unmoved mover; causation requires a first uncaused cause; and contingent beings require a necessary being. The fourth Way appeals to degrees of perfection, positing a maximum standard of being. The fifth Way observes order and purpose in nature and concludes that an intelligent director orders all things toward their ends. Each proof begins from features of the observable world and reasons back to a first principle identified with God.
Strengths and Weaknesses
Anselm’s argument is formally elegant and highlights the logical implications of the divine concept. However, it has been criticised for treating existence as a predicate that adds to greatness, a point later developed by Kant. The argument also presupposes that the concept is coherent; if the notion of a greatest conceivable being is itself contradictory, the proof collapses.
Aquinas’s arguments possess empirical grounding and appeal to widely accepted principles of causality. Their cumulative effect can appear persuasive. Nevertheless, each Way faces objections. Modern physics questions the necessity of a first temporal cause, while the inference from design to a single intelligent agent remains contested. Aquinas’s reliance on Aristotelian metaphysics further limits the arguments’ appeal outside that framework.
The Value of These Arguments
Despite their limitations, both sets of arguments retain value. They illustrate different routes—conceptual and empirical—by which reason may approach the question of God. They also stimulate reflection on the limits of human knowledge and the assumptions underlying causal and modal reasoning. For undergraduates, engaging with these proofs develops skills in conceptual analysis and critical assessment of metaphysical claims.
Conclusion
Anselm and Aquinas present distinct strategies for demonstrating God’s existence. Anselm’s ontological proof rests on definition alone, whereas Aquinas’s Five Ways proceed from experience. Each approach encounters significant objections, yet both continue to encourage rigorous examination of the relationship between reason and religious belief.
References
- Anselm of Canterbury (1995) Proslogion. Translated by T. Williams. Indianapolis: Hackett Publishing.
- Aquinas, T. (1981) Summa Theologica. Translated by Fathers of the English Dominican Province. New York: Christian Classics.
- Davies, B. (2004) An Introduction to the Philosophy of Religion. 3rd edn. Oxford: Oxford University Press.
