The Argument from Contingency as Proof of God

Thomas Aquinas’s Five Ways form a timeless foundation for classical theism, presenting rational arguments for God’s existence. The Third Way, known as the Argument from Contingency, is one of his most philosophically profound and theologically rich proofs. Found in the Summa Theologica (I, Q. 2, Art. 3), it explores the distinction between contingent beings and a Necessary Being to answer one of the most fundamental questions of existence: Why is there something rather than nothing?

As Thomist philosopher Brian Davies notes:

“The Third Way does not merely ask whether the universe has a cause but why anything at all exists rather than nothing. It forces us to confront the ultimate dependency of existence.”¹

The Third Way Explained: Contingency and Necessity

Aquinas begins with the observable fact that many things in the universe are contingent—they exist but could have not existed. A tree grows, but it could have not existed if the seed had never been planted. Contingent beings require external causes for their existence, meaning there must have been a time when they did not exist.

If everything were contingent, there would have been a time when nothing existed. Yet, if nothing existed, nothing could come into being, because something cannot come from nothing. Aquinas writes:

“That which does not exist only begins to exist through something already existing.”²

This reasoning leads Aquinas to conclude that not everything can be contingent. There must exist a being whose existence is necessary—a Necessary Being—which owes its existence to no external cause and sustains all other contingent beings. Aquinas concludes:

“This all men speak of as God.”³

Philosophical Foundations: The Dependency of Contingent Beings

The Third Way rests on a key metaphysical principle: contingent beings cannot account for their own existence. A contingent being depends on external factors, but this chain of dependency cannot regress infinitely without a foundation. As Aquinas explains, infinite regress leaves the existence of contingent beings unexplained, requiring a Necessary Being to terminate the causal chain.

Philosopher Mortimer Adler expands on this:

“Aquinas forces us to recognize that the existence of contingent beings cries out for an ultimate explanation—a being whose existence is not contingent but necessary.”⁴

Modern philosopher Robert Koons elaborates:

“The argument from contingency is not merely about tracing back causes; it reveals the inherent instability of a reality composed solely of contingent entities. Without a necessary ground, contingency collapses into absurdity.”⁵

This Necessary Being does not depend on anything for its existence and must exist by the very nature of its essence. Aquinas’s Third Way demonstrates that contingent reality points inevitably to a metaphysical bedrock—a being that exists necessarily.

Theological Implications: God as the Necessary Being

Aquinas’s Necessary Being possesses attributes unique to the God of classical theism: self-existence, independence, and eternal unchangeability. These qualities align with the biblical description of God, particularly in Exodus 3:14, where God declares, “I AM WHO I AM,” emphasizing His self-existence and aseity.

Paul’s words in Acts 17:28 further affirm this truth: “In Him we live and move and have our being.” Aquinas’s Third Way provides the philosophical foundation for these biblical claims, showing that all existence is radically dependent on God.

As theologian John Frame notes:

“Aquinas’s Third Way articulates the biblical concept of God as not merely the Creator but the Sustainer of all existence, the one on whom all reality depends.”⁶

Responding to Objections

1. The Universe as Necessary:

Some critics argue that the universe itself might be necessary, negating the need for a Necessary Being. However, as philosopher Alexander Pruss explains:

“The universe is composed entirely of contingent parts. A collection of contingent entities cannot produce necessity; it merely aggregates contingency.”⁷

Even if the universe has always existed, it remains contingent, requiring an external explanation for why it exists at all.

2. Brute Fact Materialism:

Another objection is the idea that existence is a “brute fact” requiring no explanation. Edward Feser critiques this position:

“Brute fact materialism abandons the principle of sufficient reason, the foundation of rational inquiry itself. The Third Way restores the intelligibility of existence by pointing to a necessary ground.”⁸

As David Bentley Hart eloquently puts it:

“To dismiss existence as a brute fact is to abdicate reason entirely. The Third Way forces us to confront the ultimate dependency of reality.”⁹

3. Quantum Mechanics:

Some point to quantum mechanics, where particles seemingly arise from “nothing.” However, as philosopher William Lane Craig clarifies:

“Quantum events occur within an already existing framework of physical laws and space-time. The Third Way addresses why such a framework exists at all.”¹⁰

Quantum mechanics presupposes the existence of contingent reality, which must ultimately rest on a necessary being.

Contemporary Relevance

The Third Way remains a powerful argument for God’s existence in the modern age. While science explains mechanisms and processes, it cannot address why the universe exists at all. As Timothy Keller writes:

“Science explains how things work, but it cannot answer the ultimate question of why there is something rather than nothing. Aquinas’s Third Way fills that gap, pointing to God as the necessary explanation.”¹¹

Moreover, the Third Way challenges naturalism, which often assumes the self-sufficiency of the cosmos. As philosopher Richard Swinburne notes:

“The very existence of the universe cries out for explanation, and Aquinas’s argument from contingency provides a compelling answer.”¹²

Contingency and the Divine

Aquinas’s Third Way remains a masterpiece of philosophical and theological reasoning. By demonstrating that contingent beings cannot account for their own existence, Aquinas leads us to the necessity of a being whose essence is existence itself—a being we call God. As Aquinas concludes, “This all men speak of as God.”¹³

The Third Way not only answers the question, Why is there something rather than nothing? but also reveals the radical dependency of all creation on a God who is self-existent, eternal, and necessary. This argument invites us to see existence as a gift sustained by the God who is the ground of all being, making it as relevant today as it was in Aquinas’s time.

¹ Brian Davies, Thomas Aquinas’s Summa Theologiae: A Guide and Commentary (Oxford: Oxford University Press, 2014).

² Thomas Aquinas, Summa Theologica, I, Q. 2, Art. 3.

³ Ibid.

⁴ Mortimer Adler, How to Think About God (New York: Macmillan, 1980).

⁵ Robert C. Koons, The Kalam Cosmological Argument for God (London: Bloomsbury Academic, 2017).

⁶ John Frame, The Doctrine of God (Phillipsburg: P&R Publishing, 2002).

⁷ Alexander R. Pruss, The Principle of Sufficient Reason (Cambridge: Cambridge University Press, 2006).

⁸ Edward Feser, Aquinas: A Beginner’s Guide (London: Oneworld, 2009).

⁹ David Bentley Hart, The Experience of God: Being, Consciousness, Bliss (New Haven: Yale University Press, 2013).

¹⁰ William Lane Craig, Reasonable Faith (Wheaton: Crossway, 2008).

¹¹ Timothy Keller, The Reason for God (New York: Dutton, 2008).

¹² Richard Swinburne, The Existence of God (Oxford: Clarendon Press, 2004).

¹³ Aquinas, Summa Theologica, I, Q. 2, Art. 3.