The Argument from Motion as Proof of God

Thomas Aquinas’s Five Ways stand as some of the most profound and enduring arguments for the existence of God in the history of philosophy and theology. Found in the Summa Theologica (I, Q. 2, Art. 3), these arguments rely on empirical observations and rigorous metaphysical reasoning. The First Way, often called the Argument from Motion, is not merely a defense of God’s existence but a masterclass in applying Aristotelian principles to theological inquiry. This argument’s precision and depth have influenced centuries of Christian philosophy, bridging faith and reason.

The First Way Explained: Motion and the Unmoved Mover

Aquinas begins with an undeniable fact: motion exists in the world. However, his definition of motion is broader than modern physics might suggest. For Aquinas, motion refers to the actualization of potentiality. Consider a block of marble: it is potentially a statue, but it requires a sculptor to actualize that potential. This principle, rooted in Aristotle’s metaphysics, frames the core of the First Way.

Aquinas’s argument can be summarized syllogistically:

1. Everything in motion is put into motion by something else.

2. If a thing is in motion, it cannot move itself, as it must be moved from potentiality to actuality by something already actual.

3. This chain of movers cannot go on infinitely, because without a first mover, there would be no motion now.

4. Therefore, there must exist a first, unmoved mover—pure actuality—that initiates motion in all things.

5. This unmoved mover is what we call God.¹

Philosophical and Theological Foundations

Aquinas observes that anything in motion must be moved by something else, as nothing can move itself. However, this sequence of movers cannot extend infinitely into the past, for such a chain would leave the current motion unexplained. Thus, there must exist a First Mover—itself unmoved—that initiates all motion. This being, Aquinas concludes, is God.² He writes:

“It is impossible that in the same respect and in the same way a thing should be both mover and moved… Therefore, whatever is in motion must be put in motion by another.”³

The Unmoved Mover must be pure actuality—entirely without potentiality—since potentiality implies the possibility of change.⁴ By necessity, this being is eternal, immaterial, and unchanging.⁵

Norman Geisler, an evangelical philosopher and theologian, praises the metaphysical depth of Aquinas’s argument:

“Aquinas’s First Way remains one of the most profound demonstrations of God’s necessity, showing that all change and motion ultimately depend on a First Mover.”⁶

William Lane Craig, another influential evangelical apologist, highlights how Aquinas’s argument complements modern cosmological arguments:

“The existence of motion requires an ultimate explanation that is itself outside motion. That explanation is God, who is not moved but moves all else.”⁷

J.P. Moreland adds:

“Aquinas shows that the ultimate cause of motion must be immaterial and unchanging, providing a metaphysical foundation for theism.”⁸

An Argument for God’s Existence

The First Way is more than a logical proof; it is a deeply theological statement. Aquinas does not merely posit a First Mover but identifies this mover with God. The attributes of the Unmoved Mover—eternal, immutable, immaterial—align with the God of classical theism. As Edward Feser explains, “The God of the First Way is not just a generic cause; He is the very act of existence itself, the ground of all being.”⁹

This argument also complements biblical theology. In Acts 17:28, Paul declares, “In Him we live and move and have our being.” Aquinas’s argument gives philosophical depth to this scriptural claim, showing that all motion and change ultimately depend on God, who is the unchanging ground of all reality.

Timothy Keller, an evangelical pastor and apologist, affirms the First Way’s power in apologetics:

“The necessity of a first cause of motion not only points to God’s existence but underscores His nature as the sustaining foundation of all creation.”¹⁰

Responding to Objections

While powerful, the First Way has faced challenges. David Hume argued that motion might be an inherent property of matter, needing no external cause.¹¹ However, Aquinas’s argument is not about physical motion alone but the broader metaphysical reality of change and causation. Hume’s critique misunderstands Aquinas’s premise, focusing on empirical causation rather than the deeper necessity of a First Cause.

Similarly, Immanuel Kant contended that arguments like the First Way illegitimately move from finite observations to infinite conclusions.¹² Yet, Aquinas does not simply infer God from the cosmos; he demonstrates the necessity of a being whose essence is existence itself, a principle Kant does not fully address.

Modern physics, particularly quantum mechanics, has been cited as a challenge, with claims that particles can appear without cause. However, these claims operate within an already-existing framework of laws and conditions. As William Lane Craig explains:

“Quantum events do not disprove causality; they presuppose it. Aquinas’s First Way addresses not individual events but the ultimate ground of all change.”¹³

Additionally, Aquinas’s metaphysical argument transcends physical causation. Alvin Plantinga clarifies this point:

“The First Way is not about scientific explanations; it is about the foundation of all reality. Even quantum mechanics cannot escape the need for an ultimate cause.”¹⁴

Contemporary Relevance

Aquinas’s First Way remains profoundly relevant in modern debates about the existence of God. While science explains the how of motion, Aquinas addresses the why. As Peter Kreeft aptly puts it, “The First Way shows that science itself presupposes metaphysics. Science asks about what moves, but philosophy must ask why there is motion at all.”¹⁵

Additionally, the First Way provides a robust framework for engaging with contemporary atheism. By demonstrating that the natural world cannot explain itself, Aquinas directs the conversation toward the necessity of a transcendent cause. Norman Geisler emphasizes:

“For evangelicals, Aquinas offers a timeless defense of theism that aligns with the biblical view of God as Creator and Sustainer.”¹⁶

Conclusion: Motion and the Divine

The First Way is both a philosophical and theological masterpiece. By beginning with the observable fact of motion, Aquinas leads us to the profound truth of God’s existence. The Unmoved Mover is not merely a theoretical construct but the foundation of all being and the source of all change. As Aquinas himself wrote, “There must be a first mover, itself unmoved, and this everyone understands to be God.”¹⁷

Aquinas’s argument invites us to see the world with fresh eyes, recognizing that every motion, every change, and every cause points to the eternal, unchanging God who sustains all things. In this way, the First Way is not just a proof of God’s existence but an invitation to worship the Creator who moves all things without Himself being moved.

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Click for Aquinas’ Second Way, Third Way, Fourth Way, Fifth Way

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¹ Thomas Aquinas, Summa Theologica, I, Q. 2, Art. 3.

² Ibid.

³ Ibid.

⁴ Edward Feser, Aquinas: A Beginner’s Guide (London: Oneworld, 2009).

⁵ Ibid.

⁶ Norman Geisler, Thomas Aquinas: An Evangelical Appraisal (Grand Rapids: Baker, 1991).

⁷ William Lane Craig, Reasonable Faith (Wheaton: Crossway, 2008).

⁸ J.P. Moreland, Scaling the Secular City (Grand Rapids: Baker, 1987).

⁹ Feser, Aquinas: A Beginner’s Guide.

¹⁰ Timothy Keller, The Reason for God (New York: Dutton, 2008).

¹¹ David Hume, Dialogues Concerning Natural Religion.

¹² Immanuel Kant, Critique of Pure Reason.

¹³ Craig, Reasonable Faith.

¹⁴ Alvin Plantinga, God and Other Minds (Ithaca: Cornell University Press, 1967).

¹⁵ Peter Kreeft, Summa of the Summa (San Francisco: Ignatius Press, 1990).

¹⁶ Geisler, Thomas Aquinas: An Evangelical Appraisal.

¹⁷ Aquinas, Summa Theologica, I, Q. 2, Art. 3.