What is the difference between the "First Cause" (temporal series) and the "First Mover" (metaphysical series) in Aquinas's thought?

The Distinction Between "First Cause" and "First Mover" in Thomas Aquinas

The distinction between the "First Cause" (Prima Causa) and the "First Mover" (Primum Movens) in Thomas Aquinas is among the most subtle issues in his philosophy, revealing the depth of his understanding of Aristotelian metaphysics and his development of it. This distinction is not merely a difference in terminology, but reflects a profound understanding of the nature of causality and being.

Inadequate Responses to Avoid

From some defenders of Aquinas:

"Both refer to God, so there's no essential difference." This is an unhelpful oversimplification. Aquinas distinguishes precisely between different patterns of causality, and each pattern reveals a different aspect of the relationship between God and the world. Conflating them deprives the arguments of their philosophical precision.

"The First Mover concerns physical motion, the First Cause concerns creation." Another oversimplification. "Motion" in Aquinas is not merely spatial displacement, but every transformation from potency to act, which is a profound metaphysical concept.

From some critics:

"Aquinas confuses temporal and logical series." This is an imprecise accusation. Aquinas is fully aware of the difference; indeed, his distinction between accidental (per accidens) and essential (per se) series is among his most important philosophical contributions.

"Both assume the impossibility of infinite regress, which is mistaken." This criticism requires careful examination. Aquinas does not reject every infinite regress, but distinguishes between different types of regress.

Why These Responses Are Inadequate

They fail to understand the precise structure of Aquinas's thought and his complex philosophical distinctions. The difference between the First Mover and the First Cause is not merely a difference in formulation, but reflects a deep understanding of the nature of being and causality.

The First Mover: The Metaphysical Series

In the First Way from the Summa Theologiae (I.2.3), Aquinas presents the argument of the First Mover. The basic concepts:

Motion in the Aristotelian sense: Not merely spatial displacement, but every transformation from potency (potentia) to act (actus). The growth of a tree, human learning, the transformation of water to steam—all are "motions."

The principle of motive causality: Everything that is moved (transformed from potency to act) requires an external mover in act. Nothing moves itself in the precise sense, because this would require being in potency and act at the same time and in the same respect, which is contradictory.

The essential series (per se): A series in which each member depends on the previous one for its current existence and current activity. Example: the hand moves the stick, and the stick moves the stone. If the hand stopped, the stick and stone would stop immediately.

The impossibility of regress in this series: In an essential series, infinite regress is impossible because all the intermediate members are merely transmitters of activity, not its source. Without a first mover in pure act, there would be no motion at all.

The First Cause: The Causal Series

In the Second Way, Aquinas presents the argument of the First Cause. Despite apparent similarity, there are essential differences:

Efficient causality: Concerns the production of being, not merely transformation. Parents are the efficient cause of their child, fire is the efficient cause of heat.

Causal ordering: In the world of experience, we find causal ordering: A causes B, and B causes C. Nothing causes itself (a thing preceding itself is impossible).

The essential causal series: Here too Aquinas distinguishes between accidental series (grandparents, parents, and children) and essential ones (simultaneous hierarchical causes). Only in the latter is regress impossible.

Essential Differences

Nature of the relationship:
- First Mover: continuous moving relationship (God moves the world now)
- First Cause: relationship of bringing into being and preserving in existence

Type of dependence:
- In motion: dependence in transformation from potency to act
- In causality: dependence in being itself

Temporality:
- First Mover: does not require a temporal beginning of the world (the world could be eternal and still need a mover)
- First Cause: likewise does not require a temporal beginning (essential causality is simultaneous)

Illustrative Example

Imagine a train of cars. In the First Mover model: the locomotive pulls the first car, which pulls the second, and so on. Each car moves by the locomotive's power transmitted through the series. If the locomotive stopped, the entire train would stop immediately.

In the First Cause model: a factory produces the cars. The cars exist because of the factory, but after production they remain in existence even if the factory is destroyed. But—here's the precision—Aquinas speaks of a deeper causality: causality of preserving existence, not merely initial production.

Theological Application

For Aquinas, God is both the First Mover and the First Cause, but in different senses:

As First Mover: God is pure act (actus purus) without potency. Every transformation in the world ultimately depends on His pure act. This explains the world's dynamism and continuous change.

As First Cause: God is subsistent being itself (ipsum esse subsistens). Every existing thing participates in His being. This explains the world's existence and continuance.

Contemporary Criticism and Defense

Anthony Kenny in "The Five Ways" (1969) criticized the distinction, claiming that Aquinas confuses types of causality. But Edward Feser in "Aquinas" (2009) and "Five Proofs" (2017) strongly defended the precision of Aquinas's distinction.

The basic problem in much contemporary criticism: reading Aquinas through modern Humean lenses, where causality is merely temporal succession. Aquinas works with a richer Aristotelian concept of causality.

Where We Stand in This Debate Today

The distinction between First Mover and First Cause remains philosophically important. Contemporary analytic philosophy has begun to revive interest in Aristotelian-Thomistic distinctions (Neo-Aristotelian revival). Philosophers like David Oderberg and Alexander Pruss are developing contemporary formulations of these ideas.

The basic lesson: philosophical precision matters. Confusing types of causality weakens philosophical arguments. Understanding Thomistic distinctions helps in appreciating the depth of the philosophical tradition and the possibility of benefiting from it in contemporary discussions.

For Advanced Reading

- Advanced level: The distinction between esse and essentia in Aquinas and its relation to causality
- Advanced level: Duns Scotus's critique of the Thomistic distinction
- Thomas Aquinas, Summa Theologiae I.2.3
- Edward Feser, Aquinas (Oneworld, 2009), Chapter Three
- Gaven Kerr, Aquinas's Way to God (Oxford UP, 2015)
- David Oderberg, Real Essentialism (Routledge, 2007)
- "Aquinas's Five Ways" page on the website