Per Se vs. Per Accidens Causal Series

Hello! Welcome back to our study of Aristotle's theory of the immovable mover.

Introduction

In our last lesson, we analyzed the foundational principle that 'whatever is moved is moved by another' (omne quod movetur ab alio movetur). We established that this is a direct metaphysical consequence of the distinction between potentiality and actuality. A thing cannot actualize its own potential, as it cannot give itself a quality it does not yet possess. We also saw how this principle withstands the challenge posed by Newtonian inertia, by distinguishing between motion as a state (inertial motion) and motion as a process of actualization (acceleration, alteration, etc.).

This principle naturally leads us to consider chains of movers: if A is moved by B, and B is moved by C, what does this chain of causation look like? Can it go on forever? Aristotle's answer, which is central to his argument for a first mover, depends critically on the type of causal chain we are examining.

Today's lesson directly addresses this crucial distinction. Our learning outcome is to explain the distinction between per se (essential, hierarchical) and per accidens (incidental) causal series. Understanding this difference is the final step we need before we can reconstruct Aristotle's argument against an infinite regress of movers.

1. Grounding the Terminology: Intrinsic vs. Coincidental Causes

Before we discuss causal series, let's first understand what Aristotle means by the terms per se (in itself, or intrinsically) and per accidens (coincidentally, or incidentally) as they apply to individual causes. This will provide a foundation for the more complex application to causal chains.

The Stanford Encyclopedia of Philosophy provides a clear explanation.

As the text explains, the distinction here is about explanatory relevance.

• An intrinsic (per se) cause is the cause described in a way that explains how the effect came about. "The sculptor" is the per se efficient cause of the statue because the art of sculpting is what produces the statue.
• A coincidental (per accidens) cause is a description of the cause that is true, but irrelevant to its causal role in producing the effect. If the sculptor is named Polyclitus, then "Polyclitus" is a per se cause. But if Polyclitus also happens to be a musician, "the musician" is only an accidental cause of the statue. It is accidental that the sculptor is also a musician.

This initial distinction helps us see that Aristotle is interested in the essential features of a causal relationship. We will now see how this same terminology is applied, in a more technical and crucial way, to entire chains of causes.

2. Two Fundamentally Different Causal Series

The core of today's lesson is distinguishing between two types of causal chains. The terms per se and per accidens are used again, but now they describe the fundamental structure of the series itself, not just the description of a single cause.

The following text by Dr. Michael Augros offers a clear and comprehensive explanation of these two types of series, complete with examples, defining properties, and formal definitions.

Let's break down and systematize the concepts from the reading.

The Per Accidens (Incidental) Series

This is a linear chain of causes and effects stretching back in time. Augros's example is a genealogy: a grandfather begets a father, who begets a son.

Key Properties:

• Sequential/Temporal: The causes typically act at different times. The grandfather's act of begetting is long past by the time the father begets the son.
• Independent Causal Power: Once a cause produces its effect, the effect possesses its own causal power. The father's ability to have a child is his own; it is not continuously derived from the grandfather. The grandfather could die, and this would not affect the father's ability to procreate.
• "Passing the Baton": The causal power is transferred from one member to the next. The prior cause is a sine qua non (without which, not), but not a concurrent, sustaining cause of the later cause's causation.
• Homogeneous Members: The members of the series are often of the same kind (e.g., a human begets a human).

Aristotle and Aquinas concede that such a series could, in principle, be infinite. Philosophy alone, they argue, cannot prove the universe had a beginning in time. An infinite series of past events (fathers begetting sons) is not considered logically impossible.

The Per Se (Essential / Hierarchical) Series

This is a hierarchical stack of causes, all operating simultaneously to produce a single effect. Augros's examples are excellent: the hand moves the stick, which moves the stone; or a sculptor moves a hammer, which moves a chisel, which carves the marble.

Key Properties:

• Simultaneous/Hierarchical: All causes in the series must act at the same time for the effect to occur. The stick only moves the stone while the hand is moving the stick. If the hand stops, the entire causal chain ceases to exist.
• Derived Causal Power: The causal power of every intermediate member is entirely derived from and dependent on the prior member. The stick has no power to move the stone on its own; it acts purely as an instrument of the hand.
• Instrumental Causation: The intermediate causes are instruments of the primary cause in the series. Their causality is borrowed.
• Heterogeneous Members: The members must differ in their nature and causal power (hand, stick, stone; or general, colonel, captain).

This is the type of series that Aristotle argues cannot be infinite. The entire chain of instrumental causes depends on a first member that is not itself an instrument—a primary mover.

3. A Computational Analogy

Given your background, a parallel from computer science might clarify the structural difference.

• A per accidens series is like a sequence of shell commands in a script that generates and then executes other scripts.

  • script_A.sh runs, performs its task, and as its last action, writes and executes script_B.sh.
  • script_A.sh can terminate. script_B.sh now runs independently, using its own allocated resources. It then writes and executes script_C.sh.
  • The existence of script_B was caused by script_A, but script_B's execution and its power to create script_C are its own. The causal link is historical.

• A per se series is like a nested function call stack.

  • main() calls function_A().
  • Inside function_A(), it calls function_B().
  • Inside function_B(), it calls function_C(), which finally performs an operation (the effect).
  • The operation in function_C can only happen because function_C is active. function_C is only active because function_B called it and is still running. function_B is only active because function_A called it, and main() is still executing. The causal power flows down the stack simultaneously from main(). If main() or function_A() were to terminate, the entire stack would collapse, and the final effect would not occur. The lower functions are instrumental to the higher ones.

4. Why This Distinction is Crucial

The entire force of Aristotle's argument for a first mover rests on this distinction. He is not arguing against an infinite past (an infinite per accidens series). He is arguing that any motion or change occurring right now must be sustained by a per se causal series that cannot be infinite.

Let's briefly touch on the intuition for why a per se series must have a first member.

The argument, in essence, is this: In a per se series, every intermediate cause is like a train car—it can pull the car behind it, but only because it is being pulled by the car in front of it. It has no engine of its own. An infinite series of train cars, with no engine, would result in no motion at all. The causal power is purely instrumental and must originate from something that has the power in a non-instrumental, non-derived way. An infinite chain of pure instruments is a chain with no actual power, and thus it cannot produce an effect.

Conclusion

Today we have made a critical distinction that underpins Aristotle's entire argument for a first mover. It is subtle but essential.

Key Takeaways:

• Causal series per accidens (incidental): A linear, temporal sequence where each member has its own causal power once created. The causal link is historical. Aristotle does not rule out the possibility of this type of series being infinite. (e.g., A father begets a son).
• Causal series per se (essential/hierarchical): A simultaneous, hierarchical stack of causes where intermediate members are mere instruments, deriving their causal power from a higher member. (e.g., A hand moves a stick, which moves a stone).
• The distinction is about the structure of dependency: in a per se series, the dependency is simultaneous and vertical; in a per accidens series, it is sequential and horizontal.
• Aristotle's argument against an infinite regress of movers applies only to per se causal series.

Preview of the Next Lesson:

With this distinction firmly in hand, we are now ready to tackle the argument head-on. In our next lesson, we will reconstruct Aristotle's formal argument for why a per se series of concurrent movers cannot be infinite, and therefore must terminate in a first member that moves the others.