97. Aristotle's Arguments for the Unmoved Mover

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Lecture Notes

Main Topics #

• The Composition of Self-Moving Things: Any thing that moves itself must have two distinct parts—one that moves (in act) and one that is moved (in potency). The moving part cannot itself be moved by the moved part, therefore one part must remain immobile.
• Per Se vs. Per Accidens Motion: If every mover is moved only per accidens (by accident), motion would not be necessary and could cease. But since motion is eternal, every mover cannot be moved per accidens. If moved per se (essentially), contradictions follow (e.g., simultaneous teaching and being taught the same science).
• Corruptible Self-Movers Cannot Explain Eternal Motion: Individual animals have beginnings and endings in time. If motion is eternal, the generation of corruptible things must be perpetual. But no individual corruptible thing, nor any collection of them existing at different times, can be the cause of this perpetuity.
• The Requirement for an Eternal Mover: Because corruptible self-movers cannot account for eternal motion, there must exist something perpetual and eternal that causes the perpetuity of generation in inferior things. This eternal mover itself must be moved by something unmoved either per se or per accidens.
• The Desirable as Unmoved Mover: Everything that moves itself is moved by appetite or desire. The mover (as part of the self-moving thing) moves because of desire for something desirable. The desirable itself is a mover that is wholly unmoved—this is the first separate mover (God).
• The Eternity of Motion Assumption: Aristotle assumes motion is eternal. Thomas notes this is not a weakness but the more difficult case: if God’s existence can be demonstrated even granting the world always was, it demonstrates God’s existence more strongly than if one only proved it for cases where the world had a beginning.

Key Arguments #

The Perpetuity Problem #

• Individual corruptible things that move themselves (animals) have temporal limits
• If motion continues eternally, the generation of such creatures must be perpetual
• No single corruptible creature can be responsible for this perpetuity (it is not always existing)
• No collection of such creatures, even infinite in number, can be responsible if they do not all exist together
• Therefore, there must be something eternal and perpetual causing this generational perpetuity

The Per Se vs. Per Accidens Distinction Applied to Motion #

• If “every mover is moved” is true per accidens only, then it is not necessary—motion could cease
• But Aristotle holds motion is eternal, so this cannot be merely accidental
• If “every mover is moved” is true per se (essentially), it leads to contradictions: a thing would move and be moved by the same thing in the same respect simultaneously
• Therefore, not every mover can be moved

The Moving Part Must Remain Unmoved #

• If something moves itself, it consists of two parts: moving part and moved part
• The moving part cannot be moved by the moved part (circular causality)
• The whole cannot move the part, nor the part move the whole (contradictions)
• Therefore, one part must be immobile while moving the other part
• The soul moves the body; though the soul is moved per accidens (when in a moving body), it is not moved per se

The First Mover Cannot Be Moved Per Se or Per Accidens #

• Animals (self-movers among us) have their moving part moved per accidens
• Because animals are corruptible and must be reduced to something incorruptible to account for eternal motion
• The first moving being must be moved by a mover that is neither moved per se nor per accidens
• This eternal, unmoved mover is what must cause the perpetuity of generation

Important Definitions #

• Immobile Mover (Unmoved Mover): That which causes motion without itself being moved either per se or per accidens. It must exist eternally and cannot be a body.
• Self-Moving Thing (ens seipsum movens): Something that moves itself, necessarily composed of a mover part (in act) and a moved part (in potency), with the mover remaining unmoved per se.
• Per Se (Through Itself): Belonging necessarily to something by its very nature; essential to it.
• Per Accidens (By Accident/Incidentally): Happening to belong to something contingently; not necessary to its nature.
• Moved Mover (Medium Movens): A thing that is moved by something else while moving something else; always dependent on a prior mover for its power.
• Desirable (Desideratum): That which is desired for its own sake; moves appetite without itself being moved; functions as an unmoved mover.

Examples & Illustrations #

The Teacher and Student #

• A teacher cannot be taught the same science while teaching it (in the same respect and at the same time)
• The teacher must possess knowledge in act; the student must lack it (be in potency)
• This illustrates how the mover and moved cannot be the same in the same respect regarding the same motion

The Ignorance in the Classroom #

• Berquist notes how a mentor (like Dr. Nohavut) uses a student’s inability to answer as an occasion to repeat a principle: “nothing gives what it doesn’t have”
• If the student doesn’t have the answer, they cannot give it
• This illustrates the basic principle underlying causality

The Animal and Its Motion #

• A sleeping animal wakes suddenly due to an external cause (a sound) not produced by itself
• The animal is not responsible for this motion that wakes it
• Therefore, animals cannot always be in motion by themselves—they depend on external stimuli

The Sun and Generation #

• Plants and animals depend on the sun’s position and motion for continuous generation
• Without the sun, there would be no continuous generation of plants or animals
• This suggests Aristotle’s ancient solution: heavenly bodies (eternal, incorruptible) cause motion in inferior things
• Modern understanding confirms this has “some probability”—without the sun there would be no perpetual generation on earth

The Desire for Immortality in Mortal Things #

• Individual animals cannot live forever, but through reproduction their species continues
• This is the mortal striving to be like the immortal so far as possible
• Shakespeare illustrates this in the Sonnets: “From fairest creatures we desire increase, / That thereby beauty’s rose might never die”
• The same principle applies to teaching (perpetuating knowledge), music, art—immortalizing something beyond one’s own life

Questions Addressed #

How Can Corruptible Self-Movers Account for Eternal Motion? #

• Answer: They cannot. No single corruptible creature, nor any collection of them, can be the cause of perpetual generation because (1) individually they are not always existing, and (2) collectively they are not all existing together. Therefore, there must be something eternal and perpetual responsible for this.

Is the First Mover a Body? #

• Answer: No. Because motion in the strict sense involves a body and potency-to-act. The first mover, being eternal and perpetual (not composed of potency and act in the way bodies are), cannot be a body. This points toward the limit of natural philosophy and the beginning of metaphysics.

Why Does Thomas Call the Eternal World Supposition “Most Efficacious” (via efficacissima)? #

• Answer: It is the more difficult case. If one can demonstrate God’s existence even assuming the world always existed, one has demonstrated it more strongly. Any reason for God’s existence that holds for an eternal world also holds for a created world, plus all the reasons from creation itself. Therefore proving God even on the harder supposition makes the proof more efficacious.

Does Aristotle’s Assumption of Eternal Motion Weaken His Argument? #

• Answer: Not necessarily. Thomas suggests Aristotle may be taking the more difficult case deliberately, like Euclid in geometry—demonstrating the hardest case and leaving easier cases to the reader. The point is to show that even granting motion is eternal, there must still be an unmoved mover.