Substance and what it means to be › An Eternal Source of Eternal Motion

Book XII.6–7 turns to an eternal unmoved substance. Aristotle's starting point here is eternal motion and time, including the everlasting circular motion he attributes to the heavens. He is seeking a principle adequate to that motion. The argument is not about a first event that happened before an otherwise motionless universe.

A merely potential source of motion would be insufficient, he argues, because a capacity need not be exercised. To account for motion that never fails, he requires a principle whose essence is actuality. In his argument, the unmoved mover is eternal and immaterial. These conclusions belong to a framework whose cosmological assumptions must themselves be assessed, rather than treated as observations established by the argument.

How could a source move something without itself undergoing change? XII.7 uses objects of thought and desire to introduce that possibility. An end can be the object toward which an activity is directed without being pushed or altered by that activity. Aristotle describes the first mover as moving in the manner of a final cause, as something loved.

Imagine a musician practicing in order to achieve an excellent performance. The intended performance helps explain why the practice is organized as it is, without acting like a hand physically pushing the musician. This analogy clarifies one kind of explanatory relationship. It does not prove that a celestial body desires an immaterial object, or supply the missing premises of Aristotle's cosmology. The difficult passage needs those limits to remain visible.

In XII.9 Aristotle characterizes divine thinking as thinking of thinking. His discussion seeks the best and most self-sufficient object for divine thought. It should not be casually expanded into a detailed account of providence or a creator's plans for human history. Nor does XII reduce neatly to one mover with no further complication: XII.8 relates additional unmoved substances to additional celestial motions. The primacy of one mover and the plurality discussed there both belong in an account of the text.