Some philosophers attributed the movements of celestial spheres to celestial souls with intention and will. They classified motion as natural, compelled, or voluntary, then argued that the heavenly motion required the third class.
The commentary objects that the classification must first be shown to exhaust the relevant possibilities; circular or sustained movement does not, by itself, prove a separate intending soul. Assumptions about the ancient spheres also enter the argument.
Voluntary celestial movement here names a feature of historical philosophy, not a verified account of contemporary astronomy.