Book 12
6
Yet if we accept the statements of the cosmologists who generate everything from Night,Cf. Hes. WD 17, Hes. Th. 116ff. or the doctrine of the physicists that all things were together,Cf. Aristot. Met. 12.2.3. we have the same impossibility; for how can there be motion if there is no actual cause? Wood will not move itself—carpentry must act upon it; nor will the menses or the earth move themselves—the seeds must act upon the earth, and the semen on the menses.
7
Hence some, e.g. LeucippusCf. Aristot. Met. 1.4.12, Aristot. De Caelo 300b 8, and see Burnet, E.G.P. 178. and Plato,Cf. Plat. Tim. 30a, and sect. 8 below. posit an eternal actuality, for they say that there is always motion; but why there is, and what it is, they do not say; nor, if it moves in this or that particular way, what the cause is. For nothing is moved at haphazard, but in every case there must be some reason present; as in point of fact things are moved in one way by nature, and in another by force or mind or some other agent. And further, what kind of motion is primary? For this is an extremely important point.
8
Again, Plato at least cannot even explain what it is that he sometimes thinks to be the source of motion, i.e., that which moves itself; for according to him the soul is posterior to motion and coeval with the sensible universe.Aristotle refers to Plato’s rather inconsistent account in Plat. Tim. 30-34. Now to suppose that potentiality is prior to actuality is in one sense right and in another wrong; we have explainedThe reference is probably to 5 above, but cf. Aristot. Met. 9.8. the distinction.
9
But that actuality is prior is testified by Anaxagoras (since mind is actuality), and by Empedocles with his theory of Love and Strife, and by those who hold that motion is eternal, e.g. Leucippus.
