Full Idea
Aristotle undoubtedly considered the central characteristic of the ultimate cause of change to be activity [energeia].
Gist of Idea
The main characteristic of the source of change is activity [energeia]
Source
report of Aristotle (Metaphysics [c.324 BCE], Bk 12) by Vassilis Politis - Aristotle and the Metaphysics 8.8
Book Reference
Politis,Vasilis: 'Aristotle and the Metaphysics' [Routledge 2004], p.281
A Reaction
Aristotle identifies this, of course, with his 'God', but it strikes me that the word 'power' (as in Molnar) seems to capture Aristotle's concept. We just need some fundamental active force to get the whole shebang going.