Full Idea
Self-movement must move in some particular direction, but if it pushes it will be behind itself, and if it pulls it will be in front of itself.
Gist of Idea
Does the original self-mover push itself from behind, or pull itself from in front?
Source
Sextus Empiricus (Outlines of Pyrrhonism [c.180], III.68)
Book Reference
Sextus Empiricus: 'Outlines of Pyrrhonism', ed/tr. Bury,R.G. [Prometheus 1990], p.212
A Reaction
This is the same as Aquinas's First Way of proving God's existence.