The Hierarchical Causal Series of FIDO

FIDO is having existence imparted to it by C, B and A. None of the causes mentioned so far can act independently of some prior cause. This sort of causal series cannot regress infinitely. There would be no such series at all unless there were a cause which could impart existence without having to derive it itself. The first or primary cause in the present series then can only be something the very essence of which is identical to existence,. And that entails for St. Thomas that it must be caused by God.