5. Thomas’s Understanding of “Motion” in the First Way
St. Thomas doesn’t think you can demonstrate one way or the other whether the world is eternal, but that it was created. It necessarily depends upon a creator God. Our being is being-in-motion. If there is motion, we are not there yet.
Motion = reduction from potentiality to actuality. Trying to demonstrate that potentiality cannot actualize itself. It can only move form potentiality to actuality by something ina state of actuality. Act is always prior to potentiality. A think cannot be potentially and be actually at the same time without violating the principle of non-contradiction. So, something cannot move itself — this would mean it was moving and potentially moving at the same time. Motion is a progression toward some actualization. Anything in motion was put into motion by another. This cannot go into infinity, otherwise the originating effect has no account for itself. Therefore, you need an unmoved mover.
God is not in motion. He is pure act. You need the simultaneous presence of God in order to sustain the present motion of the world. He needs to be present now. If He is taken out of existence, we would cease to be. God is outside of time, sustaining time. He must be outside of time, because time is a measure of change and God is unmovable.