Final answer:
The Unmoved Mover argument by St. Thomas Aquinas suggests that everything in motion was set in motion by another entity, leading to the conclusion that there must be a first cause, which is God. This refers to the transition from potentiality to actuality, with motion intended by a purposive nature towards actualization, under the guidance of God.
Step-by-step explanation:
The argument you're referring to is known as St. Thomas Aquinas's Cosmological Argument, or more specifically, the Argument from Motion, which is occasionally called the argument of the Unmoved Mover. Aquinas's argument invokes a series of premises: First, that there exists a series of events or motions; second, that these events exist as caused and not uncaused; third, that there must exist a necessary being that is the cause of all contingent beings; and fourth, that there must be a necessary being that is the cause of the whole series of beings. This leads to the conclusion that the First Cause or Unmoved Mover, which initiated all other motions without itself being moved, is what Aquinas identifies as God.
Aquinas's conceptualization of motion isn't merely limited to physical movement from one place to another, but also encompasses the philosophical notion of moving from a state of potentiality to actuality. For instance, an acorn has the potential to grow into an oak tree, and when it does, it is said to have moved from potentiality to actuality. This change, or 'becoming', is directed by a purpose, which is aligned with Aquinas's belief that God has instilled a directed purpose in all things. In short, within Aquinas's metaphysics, purpose orients the motion of a thing towards its fulfillment or actualization, with God as the initiator and director of all motion.