Thank you for subscribing to Annotated Thomist...check back each day for a new section of St. Thomas' corpus, annotated and summarized. (FREE TRIAL FOR NEW SUBSCRIBERS!!!)
If you need more personalized help reading the Summa, I am available for 1-on-1 sessions, here.
Movement: We must be clear what we mean by "motion." Most think of motion in a purely locative sense of "going from one place to another place." While this is certainly a type of movement, we mean the term in a more general sense. Rather, St. Thomas generally means "any transition, successive or instantaneous, from potency to act." It could be a local movement (how we think of movement), a quantitative movement (growth in size), a qualitative movement (change in the qualities of a thing, e.g., going from hot to cold), or spiritual (movement of the intellect). Thus, we can formulative a nominal and a real definition. The nominal definition is a "passage from potency to act." The real definition is "the act of what is being actualized as it is being actualized."
Moved thing: That thing which moves from "can-be" to "does-be," i.e., what is undergoing a change from potency to act. E.g., "intellect is undergoing movement while it is passing from understanding the premises (when it is only understanding the premisses, it is only potentially, and virtually, understanding the conclusion) to understanding the conclusion."
Mover: The mover is the agent of bringing about movement in a moved thing. Technically speaking, the mover is the proper efficient cause of movement.