Objection 1: It seems that the separate human soul can move bodies at least locally. For a body naturally obeys a spiritual substance as to local motion, as stated above (Q, A). But the separate soul is a spiritual substance. Therefore it can move exterior bodies by its command.
Objection 2: Further, in the Itinerary of Clement it is said in the narrative of Nicetas to Peter, that Simon Magus, by sorcery retained power over the soul of a child that he had slain, and that through this soul he worked magical wonders. But this could not have been without some corporeal change at least as to place. Therefore, the separate soul has the power to move bodies locally.
On the contrary, the Philosopher says (De Anima i, 3) that the soul cannot move any other body whatsoever but its own.
I answer that, The separate soul cannot by its natural power move a body. For it is manifest that, even while the soul is united to the body, it does not move the body except as endowed with life: so that if one of the members become lifeless, it does not obey the soul as to local motion. Now it is also manifest that no body is quickened by the separate soul. Therefore within the limits of its natural power the separate soul cannot command the obedience of a body; though, by the power of God, it can exceed those limits.
Reply to Objection 1: There are certain spiritual substances whose powers are not determinate to certain bodies; such are the angels who are naturally unfettered by a body; consequently various bodies may obey them as to movement. But if the motive power of a separate substance is naturally determinate to move a certain body, that substance will not be able to move a body of higher degree, but only one of lower degree: thus according to philosophers the mover of the lower heaven cannot move the higher heaven. Wherefore, since the soul is by its nature determinate to move the body of which it is the form, it cannot by its natural power move any other body.
Reply to Objection 2: As Augustine (De Civ. Dei x, 11) and Chrysostom (Hom. xxviii in Matt.) say, the demons often pretend to be the souls of the dead, in order to confirm the error of heathen superstition. It is therefore credible that Simon Magus was deceived by some demon who pretended to be the soul of the child whom the magician had slain.