Free Will: Medieval Spirit-Matter Hierarchy
I've not yet found Dr. Thomas Pink's explicit reason for seemingly treating mental acts and physical acts as the same sort of activity, but it seems to be a post-Hobbesian formulation in which the will is not a distinct, spiritual 'substance' but also, in some sense, 'material'.
Dr. Pink notes the difference in the free will problem for Medieval philosophy:
The medievals' belief in the immateriality of decision-making prevented them from seeing the free will problem as we do -- as mainly a problem about how to reconcile freedom with the likelihood that actions are events within a physical world, subject like events of any other kind to physical causation. Instead, the medievals generally saw the world as a cosmic hierarchy -- a hierarchy in which spirit or the immaterial outranked matter. And because spirit or the immaterial outranked matter, immaterial processes, processes such as reasoning or deliberate human action, could not be determined or necessitated by physical or material causes. (Pink, Free Will: A Very Short Introduction, Oxford: Oxford University Press, 2004, page 40)Interesting. The medievals were 'blind' to the mind-body problem that we moderns see whenever we investigate the possibility of free will, for they saw spirit as intrinsically superior to matter and thus necessarily to be obeyed by matter . . . as a matter of course, one might put it. A bit like a lord commanding a knight to enter the field of battle. The knight obeys out of a sense of duty legitimated by a medieval hierarchy in which a lord outranks a knight. Understanding that -- for the medievals -- posed no 'interaction' problem.
The medieval free will problem lay solely in reconciling the free will of humans with the omniscience and providence of God.