Someone suggested that we not mention "causation" since Newton's Third
Law tells us that the forces between two bodies are simultaneous, and
that causation implies temporal sequence. Yet if I am standing at the
chalkboard and decide to cross the room to look at a student's work, my
body must change its state of motion from rest to moving at more-or-less
constant speed across the room. The implied acceleration of my body
must be due to an external force acting on my body, viz., frictional
force exerted by the floor on the sole of my shoe, which force is the
reaction to my foot having thrust against the floor. While these forces
are simultaneous, there is no doubt that my volitional thrust against
the floor is causative ultimately of my acceleration. (One need not
descend into the murky metaphysics of mind-body duality, the existence
or non-existence of free-will, etc., all of which precedes volition,
however one may wish to dissect that.)
Peter Vajk
St.Joseph Notre Dame High School
Alameda, CA 94501