## The Second Way and Classical physics

-The First Way predicts that physics will only seem complete if it makes the first mover of things non-physical. And so the attempt to make physics a complete causal account leads us to the strange ontology of impetus, forces, momentum and energy, which come to be viewed as a sort of motive substance passed from one thing to another while remaining forever unchanged of itself. They are not the activities of anything, but a sort of subsistent activity. That all motion rests on subsistent activity is correct, but we’re (rightly) embarrassed to articulate what the ontology of energy as subsistent would have to be.

-That activity reduces to subsistent activity is the conclusion of the Second Way. In Physical things, action is always interaction, and activity of efficient causality always exists in the interface between the agent and what it acts upon. Something pushes only so far as it is resisted (otherwise, the two things just float along in contact) and so too with pulling, twisting, pressing, and any other action of a physical agent cause. Transitive powers exist not just by imparting act but in being resisted. If the stone did not press back on your hand, you couldn’t push it.

-Here we hit Newton’s Third Law – the example just given was simply taken from Newton’s own account of the law. The problem is that if the activity really exists co-dependently on an active and resistant force: activity could never result in action. The reaction is always equal to the action, for there is in fact only one action and one force. It is just this equality that is so puzzling, since we don’t see a stasis of equality but an overcoming by the stronger. How can a reaction be always equal to an action but sometimes overcome by it, i.e. be unequal to it?

-Minimally, we have to introduce some causal power into the equation that is not an interactive one, and thus not a natural one. Here we discover yet another way in which the “interaction problem” is profoundly misguided – a purely interactive set of movers would never succeed in moving anything.

-Lets look closer at this point, which modern physics only intensifies. Say that an object the size of the solar system collides with an object the size of a golf ball. As any physicist would tell you, it makes no difference if you view the golf ball at rest and hit by the big thing, or vice-versa. And yet there is some sort of overcoming involved in the action: the golf ball sized thing impedes and even shifts the other by some amount, and vice versa. But there is no warrant in this overcoming in the interaction itself: we might just as well assume one was not overcome at all or even that it moved. The physics would stay the same if we held one body to be absolutely rigid and the other absolutely elastic.

-Overcoming adds something to interaction, and there is overcoming in nature but only interaction in efficient causes or forces.