From a comment at Feser’s blog:
[I]f meaning and intentionality are non-material/metaphysical properties of minds, how do they cause and constrain the physical behavior of our bodies? When your non-material mind rationally determines that you want to utilize the argumentative function of language by expressing a sentence using the keyboard of your computer, how does it make your hands do that?
The simplest way to imagine A acting on B is to imagine pushing, pulling, or heating. When you take a closer look at what what these actions amount to, however, you see that they aren’t simply actions of one thing on another, but effects that result from a mixture or interaction of A and B. And so while you wanted to simply think about action, what you ended up visualizing was interaction, which is a very different thing. You wanted to consider a single causal arrow from A to B, and you ended up visualizing B acting on A in addition to this, and a net effect (C) that is something other than either action.
And yet for all that you still have an idea of action. The idea is simpler and more intelligible than interaction – in fact, interaction resolves to action just as molecules reduce to atoms or any compound reality reduces to its constituent parts. But what would be necessary for some A to just act on B? If B is a physical entity, A cannot be, for then we don’t have what we mean by action but a composite multitude of actions. And so an immaterial mind makes, say, hands act by simply acting on them, whereas a hand only “acts” on something by interacting. Even if it is easier for us to imagine the action of a hand on the hammer, upon analysis this is not what we meant to say when we spoke of action.
To put it another way: when Newton says that every action has an equal and opposite reaction, the first use of the word “action” is a logical abstraction, not something that the physical entities do. For the physicist, action just is interaction. Even if one argues that nothing acts, but that there is only interaction, that is, that an action can only occur in a larger interactive complex, it still is impossible to say that it makes no sense to speak of a non-physical action, since this is exactly what is involved in speaking of an action as such. The denial of immaterial beings would also be a denial of action as simply action.