Newton defines uniform motion as a state. Many Thomists have balked at this idea, even seeing it as a contradictio in adjecto. “States” describe things that are steady over time, and motion is unintelligible as describing something remaining the same over time. True, “uniformity” is a state, but (a) uniformity describes both the motion and rest, and so to focus on mere uniformity is not at all what Newton means, since it is obvious and uncontroversial that such motionas and rest are uniform like that. and (b) Einstein extended the identity of motion and rest to include non-uniform motions.
One resolution to this is to say that Newton’s “state” is not being opposed to “the dynamic” but as opposed to an activity, that is, to what motion and rest are to living things. An alligator does not rest in the water out of inertia but in an ambush, which is the same reason that it pounces. The living, in other words, unifies rest and motion as two sorts of activity while inert things cannot unify them in this way. But it can unify them as different states. But what does this mean?
It is clear from Newton’s definitions that inertia is what Thomism calls a “secondary cause”. Inertia never initiates motion but only responds to the causal action of something else. Inertia is not existence but resistence, that is, it is not a state existing of itself but a response to the activity of another. If we are right to make inertia a law of inanimate body – and the tremendous explanatory power of assuming this seems to require that we do so – it follows that the inanimate is borrows its rest or motion from the living, and cannot have this as its activity but only as a state.
If we accept this account we can preserve the truth of Aristotle’s account of natural motion while avoiding its insupportable conclusions. Aristotle is right that if any motion at all is natural, then some local motion is natural, and local motion cannot be natural without natural place. But he was wrong to think that natural place had any intrinsic sense when said of the inanimate as such. The inanimate has its motion or rest not of itself in an absolute sense (the way fire tended to an absolute “up” or earth to an absolute “center”) but only by way of borrowing its state from the activity of the living. It is natural for the inanimate both to move and to rest in the same way that it is natural for the living to do so, but the inanimate has this as a participated stasis.
It is really only in this way that either life or freedom is possible. As soon as nature is given an absolute tendency of itself – as soon as inertia initiates as opposed to reacts, or laws initiate things as opposed to describing the progression from a given initial state – then the inanimate is of itself closed to exterior influence and so cannot be an instrument of the living or the free. The “causal closure” of the universe is really a claim for the primacy and closure of the inanimate or physical – which is not at all what inertia or physical laws are describing.