Analysis of any sequence of movers quickly and certainly inevitably gets pretty complex, and so one can’t object that we need to turn to some sort of systematic method or science in order to make any progress identifying the movers. Put in terms of contemporary science, the First Way predicts that whatever physical science claims as an explain motion will either (a) be itself in motion or (b) be immobile, but a purely abstract or universal entity. Examples of (a) are force, energy, momentum, the inertial power of a body and anything else explained by a conservation laws; examples of (b) are physical laws, mathematical entities, absolute space, Tegmarkian or Galilean accounts of the mathematical universe, etc. But (a) entities can’t explain motion but simply take some motion as given and order other motions to it, and (b) entities can’t move anything except as ideas in the mind of something. Either way, we get no explanation of motion, which is exactly what a science of motion would be looking for in the first place. Taken in this sense, the God one concludes to in the First Way is not so much the last entity in a series of movers as he is the first entity after whatever physical analysis ultimately reduce every motion to. Again, it’s not that we count backwards till we hit God, it’s that we recognize that this backwards analysis can only discover entities incapable of answering the question that initiated the backwards analysis in the first place.
Within the context that the First Way articulates, our options are to posit the existence of some supernatural explanation of motion or to abandon the explanation of motion altogether, posting some motion or another as both unexplained and inexplicable, even though all other motions presuppose it. We stop talking about explaining things and insist that we only co-ordinate phenomena with each other. We don’t mean merely that physics does this – the First Way insists that the advance in physics will come to the extent that it realizes it does not explain but only co-ordinates phenomena – but that we start insisting that this is all that can be done. But this traps us in the logical hypocrisy of the liar paradox – our theory of explanation (not our physics) is that explanations are not possible.