See the first post in this series for an explanation and guide of our tour of Summa Contra Gentiles.
We have reached at long last the happiest part of our journey. A proof for the existence of God. Aquinas starts and ends with the best, an argument which, once it is understood, grasped at its full, is fully convincing. It is a scientific proof. It is based on the indisputable evidence of our long observation of Nature. It first saw print, as so much foundational knowledge has does, with Aristotle. So strongly does Aquinas feel about this argument that he offers no other in this work. It is an argument, or rather two arguments which share much in common, which he, and which I think you will agree, is best suited for those of a scientific mind. Read all three (short) paragraphs from Aquinas before reading the footnotes.
Chapter 13: Arguments in proof of God’s existence
1 HAVING shown then that it is not futile to endeavour to prove the existence of God, we may proceed to set forth the reasons whereby both philosophers and Catholic doctors have proved that there is a God.
2 In the first place we shall give the arguments by which Aristotle sets out to prove God’s existence: and he aims at proving this from the point of view of movement, in two ways.i
3 The first way is as follows. Whatever is in motion is moved by another: and it is clear to the sense that something, the sun for instance, is in motion.ii Therefore it is set in motion by something else moving it. Now that which moves it is itself either moved or not. If it be not moved, then the point is proved that we must needs postulate an immovable mover: and this we call God. If, however, it be moved, it is moved by another mover. Either, therefore, we must proceed to infinity, or we must come to an immovable mover. But it is not possible to proceed to infinity. Therefore it is necessary to postulate an immovable mover.iii
4 This argument contains two propositions that need to be proved: namely that whatever is in motion is moved by another, and that it is not possible to proceed to infinity in movers and things moved.iv
iThere are various kinds of movement, change, or evolution that first must be understood. There is movement in space, where an object is first here then there, or a change in orientation. There can be change in mass, where an object excretes or accretes. There can be change in energy, such as when a field offers up a newly created particle from a “quantum fluctuation,” or when mass is converted to energy. There can be change in qualitative characteristics, such as in color. In short, any differentiation whatsoever in an object can be considered change or motion. There need not be, of course, any person to witness or measure this differentiation, nor do we need to understand all of the (secondary efficient) causes that bring this differentiation about. Somebody with no knowledge of internal combustion engines is surely aware that a car moves from one place to another.
iiFor bookkeeping, and for commenting, label the first argument “W1”, for “Way 1”, etc.
We begin with the observation that things move, that they change. There can be no doubt about this. Even those who profess complete philosophical skepticism know that their minds change (about objects moving). (I say “profess” because however much somebody might claim to be a skeptic, nobody except possibly the genuinely insane actually believes it. If you argue with me, you necessarily agree with me. But this point is not in the least necessary for us to continue. Feel free to pretend your computer is not really there.)
And what around us does not change? All of Nature, i.e. the physical, does. Trees rot, even protons decay, babies are born, the universe expands. What remains motionless? Well, truth. Mathematical truths are not subject to movement, neither can logical truths shift from place to place or grow hair. Our knowledge of such truths, individually and collectively, surely evolves, or devolves, as the case may be. But the truths themselves are incorruptible. Again, if you disagree, you agree. If you say, “All truths are inventions”, you have either stated a truth or an invention. If it is a truth, your proposition is self-defeating. If it is an invention, there is no reason to trust it. There is no way to speak coherently except by admitting truth exists and is unchangeable.
Anyway, that much is background. Aquinas is not claiming nothing is unchangeable. His first simple indubitable plain commonsensical premise is only that some things move, and that we all see this to be the case, as for example the relative motion of the sun or your finger on the scroll bar. This is all you must advert to now. Do you?
iiiNow W1 will be proved bit by bit. Aquinas will give examples and clarifications of each of the propositions and premises which comprise the argument and when he is finished no loose ends will remain. However, it is well here to ensure you grasp the intention or meaning of this argument before continuing. Here is a sketch.
Take an analogy—an analogy, I say—from Fulton Sheen. You see a boxcar of a train pass by. It moves. Something caused it to move. What? Well, the boxcar in front of it pulls it. But what caused that boxcar to move? The one in front of it. But this cannot go on forever. We cannot have an infinity of boxcars, each pulled by the one in front. At the start of the line there must exist an engine which pulls all along, or there can be no movement.
The same analogy holds for cogs in a machine. This one moves by the one before it, and so on, a series which must terminate at an axle hooked to a motor. There must be a start.
These are only analogies because we left off short. Something is causing the engine to move, and something is causing the motor to spin. These causes are operating now, in this moment. And this what we’re talking about. Movement or change occurring the here in the right now, at this instant.
The classic example is a stick pushing a stone. Imagine yourself holding the stick and applying steady pressure to it, nudging the stone. The stone moves because of the stick. The stone moves now, in this moment because of the stick’s pressure. The stick is also in motion: it has force now, in this moment applied to it via your arm. Your arm is also in motion: its muscles contract or extend now, in this moment. This is happening all at once, at the same instant. Do not let this slip from your mind.
The muscles are also in motion: individual cells contract or extend now, in this moment. The materials in the cell are also in motion: chemicals are moving or reacting now, in this moment. The chemicals are also in motion: the chemicals subcomponents are moving or reacting now, in this moment; and if the chemicals are simple, the electrons in its shell and the neutrons and protons in its nucleus are moving now, in this moment. And the electrons themselves, and the quarks inside the nucleus are moving now, in this moment.
Again, all this is happening at once. Not in the distant past, but right now.
The quarks are also in motion: the strings, or whatever, inside the quarks now, in this moment are also “vibrating”.
Are there things “bellow” strings, or whatever? I don’t know. It doesn’t matter. What does is that if there is, whatever these objects are, have to be in motion now, in this moment too. The chain of all these objects pushes along, as it were, pushed from “below,” all at the same time. This series cannot, however, continue to infinity. There cannot an infinite number of things smaller, or rather more base, than strings and which must first move before any movement is possible.
There must be a base. There must be a thing which moves, which is itself not moved, and is indeed immovable. There must be a start to everything, a first unmoving mover. If there were not, nothing would ever happen. And we have already agreed things happen.
Now two happy things follow from this. The first (and the proof of this is coming: this is not here a proof, but a claim: do not say it was not proved when it is not claimed as being proved) is that this unmoved mover is and must be the same everywhere and for all changes. That is why the unmoved mover is God.
The second is that to be truly scientific, to honestly understand physics, to speak properly of causation and how the universe is run, one must understand God. Because He is there, at base, in everything. He is the root cause of every single thing that happens. This should be cheering, not the least because of the good news we have received some two thousand years ago, but because our task of contemplating the world is proven finite. There must come a point below which physics ends and God begins, to speak loosely. It is not clear if we will ever figure out the whole of mechanics, though. All we have proved is that the causal movement-chain must be finite. We haven’t any idea, through arguments of this kind, how long it is. Finite does not imply short.
ivCall these P1 and P2, or properly W1P1, etc. Next time we start with these same premises. They are given here for the sole reason of noting that there was only one thing proved in this post. That we see some things move. Everything else was a clarification, a heads up. The argument for God being the unmoved Mover was merely sketched. There is thus no point whatsoever in claiming that the main argument was found wanting because it hasn’t yet been fully given.
Clever readers will also have recognized that at no point was scripture invoked. No divine revelation, other than the ordinary kind, i.e. the revelations of our senses, is assumed. Like I said up top, this proof is purely scientific.
 7 Phys. i.