Proof for the Existence of God: An argument from a blog. - Part 1

Apologetics · Natural Theology

Proof for the Existence of God

Part One: The Five Ways of St. Thomas Aquinas

Part 1 of 2 · Foundations

In an age that treats faith and reason as enemies, St. Thomas Aquinas showed that rigorous logic can carry the mind to God. His Five Ways remain the most influential arguments for God's existence ever written.

They are also the most misunderstood. Nearly every popular presentation of them, including my own earlier version of this page, gets at least one crucial thing wrong. So before we state the arguments, we have to lay two tools on the table. Without them the Five Ways collapse into strawmen that any competent atheist can knock down in a sentence. With them, the Ways are far harder to answer than most people suppose.

⚙️ Tool One: Act and Potency

Aquinas inherits from Aristotle a distinction that runs underneath everything else. Every real thing is a mix of what it actually is and what it could become.

The Distinction

Act (actus) is the way a thing actually is right now. A cold cup of coffee is actually cold.

Potency (potentia) is a real capacity to be otherwise. That same coffee is potentially hot. It is not potentially a rhinoceros; potency is a real capacity, not mere logical possibility.

The principle: nothing can move itself from potency to act. The coffee cannot heat itself. Whatever is in potency to something must be brought to act by something already in act. You need the stove, which is already hot.

This is what Aquinas means by "motion." Not merely a thing changing location, but any passage from potency to act: water warming, an acorn growing, a mind coming to understand. Change, in the widest sense.

🔗 Tool Two: What Kind of Causal Chain?

Correcting a common error

You have almost certainly heard the Five Ways explained like this: "The violin exists because the luthier made it. The luthier exists because of his parents. His parents exist because of their parents. This can't go back forever, so there must be a First Cause."

This is not Aquinas's argument, and he would have rejected it. Aquinas explicitly held that human reason cannot prove the universe had a beginning in time. In De Aeternitate Mundi he argues that an eternally-existing universe is philosophically possible; we know the world began only because God revealed it. So none of the Five Ways can depend on the impossibility of an infinite regress backward through time.

Worse: fathers-begetting-sons is Aquinas's own example of the kind of series that can run to infinity. The popular illustration teaches the exact opposite of his point.

The distinction that actually matters is not between finite and infinite chains, but between two kinds of causal series.

Accidentally Ordered

Per accidens

A father begets a son; that son grows up and begets his own son. The grandfather can be dead and buried, and the chain continues without him. Each cause has its own independent power to act. The series is strung out through time, and each link, once caused, stands on its own.

Aquinas allows this to be infinite.

Essentially Ordered

Per se

A hand moves a stick; the stick moves a stone. All of it happening right now, simultaneously. The stick has no power of its own to move anything; it moves the stone only because the hand is moving it at this instant. Remove the hand and the whole series stops dead in the same moment.

This cannot be infinite.

Why It Cannot Be Infinite

In a per se series, the intermediate members have no causal power of their own. They are instruments. A stick does not move stones; it transmits a motion it is receiving.

So if every member is an instrument, and there is no first member actually doing the causing, then nothing is happening at all. An infinite line of sticks moves no stones. A boxcar can pull a boxcar which pulls a boxcar, but unless somewhere there is a locomotive, nothing moves, no matter how many boxcars you add. The problem is not the length of the series. It is the absence of a source.

Every one of the Five Ways is about a per se series, operating here and now. Aquinas is not asking what got the universe started long ago. He is asking what is holding it in being and motion at this very moment. That is a question physics does not touch.

✉️ The Five Ways

With those tools in hand, here are the Five Ways as Aquinas gives them in the Summa Theologiae (I, Q.2, A.3). Note that each concludes with a phrase like "and this all men call God." That modesty is deliberate, and we will see why in Part Two.

I The Argument from Motion ex parte motus

Some things in the world are in motion, that is, passing from potency to act. But nothing moves itself from potency to act; whatever is moved is moved by another, by something already in act.

Now consider the movers acting right now. If each mover is itself being moved by another at this same instant, and there is no unmoved mover anywhere in the series, then nothing is actually causing anything, and there would be no motion at all. But there plainly is.

Therefore: there must be a first mover, itself unmoved, with no potency to be actualized. Something that is Pure Act.

II The Argument from Efficient Causality ex ratione causae efficientis

In the world we find an order of efficient causes, causes producing their effects here and now. Nothing can be the efficient cause of itself, since it would have to exist before it existed, which is absurd.

Again the series is per se: think of the causes sustaining a thing in existence at this instant, not a line of ancestors stretching into the past. Take away the first cause and you take away the effect, immediately and entirely.

Therefore: there must be a first efficient cause, itself uncaused, presently holding the whole order of causes in operation.

III The Argument from Contingency ex possibili et necessario

Some things are contingent: they come to be and pass away, and so they are capable of not existing. Your existence hangs on a thousand conditions that might have failed.

But a merely contingent thing does not account for its own existence; it must be given existence by something else. And if everything whatever were of this borrowing kind, with nothing possessing existence in its own right, then there would be nothing to do the giving, and nothing would exist at all. But things do exist.

Therefore: there must be a being that exists necessarily, not by borrowing existence from another, but of its own nature.

IV The Argument from Degrees of Perfection ex gradibus

We find things more and less good, more and less true, more and less noble in being itself. But "more" and "less" are said of things according as they approach in different degrees to something which is the maximum.

This works for what the tradition calls the transcendentals, the perfections that run right across being itself: being, goodness, truth, beauty. These are not measured against some larger member of the same class, but by participation: a thing is good insofar as it shares in goodness. And whatever is had by participation must be traced to something that has it essentially, of itself, not by receiving it.

Therefore: there is something which is to all beings the cause of their being, goodness, and every perfection, possessing these not by participation but by its own essence.

V The Argument from Finality ex gubernatione rerum

This is not the Design Argument

The Fifth Way is constantly confused with William Paley's watchmaker: the argument that living things are so complex and improbable that they must have been assembled by a designer. That is not Aquinas's argument, and the difference matters enormously. Paley argues from complexity, from apparent artifice. That argument is the one Darwin wounded. Aquinas argues from something entirely different, and evolution leaves it wholly untouched.

Aquinas observes that things lacking intelligence nevertheless act toward ends, and do so reliably, by their very nature. Fire heats. An acorn tends toward becoming an oak and never toward becoming a walrus. Electrons behave in regular, end-directed ways. This is not occasional; it is what nature simply does.

But here is the puzzle. An end is a thing that does not yet exist. How can something that does not yet exist direct anything? A thing with a mind can aim at a goal, because it can hold the goal in thought. An acorn holds nothing in thought. Yet it is unmistakably directed.

Nothing can be ordered toward an end unless that end is held in an intellect. The arrow does not aim itself; it flies to the mark because an archer has aimed it.

Therefore: there is an intelligence by which all natural things are directed to their ends. Note carefully that this argument is not weakened one inch if every organism on earth arose by natural selection, because natural selection itself is a lawlike, end-directed process, and the question is why any unintelligent thing behaves lawfully at all.

🎯 What the Five Ways Actually Establish

Be precise here, because both defenders and critics routinely overreach. The Five Ways do not conclude to the Trinity, to the God of Israel, or to Jesus Christ. They conclude to something rather stark:

Unmoved Mover

Pure Act, with no potency to be actualized

First Cause

Uncaused, sustaining all causes now

Necessary Being

Existing of its own nature, not by borrowing

Maximal Perfection

Good, true, and being by essence, not participation

Supreme Intelligence

Ordering all nature to its ends

Aquinas knows this perfectly well. That is exactly why each Way ends not with "and therefore the Blessed Trinity," but with the careful, almost dry phrase, "and this all men call God." He has proven a something, and he has more work to do. The next several dozen questions of the Summa are spent doing it.

On Polytheism

Do the Ways rule out many gods? Yes, but not by the usual bad argument that "the gods would have to move each other."

Aquinas's real argument (ST I, Q.11) runs from simplicity. Suppose there were two such beings. They would have to differ somehow, or they would be the same being. But to differ, one must possess something the other lacks. And what the Ways establish is a being that is Pure Act, lacking nothing whatever. Therefore there cannot be two. There is not room in reality for two infinities.

Continue to Part Two

We have reached an Unmoved Mover, an Uncaused Cause, a Necessary Being. But what is it? And here a serious objection waits: some philosophers argue that the Five Ways only work if you smuggle in a deeper metaphysical premise, the distinction between essence and existence, in which case a single attack could topple all five at once.

Part Two takes up that challenge directly: what kind of demonstration the Five Ways really are, where they point, and why the objection fails.

Part Two: The Five Ways and the Divine Esse →

📚 For Further Reading

• The text itself: Aquinas, Summa Theologiae, I, Q.2, A.3 (the Five Ways), and I, Q.2, A.1–2 (the method, which matters more than most readers realize).
• Matt Fradd and Dr. Robert Delfino, Does God Exist? A Socratic Dialogue on the Five Ways of Saint Thomas Aquinas. The most accessible serious treatment in print.
• Fr. Joseph White, O.P., on contingency, on degrees of perfection, and on modern objections to finality.
• Aquinas, De Aeternitate Mundi, for the argument that reason alone cannot prove the world had a beginning. Essential for seeing why the Ways are not about temporal regress.