Aquinas’ Five Ways: What They Prove and Where They Stop

Aquinas' Five Ways are the five short arguments for God's existence that Thomas Aquinas set out in the Summa Theologiae (I, q. 2, a. 3): from motion, from efficient causes, from possibility and necessity, from degrees of perfection, and from the governance of the world. Each reasons from something we observe to a first source that receives nothing from another, and each ends with a line such as "this everyone understands to be God."

That closing line, more than the famous regress, is where the debate now centres. Below we set out each argument from the text, the case against them at full strength, the rival defences, and where the Many Beings series lands among accounts of the attributes of God.

Key takeaways

• The Ways argue from effects. God's existence, for Aquinas, "can be demonstrated from those of His effects which are known to us."
• They argue from present dependence, not a first moment. Aquinas allowed a world without beginning and still found a first cause.
• The weak point is the last line. Reaching God from a first mover depends on how words cross from creatures to Him.
• Every defence pays a price. Thomist, Scotist, inductive and kalam readings each strain somewhere.
• Frame-Indexed Classical Theism (FICT) keeps all five conclusions. Where Thomist analogy leaves its rule unstated and Scotist univocity narrows the gap between Creator and creature, it reads the five as routes to one being that is not an effect.

What are Aquinas' Five Ways?

The Five Ways are the answer to the third article of the second question of the Summa Theologiae, and Aquinas opens them without ceremony: "The existence of God can be proved in five ways." The first three are usually classed as cosmological arguments, reasoning from the existence and activity of the world to its source. The fifth is, in the Stanford Encyclopedia's phrase, the design argument "in extremely clipped form." Their materials, as Wikipedia's survey notes, "draw mainly on the ideas of the philosophers Aristotle and Avicenna."

Behind them stands an earlier question: can God's existence be demonstrated at all? Aquinas answers that it cannot be shown from what God is, since we do not grasp His essence, but it can be shown from what He does. "Hence the existence of God, in so far as it is not self-evident to us, can be demonstrated from those of His effects which are known to us." His warrant is Paul, whom he cites in his own rendering: "The invisible things of Him are clearly seen, being understood by the things that are made" (Romans 1:20).

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If God can be known from His effects, then reason has real work to do before revelation speaks, and words learned from creatures can be truly said of the Creator. If He cannot, we are left either with faith that has no reasons or with words that mean nothing when we say them of God. Aquinas faced both objections in the same article: the evil in the world, which the article on why God allows suffering takes up, and the claim that "everything we see in the world can be accounted for by other principles, supposing God did not exist."

Volume One sets out the foundations this article builds on, and you can read it free.

What do the five ways Aquinas gives actually argue?

The First Way, from motion. Aquinas calls it "the first and more manifest way." Motion in his sense is any change, for "motion is nothing else than the reduction of something from potentiality to actuality," and nothing passes from potential to actual except by something already actual. His example is fire and wood: "that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot." Nothing can be both mover and moved in the same respect, so whatever is moved is moved by another. The series of movers "cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand." So there is a first mover, moved by no other, "and this everyone understands to be God." Its ancestor is Aristotle's unmoved mover, and its vocabulary is that of pure act.

The Second Way, from efficient causes. "In the world of sense we find there is an order of efficient causes," and nothing causes itself. In such an order the first causes the intermediate and the intermediate the last, and "to take away the cause is to take away the effect." Without a first there would be no intermediate and no last, so there is "a first efficient cause, to which everyone gives the name of God."

The Third Way, from possibility and necessity. Some things come to be and pass away. If everything were like that, Aquinas reasons, at some time there would have been nothing, and nothing would exist now. So something exists necessarily, and the series of things necessary through another cannot run on forever. There must be "some being having of itself its own necessity, and not receiving it from another." The argument from contingency treats this Way in full, including its much-disputed middle step.

The Fourth Way, from gradation. "Among beings there are some more and some less good, true, noble and the like." More and less are measured against a maximum, and the maximum in a kind is the cause of everything in it, "as fire, which is the maximum heat, is the cause of all hot things," so "there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God." This Way leans hardest on the Platonic idea that the lesser shares in the greater.

The Fifth Way, from governance. "We see that things which lack intelligence, such as natural bodies, act for an end," acting "always, or nearly always, in the same way." What lacks intelligence cannot tend toward an end unless it is directed, "as the arrow is shot to its mark by the archer." So "some intelligent being exists by whom all natural things are directed to their end." The psalmist sings the same order: "The heavens declare the glory of God; the skies proclaim the work of his hands" (Psalm 19:1, NIV).

Each volume in the series begins from the God these arguments reach.

What is the strongest case against the Five Ways?

The first objection asks why the chain must stop. A series of movers or causes, the critic says, could run back forever, each member explained by the one before it. David Hume, as the Stanford Encyclopedia reports, went further and attacked both the picture of causation as a real, productive power and the principle that every contingent thing has a cause.

The Fourth Way meets a sharper version of the same doubt. That some things are taller than others does not show that something is tallest, still less that the tallest causes all height, so the move from "more and less" to a maximum looks like an inference only a Platonist would grant.

The second objection says the science has moved on. Since Newton, a body moving uniformly needs no mover to keep it going, so the First Way seems to rest on discarded physics. The Fifth Way is read as Paley's watchmaker, and Darwin is thought to have shown that natural selection, not a designer, produces the appearance of purpose. Richard Dawkins put the popular verdict bluntly: the five "proofs" "don't prove anything, and are easily … exposed as vacuous."

The third objection is the strongest, because it grants everything the first two deny. Suppose there is a first mover. Why is it God? The Stanford Encyclopedia's entry on Thomas Aquinas states the problem fairly: "to demonstrate the existence of a prime mover falls well short of demonstrating the existence of a being worthy of being called God. For all we have seen so far, for instance, this first cause might itself be a body." Immanuel Kant, in the encyclopedia's summary, contended that the cosmological argument, "in identifying the necessary being as the most real being, relies on the ontological argument," which he had already rejected. Richard Swinburne, in Wikipedia's summary, judged the arguments "only strong when collected together."

Put at full strength, the case becomes a dilemma. If the Ways reason backward in time to a first moment, they rest on a premise Aquinas himself denied could be proved. If they reason instead about what holds things in being now, the critic presses two questions. Why must that dependence end in one being rather than in five, or in the universe itself? And why should the words "mover," "cause" and "good," learned from creatures, mean anything at all when they arrive at God?

How do Thomists, Scotists and their rivals defend the Five Ways?

The Thomist reply answers the regress with a distinction Aquinas drew himself. Some series of causes are accidental: a man begets a son who begets a son, and the grandfather may be long dead. Others are essential, each member acting only while the one above it acts, as hand, stick and stone. Aquinas allows the first kind to be infinite and forbids only the second: "it is not impossible for a man to be generated by man to infinity; but such a thing would be impossible if the generation of this man depended upon this man, and on an elementary body, and on the sun, and so on to infinity." Commentators, the Stanford Encyclopedia notes, "generally agree that what Aquinas means to exclude is an infinite series of simultaneous causes, a 'vertical' series," and its entry on the cosmological argument quotes Caleb Cohoe's judgment that Aquinas's account of causality "is closer to contemporary theories of ontological dependence than it is to the predominant contemporary theories of causality."

Since motion means any passage from potential to actual, inertia does not touch the First Way, and the Fifth concerns the regular tending of natural things toward ends, not contrivance like a watch. Nor does Aquinas think the work is finished at the end of the article. The questions that follow argue that the first cause is not a body, is entirely simple, perfect, the highest good, infinite, omnipresent, unchangeable, eternal, supremely one and perfectly knowing, and the Stanford Encyclopedia concludes: "These results establish the existence of something worthy of being called God." Divine simplicity sits at the centre of that list.

On the Fourth Way the Thomist answers the tallness objection by restricting it: the argument concerns perfections such as being and goodness, which admit no ceiling of their own kind, not quantities such as height. The strain is twofold. The reply depends on the metaphysics of act and potency, which many philosophers reject, and on a doctrine of analogy that, as the article on Thomism shows, does not state its own rule.

The Scotist reply rebuilds the proof. John Duns Scotus gave the distinction between essentially and accidentally ordered causes its classic name. The Stanford Encyclopedia illustrates the essential kind with a golfer: shoulders move arms, arms move the club, and the arms move the club only while the shoulders move them. Scotus ran his argument for a first efficient cause partly through possibility, so that it rests on what is possible rather than on what happens to exist. He also insisted that the concept of being is said of God and creatures in one sense, so that the argument never changes the meaning of its terms. It succeeds in rigour, and it strains at transcendence, because a God reached by univocity of being risks standing in the same class as what He made.

The inductive reply, Swinburne's, treats each Way as raising the probability of theism and the set as a cumulative case. It is modest and hard to refute, and it turns the critic's complaint that each argument is weak alone into a method. Its cost is that it gives up demonstration and usually pictures God as a person very like us, enlarged without limit, the view called theistic personalism.

The kalam reply, associated with al-Ghazali and William Lane Craig, argues not from present dependence but from a beginning: an actual infinite cannot be traversed by successive addition, so the past is finite and the universe has a cause. It succeeds where the past is finite. It strains because the traversal premise is contested, and because Aquinas held that "by no demonstration can it be proved, that the world did not always exist."

Whether creation can contain a completed infinite is the subject of Volume Five.

How does Frame-Indexed Classical Theism read the Five Ways?

Frame-Indexed Classical Theism (FICT) is a research program in analytic theology that resolves classical theological dilemmas by diagnosing them as artifacts of a single formal error: a term carried across two frames, God's and ours, as though it meant the same thing in each. On these arguments it stands with Thomist analogy on the conclusions, grants Scotist univocity its demand for fixed terms, and declines theistic personalism's enlarged person. Its statement sets the position out in one place.

A mover not moved, a cause not caused, a necessity not received, a perfection not shared from above, an intelligence not directed by another: each Way ends at a being that is not an effect. The Many Beings books put that being at the head of their account of God's nature. "God is the Uncaused Cause, the Prime Mover, the one being in all of reality who is not an effect." The tradition's word for that condition is aseity, existence from oneself, and on it the books rest their first claim, that God's nature and ours differ in kind.

Why one such being and not five? Volume Five answers from aseity itself: to exist of oneself is to be bounded by nothing outside oneself, and "there cannot be two such beings, for each would bound the other and neither would then be a se." Aquinas cites the divine name just before the Five Ways, and the words of Scripture sit comfortably with his reading of them: "God said to Moses, 'I AM WHO I AM. This is what you are to say to the Israelites: "I AM has sent me to you."'" (Exodus 3:14, NIV).

With the Thomists, FICT reads the Ways as arguments from what holds the world in being at every moment. Volume Five runs an argument of the same form about the endless ladder of mathematical infinities and gives the image that fits all five: "The links do not hang from one another; each hangs from the same hook, or from nothing." It is also candid about the strength of its own claim: "We claim inference to the best explanation, not demonstration." God is the ground of being, and "He is before all things, and in him all things hold together" (Colossians 1:17, NIV).

The words in each conclusion, mover, cause, good, intelligent, are learned from creatures and said of God from our side, by His effects; as Aquinas puts it, "the names given to God are derived from His effects." FICT states the rule that analogy left unstated. The terms of logic keep one sense across both frames. Terms whose content involves possibility, time, agency or value carry the frame they are said from. Both senses refer to one reality. The univocity article works this out in full, and the first attack below applies it to the Five Ways.

FICT parts from Aquinas only downstream of the Five Ways. Volume One honours Aquinas's account of agency and then names the point of strain: the First Mover who moves the human will, placed with the creature in "a single causal structure." There the sovereignty of God and creaturely freedom are made to share one scale, and Volume One holds them apart by frame.

The full argument is Resolving the Free Will Dilemma, and Volume One is free.

How does this reading of the Five Ways hold up under attack?

We have run thousands of simulated attacks against Frame-Indexed Classical Theism, drawn from academic and peer-reviewed sources. Two bear directly on the Five Ways.

Must words mean the same of God and creatures for the argument to work?

Here's one of those attacks and how the Many Beings framework would address it.

The objection comes from Duns Scotus, in the Ordinatio (book I, distinction 3), and the Stanford Encyclopedia gives its core: Aquinas grants that all our concepts come from creatures, so "where will that analogous concept come from?" An argument that ends "and this is God" must carry its middle term in one sense from premise to conclusion, or it commits the fallacy of equivocation. Aquinas concedes the point: if names were purely equivocal, "from creatures nothing could be known or demonstrated about God at all." But if "first mover" keeps its creaturely sense all the way, God becomes one more mover, the largest member of a class. Either the Ways equivocate, or they make God a creature writ large.

The dilemma leaves out a third option. The logic of the argument keeps one sense throughout, so the inference is valid. The middle term fixes its reference by the effect, and Aquinas says exactly this: "this effect takes the place of the definition of the cause in proof of the cause's existence." "First mover" therefore points to whatever holds the motion in being, as a name can point to what we cannot see. What that cause is in itself is known analogically, and Volume Five words the claim with care: "the finite frame truly knows the one reality, analogically and inexhaustibly." It is Aquinas's own answer, that from effects "we cannot perfectly know God as He is in His essence," with the rule now written down.

Do the Five Ways need an infinite past to be impossible?

Here's one of those attacks and how the Many Beings framework would address it.

This objection is a Thomist one. The kalam premise that an actual infinite cannot be traversed by successive addition, defended by al-Ghazali and Craig, is contested. It also trades on two senses of "completed": a whole held at once, and a series run through to its end. Aquinas himself held that the beginning of the world is known "by faith alone." Any account of God that rests on the traversal premise therefore rests on contested ground.

The Many Beings series does not rest there. Volume Three grounds the finitude of the created order in its contingency, "the primary and decisive ground," because what exists only as sustained by God cannot be a self-standing, beginningless whole. The traversal argument is kept as corroboration that "is not asked to carry the weight alone," and the two senses of "completed" are separated.

That is the logic of the Ways themselves. Aquinas forbids an infinite series of causes "per se" and permits one "accidentally," so his God is reached through what holds things in being now, not through a first page of history. On the route to God, FICT and Aquinas agree. The books go further only in finding the world's finitude as a consequence of its contingency, not as a premise the argument needs.

The beginning of time has its own chapter in Volume Three.

Frequently asked questions

What are the five ways Aquinas gives, in simple terms?

They are five arguments from the world to God. Things change, so there is a first changer. Things are caused, so there is a first cause. Things can fail to exist, so there is a being that exists necessarily of itself. Things are more and less good, so there is a highest good that causes goodness. Natural things act for ends, so an intelligence directs them. Each ends in a being that receives nothing from another.

Which of the Five Ways is the strongest?

Aquinas called the First Way, from motion, "the first and more manifest way," and many Thomists still lead with it. Others prefer the Third, though its claim that if everything could fail to exist then at some time nothing would have existed is its weakest step. The deeper answer is that the Ways share one strength: each argues from present dependence, which survives even an infinite past.

Did Hume and Kant refute the Five Ways?

Not in the form Aquinas gave them. Hume argued, in Wikipedia's summary, that explaining the causes of each member explains everything; that fits a chain stretching back in time, where each member is explained by its predecessor, but the Ways concern causes acting together now, where no intermediate member explains anything by itself. Kant's charge that the argument depends on the ontological argument assumes a being whose necessity is logical, while the Ways need only a being that exists of itself. The question Kant pointed toward, why the first cause is God, remains the live one.

Does evolution refute the Fifth Way?

No. The Fifth Way is not Paley's watch. It argues from the regular tendency of natural things toward ends, "always, or nearly always, in the same way," and natural selection is itself such a regular process. Evolution can explain how living forms arise without touching why nature acts in law-like, end-directed ways at all, which is the Fifth Way's actual starting point.

Do the Five Ways prove the Christian God?

They reach one first, self-existent, intelligent cause, which is the God Scripture names, but not the Trinity, the incarnation or the cross. Aquinas held some truths, the Trinity among them, to be known by revelation alone. Paul followed the same order at Lystra, beginning from creation's witness: "Yet he has not left himself without testimony: He has shown kindness by giving you rain from heaven and crops in their seasons; he provides you with plenty of food and fills your hearts with joy" (Acts 14:17, NIV). The wider survey of evidence for God places the Ways among the other arguments.

Where to go from here

The Five Ways begin as a question about the world and end as a question about language. Aquinas answered the first in five paragraphs; the second has occupied his readers for seven centuries, because "and this everyone understands to be God" is only as strong as the words that carry us there. State the rule for those words, and the Five Ways stand as Aquinas wrote them, conclusions about a God who holds every link of every chain, now.

That is the work the Many Beings series takes on, and it argues the rule from its first axiom rather than assuming it. Volume One is free, and the series carries the method through evil, time, changelessness and the infinite.