Five Ways (Aquinas)


The Quinque viæ are five logical arguments regarding the existence of God summarized by the 13th-century Catholic philosopher and theologian St. Thomas Aquinas in his book Summa Theologica. They are:
  1. the argument from "first mover";
  2. the argument from causation;
  3. the argument from contingency;
  4. the argument from degree;
  5. the argument from final cause or ends.
Aquinas expands the first of these – God as the "unmoved mover" – in his Summa Contra Gentiles.

Background

Need for demonstration of the existence of God

Aquinas did not think the finite human mind could know what God is directly, therefore God's existence is not self-evident to us.
So instead the proposition God exists must be "demonstrated" from God's effects, which are more known to us.
By the end of each argument, Aquinas' concept of God has only minimal content which he fleshes out through the rest of the Summa theologiae. For example, the general question of whether "God" has a body or is composed of matter is answered in question three, immediately following the Five Ways.
However, Aquinas did not hold that what could be demonstrated philosophically would necessarily provide any of the vital details revealed in Christ and through the Church, quite the reverse. For example, while he would allow that in all creatures there is found the trace of the Trinity yet a trace shows that someone has passed by but not who it is.

Categorization

All five ways are generally considered to be cosmological arguments.
Aquinas omitted various arguments he believed to be insufficient or unsuited, such as the ontological argument made by St. Anselm of Canterbury.

Essential and Accidental Causal Chains

The first two Ways relate to causation. When Aquinas argues that a causal chain cannot be infinitely long, he does not have in mind a chain where each element is a prior event that causes the next event; in other words, he is not arguing for a first event in a sequence. Rather, his argument is that a chain of concurrent or simultaneous effects must be rooted ultimately in a cause capable of generating these effects, and hence for a cause that is first in the hierarchical sense, not the temporal sense.
Aquinas follows the distinction found in Aristotle's Physics 8.5, and developed by Simplicius, Maimonides, and Avicenna that a causal chain may be either accidental or essential
His thinking here relies on what would later be labelled "essentially ordered causal series" by John Duns Scotus.
This is also why Aquinas rejected that reason can prove the universe must have had a beginning in time; for all he knows and can demonstrate the universe could have been 'created from eternity' by the eternal God. He accepts the biblical
doctrine of creation as a truth of faith, not reason.
For a discussion of a causal chain argument that is based on a created beginning, see Kalam cosmological argument.

The Five Ways

Prima Via: The Argument of the Unmoved Mover

Summary

In the world, we can see that at least some things are changing. Whatever is changing is being changed by something else. If that by which it is changing is itself changed, then it too is being changed by something else. But this chain cannot be infinitely long, so there must be something that causes change without itself changing. This everyone understands to be God.

Explanation

Aquinas uses the term "motion" in his argument, but by this he understands any kind of "change", more specifically a transit from potentiality to actuality. Since a potential does not yet exist, it cannot cause itself to exist and can therefore only be brought into existence by something already existing.

Secunda Via: The Argument of the First Cause

Summary

In the world, we can see that things are caused. But it is not possible for something to be the cause of itself because this would entail that it exists prior to itself, which is a contradiction. If that by which it is caused is itself caused, then it too must have a cause. But this cannot be an infinitely long chain, so, there must be a cause which is not itself caused by anything further. This everyone understands to be God.

Explanation

As in the First Way, the causes Aquinas has in mind are not sequential events, but rather simultaneously existing dependency relationships: Aristotle's efficient cause. For example, plant growth depends on sunlight, which depends on gravity, which depends on mass. Aquinas is not arguing for a cause that is first in a sequence, but rather first in a hierarchy: a principal cause, rather than a derivative cause.

Tertia Via: The Argument from Contingency

Summary

In the world we see things that are possible to be and possible not to be. In other words, perishable things. But if everything were contingent and thus capable of going out of existence, then, nothing would exist now. But things clearly do exist now. Therefore, there must be something that is imperishable: a necessary being. This everyone understands to be God.

Explanation

The argument begins with the observation that things around us come into and go out of existence: animals die, buildings are destroyed, etc. But if everything were like this, then, at some time nothing would exist. Some interpreters read Aquinas to mean that assuming an infinite past, all possibilities would be realized and everything would go out of existence. Since this is clearly not the case, then there must be at least one thing that does not have the possibility of going out of existence. However, this explanation seems to involve the fallacy of composition. Moreover, it does not seem to be in keeping with Aquinas' principle that, among natural things, the destruction of one thing is always the generation of another. Alternatively, one could read Aquinas to be arguing as follows: if there is eternal change, so that things are eternally being generated and corrupted, and since an eternal effect requires an eternal cause, then there must exist an eternal agent which can account for the eternity of generation and corruption. To hold the alternative, namely that an infinite series of contingent causes would be able to explain eternal generation and corruption would posit a circular argument: Why is there eternal generation and corruption? Because there is an eternal series of causes which are being generated and corrupted. And why is there an infinite series of causes which are being generated and corrupted? Because there is eternal generation and corruption. Since such an explanation is not acceptable, there must be eternal and necessary being.

Quarta Via: The Argument from Degree

Summary

We see things in the world that vary in degrees of goodness, truth, nobility, etc. For example, well-drawn circles are better than poorly drawn ones, healthy animals are better than sick animals. Moreover, some substances are better than others, since living things are better than non-living things, and animals are better than plants, in testimony of which no one would choose to lose their senses for the sake of having the longevity of a tree. But judging something as being "more" or "less" implies some standard against which it is being judged. For example, in a room full of people of varying heights, at least one must be tallest. Therefore, there is something which is best and most true, and most a being, etc. Aquinas then adds the premise: what is most in a genus is the cause of all else in that genus. From this he deduces that there exists some most-good being which causes goodness in all else, and this everyone understands to be God.

Explanation

The argument is rooted in Aristotle and Plato but its developed form is found in Anselm's Monologion. Although the argument has Platonic influences, Aquinas was not a Platonist and did not believe in the Theory of Forms. Rather, he is arguing that things that only have partial or flawed existence indicate that they are not their own sources of existence, and so must rely on something else as the source of their existence. The argument makes use of the theory of transcendentals: properties of existence. For example, "true" presents an aspect of existence, as any existent thing will be "true" insofar as it is true that it exists. Or "one," insofar as any existent thing will be "one thing."
The premise which seems to cause the most difficulty among interpreters of the fourth way is that the greatest in a genus is the cause of all else in the genus. This premise does not seem to be universally true, and indeed, Aquinas himself thinks that this premise is not always true, but only under certain circumstances: namely, when 1) the lesser things in the genus need a cause, and 2) there is nothing outside the genus which can be the cause. When these two conditions are met, the premise that the greatest in the genus is the cause of all else in that genus holds, since nothing gives what it does not have. Since Aquinas is dealing specifically with transcendentals like being and goodness, and since there is nothing outside the transcendentals, it follows that there is nothing outside the genus which could be a cause. Moreover, if something has less than the maximum being or goodness or truth, then it must not have being or goodness or truth in itself. For example, how could what has circularity itself be less than fully circular? Therefore, whatever has less than the maximum being or goodness or truth must need a cause of their being and goodness and truth.

Quinta Via: Argument from Final Cause or Ends

Summary

We see various non-intelligent objects in the world behaving in regular ways. This cannot be due to chance since then they would not behave with predictable results. So their behavior must be set. But it cannot be set by themselves since they are non-intelligent and have no notion of how to set behavior. Therefore, their behavior must be set by something else, and by implication something that must be intelligent. This everyone understands to be God.

Explanation

This is also known as the Teleological Argument. However, it is not a "Cosmic Watchmaker" argument from design. Instead, as the 1920 Dominican translation puts it, The fifth way is taken from the governance of the world.
The Fifth Way uses Aristotle's final cause. Aristotle argued that a complete explanation of an object will involve knowledge of how it came to be, what material it consists of, how that material is structured, and the specific behaviors associated with the type of thing it is. The concept of final causes involves the concept of dispositions or "ends": a specific goal or aim towards which something strives. For example, acorns regularly develop into oak trees but never into sea lions. The oak tree is the "end" towards which the acorn "points," its disposition, even if it fails to achieve maturity. The aims and goals of intelligent beings is easily explained by the fact that they consciously set those goals for themselves. The implication is that if something has a goal or end towards which it strives, it is either because it is intelligent or because something intelligent is guiding it.
It must be emphasized that this argument is distinct from the design argument associated with William Paley and the Intelligent Design movement. The latter implicitly argue that objects in the world do not have inherent dispositions or ends, but, like Paley's watch, will not naturally have a purpose unless forced to do some outside agency. The latter also focus on complexity and interworking parts as the effect needing explanation, whereas the Fifth Way takes as its starting point any regularity. but an argument from final cause.

Proofs or Ways?

Many scholars and commenters caution against treating the Five Ways as if they were modern logical proofs. This is not to say that examining them in that light is not academically interesting.
Reasons include:

Philosophical

Criticism of the cosmological argument, and hence the first three Ways, emerged in the 18th century by the philosophers David Hume and Immanuel Kant.
Kant argued that our minds give structure to the raw materials of reality and that the world is therefore divided into the phenomenal world, and the noumenal world. Since the cosmological arguments reason from what we experience, and hence the phenomenal world, to an inferred cause, and hence the noumenal world, since the noumenal world lies beyond our knowledge we can never know what's there. Kant also argued that the concept of a necessary being is incoherent, and that the cosmological argument presupposes its coherence, and hence the arguments fail.
Hume argued that since we can conceive of causes and effects as separate, there is no necessary connection between them and therefore we cannot necessarily reason from an observed effect to an inferred cause. Hume also argued that explaining the causes of individual elements explains everything, and therefore there is no need for a cause of the whole of reality.
The 20th-century philosopher of religion Richard Swinburne argued in his book, Simplicity as Evidence of Truth, that these arguments are only strong when collected together, and that individually each of them is weak.
The 20th-century Catholic priest and philosopher Frederick Copleston devoted much of his work to a modern explication and expansion of Aquinas' arguments.
More recently the prominent Thomistic philosopher Edward Feser has argued in his book Aquinas: A Beginner’s Guide that Dawkins, Hume, Kant, and most modern philosophers do not have a correct understanding of Aquinas at all; that the arguments are often difficult to translate into modern terms. He has defended the arguments in a book at length.
Atheist philosopher J.H. Sobel offers objections to the first three Ways by challenging the notion of sustaining efficient causes and a concurrent actualizer of existence. Leading Atheist philosopher Graham Oppy has offered critiques of the arguments in his exchanges with Edward Feser and in his published work.

Popular

Biologist Richard Dawkins' book The God Delusion argues against the Five Ways.
In Why there almost certainly is a God: Doubting Dawkins, philosopher Keith Ward claims that Richard Dawkins mis-stated the five ways, and thus responds with a straw man. For example, for the fifth Way, Dawkins places it in the same position for his criticism as the Watchmaker analogy- when in fact, according to Ward, they are vastly different arguments. Ward defended the utility of the five ways whilst pointing out that they only constitute a proof of God if one first begins with a proposition that the universe can be rationally understood. Nevertheless, he argues that they are useful in allowing us to understand what God will be like given this initial presupposition.
Eastern Orthodox theologian David Bentley Hart says that Dawkins "devoted several pages of The God Delusion to a discussion of the 'Five Ways' of Thomas Aquinas but never thought to avail himself of the services of some scholar of ancient and medieval thought who might have explained them to him... As a result, he not only mistook the Five Ways for Thomas's comprehensive statement on why we should believe in God, which they most definitely are not, but ended up completely misrepresenting the logic of every single one of them, and at the most basic levels." Hart said of Dawkins treatment of Aquinas' arguments that: