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Course 14 · Lesson 5.1

From Aquinas’s fifth way to Paley’s watch

9 minute read

Lessons in this course

Course 14 outline

Module 1: Arguments, Existence and Necessity

  1. What natural theology attempts and what it does not
  2. Necessary and contingent existence
  3. How to read and test an argument for God
  4. Philosophy of religion today: a map of the field

Module 2: The Ontological Argument

  1. Anselm and the argument of the Proslogion
  2. Gaunilo and the perfect island objection
  3. Kant: existence is not a real predicate
  4. What the ontological argument would show if it worked

Module 3: Cosmological Arguments

  1. Aquinas: the first three ways
  2. Infinite regress: what is the problem?
  3. Leibniz, the principle of sufficient reason and the argument from contingency
  4. Objections: the brute fact reply and the fallacy of composition

Module 4: The Kalam Cosmological Argument

  1. The kalam tradition: Philoponus, al-Ghazali and Bonaventure
  2. The modern argument: whatever begins to exist has a cause
  3. Did the universe begin? Philosophy and cosmology
  4. Objections and replies, and what follows about the cause

Module 5: Teleological and Fine-Tuning Arguments

  1. From Aquinas’s fifth way to Paley’s watch
  2. Hume and the Dialogues Concerning Natural Religion
  3. Darwin and the change in the design argument
  4. The fine-tuning argument: what is claimed and what is debated
  5. The multiverse and other replies

Module 6: The Moral Argument and Divine Hiddenness

  1. The moral argument: Kant, Lewis and contemporary forms
  2. The Euthyphro question and moral realism without God
  3. Evolution and moral knowledge
  4. The argument from divine hiddenness and Christian replies

Module 7: Contemporary Modal Arguments and Evaluation

  1. Possible worlds and modal logic in plain language
  2. Plantinga’s modal ontological argument
  3. Assessing the modal argument: what it needs and what it shows
  4. Weighing the arguments together, and what none of them prove

All courses

Program / Course 14: Arguments for the Existence of God / Lesson 5.1

What you will learn

  • State Aquinas’s fifth way and explain what he means by governance.
  • State Paley’s argument from the watch and explain how it differs.
  • Distinguish arguments from purpose in nature from arguments from design by analogy.
  • Identify the premise at which each argument is most open to objection.

The big idea

Teleological arguments reason from signs of order and purpose in the world to a mind behind it. Aquinas’s fifth way notes that natural things without knowledge act for an end, as an arrow does when an archer shoots it, and concludes that an intelligence directs them. William Paley, in 1802, compared the living world to a watch that implies a watchmaker. The two arguments are often confused. Aquinas argues from regular goal-directed activity, while Paley argues from complex arrangement that resembles human design.

Key terms

Teleological
Having to do with purpose or end. The Greek word telos means goal or end.
Final cause
In Aristotle, the end for which something happens or exists, such as health for a medicine.
Governance
Aquinas’s term for the direction of things toward their ends by an intelligence.
Argument by analogy
An argument that two things are alike in some ways, so are probably alike in a further way.
Natural Theology (1802)
William Paley’s book, which opens with the watch and goes on to examples from anatomy.
Complex specified arrangement
A pattern of parts arranged to serve a function, as in a watch or an eye.
Bridgewater Treatises
A series of books of the 1830s, funded by a bequest, on the power, wisdom and goodness of God as shown in creation.

Background

Arguments from order in the world are among the oldest. Plato, in the Timaeus, speaks of a divine craftsman. Cicero argued that the order of the heavens shows a mind. Early Christians such as Theophilus of Antioch and Basil used the beauty and order of creation as witness to the Creator. The Bible has a similar thought in Psalm 19, in Job, and in Paul’s letter to the Romans.

Aquinas’s fifth way is the most compact. Paley’s is the most famous. Between them lies a change: the medieval writers worked with an Aristotelian view in which natural things have built-in ends, while early modern science described nature as matter moving by laws, which led later writers to treat the world as a machine made by an engineer.

Step-by-step explanation

Step 1: Aquinas’s fifth way

Aquinas writes that observation shows that things that lack knowledge, such as natural bodies, act for an end. This is clear because they act always or nearly always in the same way to achieve what is best. So they reach their end by design, not by chance. Whatever lacks knowledge cannot move toward an end unless it is directed by something with knowledge and intelligence, as an arrow is directed by an archer. Therefore some intelligent being exists by whom all natural things are directed to their end, and this is what is called God.

Notice that Aquinas does not mention complexity, eyes or watches. His concern is regularity and direction, as when an acorn grows into an oak and not a fish.

Step 2: Paley’s watch

Paley asks the reader to imagine crossing a heath and finding a stone, and then finding a watch. A stone may have lain there forever. A watch, with its parts framed and put together for the purpose of telling time, requires a maker. Paley then turns to nature. The eye, he argues, is more complex than a telescope and shows the same marks of design. Therefore it requires a designer.

The argument is by analogy: natural organisms are like machines made by people, machines have designers, so organisms probably do too.

Step 3: The differences

Aquinas argues from the general fact that things act for ends. Paley argues from particular arrangements of parts. Aquinas does not assume nature is a machine. Paley does. Aquinas’s argument is untouched by the discovery of a natural mechanism for adaptations in the sense that a mechanism is still a regular direction to an end. Paley’s argument is more exposed, since a natural explanation of the arrangement would remove the analogy.

Step 4: Where objectors push

Against Aquinas, objectors say that the premise that things lacking knowledge act for an end is an Aristotelian doctrine that modern science has dropped, since physics explains motion by causes and laws without goals. Thomists reply that laws and regularities themselves need explanation. Against Paley, objectors say that the analogy is weak because living things are not much like watches, and, as the next lessons show, Hume and Darwin raised stronger objections.

Step 5: Why Paley mattered

Paley’s book was a standard text at Cambridge when Charles Darwin studied there, and Darwin read it with admiration. The Bridgewater Treatises carried the argument further in the 1830s. For decades, design was the most popular argument for God in England. The next lessons explain why that changed.

  1. What does it mean to say a natural thing acts for an end?
  2. Is an acorn growing into an oak an example of acting for an end?
  3. How does the watch differ from a stone?
  4. Is a living organism relevantly like a machine?
  5. What does Aquinas’s example of the arrow show?
  6. Which of the two arguments seems stronger to you?

Examples

The acorn

An acorn, given soil and water, grows into an oak and not into a pine. Aristotle and Aquinas see in this a built-in direction toward an end. Modern biologists describe it in terms of genes and chemistry. Whether the older description is still meaningful is part of the debate.

The watch on the heath

Paley’s example remains the best-known image of the argument. He says that even a person who had never seen a watch made would conclude that it had a maker, because its parts are fitted together to a purpose.

The arrow

An arrow flies to a target because an archer aimed it. The arrow has no knowledge, but it hits a goal. Aquinas uses this to show that goal-directed action by something without knowledge points to a mind elsewhere.

Different perspectives

Catholic

The Catholic Church teaches that the order of creation witnesses to the Creator (Catechism, paragraphs 31 to 36, drawing on Romans 1:20). Thomists defend the fifth way as an argument about natural ends, not about complexity, and think Paley’s version is a different argument.

Orthodox

Orthodox writers such as Basil the Great in his Hexaemeron praised the order of creation as a sign of the Creator’s wisdom. They tend to treat this as praise and contemplation, not as an argument, seeing in creation a sign of God’s energies.

Protestant

Paley was an Anglican priest, and design arguments were a mainstay of English Protestant thought. Calvin spoke of the creation as a theater of God’s glory. Barth later rejected natural theology of this kind, and Reformed epistemologists treat the sense of design as a basic belief.

Scholarly views

Historians note that Paley’s argument was not original, since he drew on earlier writers like John Ray and Bernard Nieuwentyt. They also note that Aquinas did not give the argument the pride of place that later writers did.

Skeptical views

Skeptics say the notion of acting for an end is a projection of human intentions on nature. They hold that Paley’s analogy is weak, and that natural processes can produce apparent design without a designer.

Why it matters

Many people hold a vague version of the design argument and do not know which they are holding. Separating the argument from ends and the argument from artifacts makes later discussions of Hume, Darwin and fine-tuning clearer.

Common misunderstandings

Misunderstanding: Aquinas’s fifth way is the same as Paley’s watch.

Correction: It is a different argument. Aquinas argues from natural bodies acting regularly for ends, not from complex arrangement or analogy to machines.

Misunderstanding: Paley argued that the world is a machine.

Correction: He argued by analogy that it is like one in having parts adapted to a function.

Misunderstanding: Design arguments only began in the nineteenth century.

Correction: They date from Plato and Cicero and appear in the Fathers of the Church.

Misunderstanding: Darwin refuted Aquinas’s fifth way.

Correction: Thomists argue that evolution explains how adaptations arise, not why nature is ordered and directed at all. The debate is open.

Knowledge check

State Aquinas’s fifth way in brief.

Things without knowledge, such as natural bodies, act for an end, since they act regularly to achieve what is best. What lacks knowledge cannot direct itself to an end unless directed by something with knowledge, as an arrow by an archer. So an intelligent being exists who directs all natural things to their ends, and this is called God.

How does Paley’s argument work?

He compares a watch found on a heath with a stone. The watch has parts arranged for a purpose, so it must have a maker. Natural things, like the eye, show similar arrangement, even greater, so they must have a maker. The argument works by analogy between organisms and machines.

Why is Paley’s version more exposed to objections?

It depends on the analogy between organisms and artifacts and on the claim that only a designer can explain complex arrangement. If a natural process can produce such arrangement, the analogy loses force. Aquinas’s version concerns regular direction toward ends, which a natural process does not obviously remove.

What is the objection to Aquinas’s premise that natural things act for ends?

Critics say that this is an Aristotelian view abandoned by modern science, which explains events by laws and causes without goals. Thomists reply that regular laws still show direction toward results, and that the regularity itself calls for explanation. The disagreement is over whether final causes are real features of nature.

Think it through

  1. Do you see purpose in nature, or only in human things?
  2. Is a sense of design the same as an argument?
  3. How might the arrow example be challenged?
  4. Why did the argument become so popular in the nineteenth century?

Independent assignment

Two arguments side by side

In your own notebook, write 350 to 500 words. Write Aquinas’s fifth way and Paley’s watch argument as numbered steps in two columns. Mark where they differ. Then write which one you think faces the harder objection, and why. Do not send this to anyone.

Further study