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Course 14 · Lesson 1.3

How to read and test an argument for God

10 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 1.3

What you will learn

  • Rewrite an argument as numbered premises and a conclusion.
  • Distinguish validity from soundness and from persuasiveness.
  • Identify the premise an opponent is most likely to deny.
  • Ask what an argument would show even if it succeeded.

The big idea

To judge an argument for God, put it in numbered steps: premises first, then the conclusion. Then ask two separate questions. Is it valid, meaning that the conclusion follows if the premises are true? Is it sound, meaning that it is valid and the premises are in fact true? Most disagreement concerns the second question. A fair reader also asks what the argument would prove if it worked, and what a reasonable opponent would say in reply.

Key terms

Premise
A statement offered as a reason for the conclusion of an argument.
Conclusion
The statement an argument tries to establish.
Valid
Describing an argument whose form guarantees that if the premises are true, the conclusion must be true.
Sound
Describing an argument that is valid and has all true premises.
Begging the question
Assuming in a premise the very thing the argument is supposed to prove.
Deductive argument
An argument meant to make the conclusion certain if the premises are true.
Inductive or abductive argument
An argument meant to make the conclusion probable or the best explanation, without making it certain.
Cumulative case
A reasoned case made from several pieces of evidence that support one conclusion together, though no single piece suffices.

Background

The vocabulary of validity and soundness comes from logic as it has been taught since Aristotle. If you have taken Course 10 you have met it. If not, the key point is simple: an argument can be badly built even when its conclusion is true, and well built even when its conclusion is false. The first is the case of someone who reaches a true result by a bad route. The second is the case of someone who reasons correctly from a false premise.

Arguments for God come in different kinds. The ontological argument is deductive and meant to be a priori, that is, it uses reasoning alone without observation. The cosmological and teleological arguments start from some observed feature of the world. Some modern defenders, such as Richard Swinburne, present them as inductive or probabilistic and combine them in a cumulative case. This changes how they should be tested.

Step-by-step explanation

Step 1: Number the premises

Write the argument as a list. For example: 1. Whatever begins to exist has a cause. 2. The universe began to exist. 3. Therefore the universe has a cause. Writing it this way shows what is being claimed. Many arguments sound impressive until their premises are stated plainly.

Step 2: Check validity

Ask whether the conclusion would have to be true if the premises were true. Test by imagining the premises true and the conclusion false. If you can do so without contradiction, the argument is invalid. Most classic arguments for God are valid as stated. Their weakness, when they have one, lies in a premise.

Watch for hidden steps. Sometimes an argument seems to leap from “a first cause exists” to “God exists.” The second statement carries much more than the first, and the missing steps must be supplied.

Step 3: Find the contested premise

For each argument, find the premise that a reasonable opponent would deny first. In the kalam argument it is usually the claim that the universe began. In the argument from contingency it is the principle that every contingent fact has an explanation. In the ontological argument it may be that existence in reality is greater than existence in thought. Naming this premise is the single most useful habit in the course.

Step 4: Ask what supports the premise

A premise can be supported by experience, by science, by an intuition that most people share, or by another argument. Be honest about which. If the support is only that the premise seems obvious, say so. An intuition that seems obvious to one person may not to another, and intuitions can be shaped by upbringing.

Step 5: Ask what the argument shows if it works

Suppose all premises are granted. What kind of being is shown? A cause? A designer? A necessary being? Is it one or many? Is it good or personal? Usually the answer is smaller than the whole of Christian belief, and sometimes smaller than the hopes of the person using the argument. A fair reader records this without scorn and without exaggeration.

Step 6: State the best reply, then the best answer to it

Write the strongest objection in words its holder would accept. Then write the best defender’s response. If you cannot state either side so that a supporter would nod, keep reading. Only then judge.

  1. Can you state the argument in no more than five numbered lines?
  2. Which premise do you find least certain, and why?
  3. Is the argument deductive, or does it aim only at probability?
  4. Does any premise already assume the conclusion?
  5. What would a thoughtful opponent say about the weakest premise?
  6. If the argument succeeded, what exactly would it show?

Examples

A valid but unsound argument

1. All birds can fly. 2. A penguin is a bird. 3. Therefore a penguin can fly. The reasoning is valid, but the first premise is false, so the argument is not sound. This is a standard textbook illustration.

A true conclusion, a poor argument

Someone says: God exists, because many people believe it. The conclusion may be true, but the argument does not support it, since the number of people holding a belief is not by itself a good reason that it is true.

Begging the question

1. The Bible is the word of God. 2. The Bible says God exists. 3. So God exists. The first premise already assumes God exists, so the argument offers no independent reason. Such an argument may express faith but cannot persuade someone who does not share it.

Different perspectives

Catholic

Catholic teaching and Thomistic philosophy hold that sound reasoning from the world can reach God, and the tradition trains students in logic for this reason. Catholic philosophers also stress that arguments do not replace faith, which is a gift of grace.

Orthodox

Orthodox theology respects reason but denies that God is a conclusion. Many Orthodox writers use argument mostly to clear away objections, while insisting that the knowledge of God comes through worship, ascetic life and the sacraments.

Protestant (evidentialist)

Many Protestant apologists, including Swinburne and Craig, hold that belief in God should be supported by good evidence and that the arguments provide it. They take the standards of ordinary reasoning as the right measure.

Protestant (Reformed epistemology)

Plantinga and others argue that belief in God can be properly basic, rational without being based on an argument, much as belief in other minds or in the past is rational without proof. On this view, the arguments are welcome but not required.

Skeptical and secular views

Skeptics often hold that the burden of proof lies on the one asserting that God exists, and that an argument fails if one premise is doubtful. They add that arguments with controversial premises persuade mostly those who already believe.

Why it matters

Careful reading is a skill that serves in every part of life, from politics to medicine. In this field it also protects against two temptations: accepting an argument because its conclusion is comforting, and rejecting it because its conclusion is unwelcome.

Common misunderstandings

Misunderstanding: A valid argument must have a true conclusion.

Correction: Validity only says that the conclusion follows if the premises are true. A valid argument with a false premise may have a false conclusion.

Misunderstanding: If a reader cannot find the flaw in an argument, it must be sound.

Correction: Failing to find a flaw may show only that more study is needed. Philosophers have taken centuries to diagnose errors in some arguments.

Misunderstanding: A premise that most people accept is therefore true.

Correction: Popularity is not proof. Intuitions are evidence of a modest kind, and the strength of the evidence depends on how widely and why they are shared.

Misunderstanding: Showing a premise is uncertain refutes the argument.

Correction: It shows the argument is not compelling. A premise can be uncertain and still be more plausible than its denial.

Knowledge check

What is the difference between a valid and a sound argument?

A valid argument is one in which the conclusion must be true if the premises are true. A sound argument is valid and also has true premises. An argument can be valid and unsound, if a premise is false. When people disagree about an argument for God, they usually dispute whether the premises are true.

What does it mean to beg the question?

It means to assume, in a premise, the very thing the argument is meant to prove. The argument then offers no independent reason for its conclusion. For example, assuming that the Bible is God’s word in order to prove that God exists. The argument may still be sincere, but it cannot persuade someone who does not already accept it.

Why is it useful to find the contested premise?

It shows where the real disagreement lies. Most classic arguments are valid, so the dispute focuses on one premise, such as the claim that the universe began. Naming it lets a reader judge the evidence for the premise instead of arguing about the whole. It also prevents unfair summaries.

Why ask what an argument would show if it succeeded?

Because the conclusions are often smaller than the hopes of those using them. A successful cosmological argument may show a first cause, not the Trinity. Knowing this prevents overclaiming by defenders and also prevents critics from dismissing the argument for failing to prove what it never claimed to prove.

Think it through

  1. Which kind of premise do you tend to trust most: scientific, logical or intuitive?
  2. Have you ever changed your mind because of an argument? What changed?
  3. Is it fair to ask that an argument for God be held to a higher standard than other arguments?
  4. What is the difference between rejecting an argument and rejecting its conclusion?

Independent assignment

Reconstruct an argument

In your own notebook, write 300 to 450 words. Choose one argument for God that you already know, from a sermon, a book or a conversation. Write it in numbered premises with a conclusion. Say whether it is valid. Circle the premise you find weakest and write a paragraph on why. End by writing what the argument would show if it worked. Do not send this to anyone.

Further study