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Course 14 · Lesson 7.3

Assessing the modal argument: what it needs and what it shows

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 7.3

What you will learn

  • Identify the three places where the modal argument can be questioned.
  • Explain the objection that the possibility premise begs the question.
  • Explain the objection from S5 and from the idea of a necessary being.
  • State what the argument would establish even if it succeeded.

The big idea

The modal ontological argument is valid, so it can be assessed only by testing its premises and its logic. There are three main pressure points: the premise that a maximally great being is possible, the principle S5 which carries possibility to actuality, and the coherence of the concept of maximal greatness itself. The argument also yields a conclusion short of the Christian God. A fair judgment is that it clarifies the debate and shows that the dispute lies in what one takes to be possible.

Key terms

Begging the question
Assuming in a premise what the argument is supposed to prove.
Conceivability
What the mind can coherently picture or describe.
Epistemic possibility
What is possible for all one knows, which may not be possible in fact.
Metaphysical possibility
What could really have been the case, whatever one knows.
Coherent concept
An idea whose parts do not conflict, so that something could in principle answer to it.
Burden of proof
The responsibility to give reasons, resting on the one who makes a claim.

Background

After Plantinga’s argument appeared, philosophers wrote about it from many angles. The analysis here follows the main lines of the discussion without claiming that all philosophers would agree on them. The central lesson is that the argument converts the question of God’s existence into a question about possibility, and then asks whether the possibility can be known.

Two background points help. First, assessing a valid argument is different from catching a fallacy: the reader must decide which premise to doubt and why. Second, the word possible has several senses. What is possible for all anyone knows is not the same as what could really have been. The modal argument needs the second sense, while the evidence offered for it often supports only the first.

Step-by-step explanation

Step 1: The first pressure point, the possibility premise

The argument needs it to be possible that a maximally great being exists. Critics say there is no independent reason to think so. The premise cannot be settled by looking at the world. If a necessary being is possible, it is actual, so to grant its possibility is to grant its existence, and a person who denies God will deny the premise. Therefore the argument is said to beg the question against the atheist.

Defenders reply that this proves too little. A premise can be reasonable to accept even if an opponent denies it. Everyone must decide on grounds that seem good which possibilities are real. They add that there is no evident contradiction in the idea of an all-knowing, all-powerful, good being, and that the burden lies on those who claim there is.

Step 2: Reasons for and against the premise

Reasons offered for the premise include that the concept seems coherent, that many people have conceived of such a being without evident contradiction, and that it is not ruled out by science. Reasons offered against it include the problem of evil, which some say shows that a perfectly good and powerful being is impossible, and arguments that omniscience and omnipotence conflict with other divine attributes, such as being outside time, or with human freedom. Defenders reply to each. If the problem of evil were a decisive argument of impossibility, it would be a much stronger argument than most atheists claim.

Step 3: The second pressure point, S5

The step from possible necessity to necessity depends on S5. Some philosophers doubt S5 for metaphysical possibility. If what is possible in one world differs from what is possible in another, the argument fails. Defenders reply that S5 is the most widely accepted system and fits the idea of necessity as truth in all worlds. The matter is technical and has no agreed answer, but most commentators do not rest their objection here.

Step 4: The third pressure point, the concept

Some argue that the very concept of a necessary existent is confused. Hume and Kant held that no existence claim can be necessary. Others hold that only truths can be necessary, not things. Defenders reply that these objections assume what they must prove, and that abstract objects like numbers may exist necessarily. Whether a concrete being could do so is the question.

Step 5: What the argument would show

If successful, the argument shows a being that is all-knowing, all-powerful and morally perfect, and exists in every world. This is more specific than a first cause but still short of Christianity. It says nothing about the Trinity, the incarnation, or the person of Christ. A Jewish or Muslim theist, or a philosophical theist, could accept it. Defenders say that is as it should be, since Christianity depends on revelation as well as on reason.

Step 6: A balanced verdict

Most philosophers think the argument is valid and not persuasive, because its first premise is no easier to establish than the conclusion. A significant minority think it shows that belief in God is rational. The argument remains a good example of how formal tools sharpen a debate without ending it.

  1. Is the possibility premise something you can know?
  2. Does granting the premise amount to granting the conclusion?
  3. Which would you doubt first: the premise, S5, or the concept?
  4. What do you make of the point that the problem of evil may tell against the premise?
  5. Why is the argument accepted by few philosophers, even though valid?
  6. What would persuade you that a maximally great being is possible?

Examples

The Goldbach conjecture

Mathematicians do not know whether every even number above two is the sum of two primes. If the conjecture is true, it is necessarily true. If false, necessarily false. Yet nobody knows which. This shows that a statement can be possible for all anyone knows without being possible in fact. The same worry applies to the first premise.

Water and H2O

Before chemistry, people could conceive of water not being H2O. Kripke argued that, given that water is H2O, it is necessarily so. So conceivability in ignorance does not show possibility. Critics of the modal argument draw on this to say that conceiving of a maximally great being does not show that one is possible.

The atheist’s premise

An atheist may say that, as far as she can tell, a maximally great being is not possible, given the amount of evil. A theist may say the opposite. Each, according to Plantinga, may be within her rights. The disagreement lies not in logic but in judgments about what could be.

Different perspectives

Catholic

Catholic philosophers who follow Aquinas generally prefer arguments from the world to arguments from the concept of God. Some Catholic thinkers have defended modal arguments, but the Church does not rely on them. The dominant view is that natural reason can know God, though not necessarily by this route.

Orthodox

Orthodox theology holds that God is known beyond argument, in worship. A formal argument that defines God as the greatest among possible beings is foreign to this approach, and the tradition would see it as at most an exercise.

Protestant

Plantinga and Maydole defend the argument. Other Protestant philosophers think it fails to convince but do not doubt its logic. Reformed epistemologists view it as unnecessary for rational faith.

Philosophical views

Oppy’s Ontological Arguments and Belief in God (1995) is a detailed critique. Peter van Inwagen holds that the argument is valid but that its premise is not known to be true. Some defenders argue that the possibility premise has the same status as many accepted philosophical premises.

Skeptical views

Skeptics stress that the argument cannot move a person who does not already think the premise plausible, and that it gives no independent reason to believe that a perfect being could exist. They regard it as a clever restatement of the question.

Why it matters

Assessing a valid argument is a different skill from detecting an invalid one. It requires finding the premise that carries the weight and asking what supports it. This lesson models the skill, which applies to every argument in the course.

Common misunderstandings

Misunderstanding: If the argument is valid, it is a proof.

Correction: A proof needs true premises that a reasonable opponent can accept. Validity alone is not enough.

Misunderstanding: The argument begs the question in an obvious way.

Correction: Whether it does is debated. The charge needs care, since many good arguments have premises that their opponents deny.

Misunderstanding: A rejected argument has no value.

Correction: The argument clarified concepts of necessity and showed how a dispute can be reduced to one premise. Such clarification is a real gain.

Misunderstanding: The argument proves the Christian God.

Correction: At best it supports a maximally great being. The specifically Christian claims lie elsewhere.

Knowledge check

What are the three main pressure points in the modal argument?

They are the premise that a maximally great being is possible, the principle S5 which takes possible necessity to necessity, and the coherence of the concept of a maximally great or necessary being. Most criticism focuses on the first, because granting it amounts to granting the conclusion for one who accepts S5.

Why do critics say the argument begs the question?

Because the first premise, that a necessary being is possible, entails that it exists if S5 holds. An atheist who denies the existence will therefore deny the possibility. Defenders reply that the premise may still be reasonable and that an opponent’s denial needs its own support. The disagreement turns on what counts as a fair premise.

How does the problem of evil bear on the premise?

If a perfectly good, all-powerful being is incompatible with the existence of evil, then such a being is impossible, and the first premise is false. Defenders reply that the problem of evil is not shown to be a logical contradiction, as Plantinga argued in the free will defense, and that at most it lowers the probability.

What does the argument leave undecided?

It leaves undecided whether God is Trinitarian, whether God became incarnate, and whether any particular religion is true. It concerns only a being of maximal excellence. Even defenders treat it as one step in a cumulative case, so that evidence from history and experience must be added for Christian claims.

Think it through

  1. How would you decide between a premise and its reverse?
  2. Is it fair to ask an argument to persuade someone who rejects the premise?
  3. Does an argument have value if it clarifies but does not convince?
  4. What does this lesson suggest about how to read other arguments?

Independent assignment

Testing the pressure points

In your own notebook, write 350 to 500 words. For each of the three pressure points, write the objection in a sentence, the best reply in a sentence, and your own judgment in a sentence. Then write a paragraph stating which objection seems strongest, and what a defender must show to answer it. Do not send this to anyone.

Further study