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Course 14 · Lesson 3.3

Leibniz, the principle of sufficient reason and the argument from contingency

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 3.3

What you will learn

  • State the principle of sufficient reason and its main forms.
  • Reconstruct Leibniz’s argument from contingency in numbered steps.
  • Explain why the argument asks about the whole collection of contingent things.
  • Describe the main reasons philosophers have for accepting or doubting the principle.

The big idea

Gottfried Wilhelm Leibniz (1646 to 1716) argued that nothing exists or happens without a sufficient reason, an explanation of why it is so and not otherwise. Applied to the whole world, which is contingent, the principle seems to demand an explanation outside the world, a necessary being. Defenders find the principle a basic assumption of all inquiry. Critics say it is unproven, that it leads to troubling results, and that the universe might simply be a brute fact.

Key terms

Principle of sufficient reason (PSR)
The claim that every truth, or every fact, has an explanation of why it is so.
Brute fact
A fact that has no explanation. It simply is so.
Sufficient reason
An explanation that is enough to account for why something is the case.
Argument from contingency
An argument that the existence of contingent things requires a necessary being as their explanation.
Contingent fact
A fact that could have been otherwise, such as the existence of a particular planet.
Necessary being
A being that exists by its own nature and has no external cause.
On the Ultimate Origination of Things
A short work of Leibniz from 1697 that sets out the argument in clear form. A related text is the Monadology of 1714.

Background

Leibniz was a German philosopher, mathematician and diplomat. He built on medieval cosmological arguments, especially the Muslim form of the argument from contingency in Avicenna, and gave the argument a sharp new formulation. In the Monadology he writes that the sufficient reason for the series of contingent things must lie outside the series, in a necessary substance, which is God.

The principle of sufficient reason has a long history. Parmenides and Plato touch on it. Leibniz considered it one of the two great principles of reasoning, alongside non-contradiction. Spinoza, Leibniz’s contemporary, also held the principle, but concluded that the universe itself is the necessary being, a view different from theism.

Step-by-step explanation

Step 1: The principle

The PSR can be stated in several ways. A strong form says that every fact has an explanation. A weaker form says that every contingent fact has an explanation. Leibniz held the strong form. The weaker form is enough for the argument from contingency.

Step 2: The argument in numbered form

1. Every contingent fact has an explanation. 2. The existence of the world, the whole collection of contingent things, is a contingent fact. 3. So there is an explanation of the existence of the world. 4. The explanation cannot lie in a contingent thing inside the world, since that would be part of what needs explaining. 5. So the explanation lies in something outside the contingent world. 6. That explanation must itself be a necessary being. 7. So a necessary being exists, which is God.

Contemporary defenders such as Alexander Pruss and Robert Koons restate the argument using more carefully worded versions of the PSR.

Step 3: Why the whole collection

Suppose each contingent thing is explained by an earlier one, without end. Each fact is explained, yet the whole series might seem to stand unexplained. Leibniz asks not why this thing exists, but why there is a world of contingent things at all. He argues that no earlier member of the series can answer that question. Even an infinite past is no escape.

Step 4: Why accept the principle?

Defenders say the PSR is presupposed by science and everyday reasoning. When a person finds a strange object in a field, she asks how it got there and does not suppose it has no reason. They add that denying the PSR makes it hard to defend any inference, since an unexplained event could always interrupt a pattern. Some also treat the PSR as simply self-evident on reflection.

Step 5: Why doubt the principle?

Critics reply that scientific practice requires only that scientists look for explanations, not that every fact has one. Quantum physics, on some interpretations, contains events with no determining cause. A further problem was raised by Peter van Inwagen: if every contingent fact has an explanation that is itself necessary, it seems to follow that all facts are necessary, and this collapses the difference between what is and what must be. Defenders have offered replies, but the problem is regarded as serious.

  1. Is the PSR obvious to you, or does it need defense?
  2. What would it be like to live as if some events had no reason?
  3. Does asking why the world exists at all make sense?
  4. How is the PSR different from the claim that every event has a cause?
  5. Does the problem raised by van Inwagen seem decisive to you?
  6. Why might Spinoza and Leibniz accept the same principle and reach different conclusions?

Examples

The endless geometry book

Leibniz asks the reader to imagine a geometry book that had always existed, copied from an earlier copy, and so on without end. Each copy would be explained by the one before. Yet the question why there is such a book at all would remain unanswered by the series. Leibniz applies this to the world.

The ball in the woods

The philosopher Richard Taylor imagined finding a translucent ball in the woods. No one would accept the answer that it has no explanation. Defenders of the PSR say the case shows a deep rational habit, and critics say it shows only a habit.

Quantum events

On some interpretations, a radioactive atom decays at a time with no determining cause. If this is right, some events lack a sufficient reason. Defenders reply that these interpretations are disputed and that other interpretations restore causes. Critics say that physics should not be forced to fit the PSR.

Different perspectives

Catholic

Catholic philosophers who follow Aquinas hold a version of the argument from contingency, as in the Third Way. Some are cautious about the strong PSR as Leibniz stated it, preferring Aquinas’s more limited principle that being needs a cause. The Church has not taught on the PSR as such.

Orthodox

Orthodox thinkers affirm that the world depends wholly on God, and some, like Hart, defend arguments from contingency. Others are wary of any argument that makes God the answer to a philosophical need, preferring to say that God is known beyond all explanation.

Protestant

Leibniz was a Lutheran, and his Theodicy of 1710 was a major work of Protestant philosophy. Modern Protestant defenders of contingency arguments include Pruss and Koons. Many Protestants, following Barth or Plantinga, do not rely on this style of argument.

Scholarly views

Scholars of Leibniz disagree about how he understood contingency, since his view that God chooses the best world seems to make the world necessary. This is a long-standing puzzle in Leibniz studies.

Skeptical views

Many philosophers, including Bertrand Russell in a famous radio debate with Frederick Copleston in 1948, said that the universe is just there, and that the demand for an explanation of the whole is not required. This is the view known as the brute fact reply.

Why it matters

The argument from contingency is the heart of modern defenses of the cosmological argument, and the PSR is the most important single premise to understand. It shows how an argument can stand or fall on a principle that most people accept in daily life and few have examined.

Common misunderstandings

Misunderstanding: The PSR is a law of physics.

Correction: It is a philosophical principle about explanation. Whether it is true is a matter for argument and cannot be tested in a laboratory.

Misunderstanding: The argument says the world needs a first cause in time.

Correction: It does not. It works even if the world has no beginning, because it asks why there is a world at all.

Misunderstanding: Leibniz proved God’s existence beyond doubt.

Correction: He believed so. Most philosophers now consider his argument dependent on a premise that is disputed.

Misunderstanding: Anyone who rejects the PSR cannot do science.

Correction: Science needs to look for explanations. It does not strictly need the assurance that every fact has one.

Knowledge check

State the principle of sufficient reason.

It is the claim that every fact or truth has an explanation of why it is so and not otherwise. A weaker form says only that every contingent fact has an explanation. Leibniz held the strong form. Cosmological arguments from contingency need at least the weaker form to reach their conclusion.

How does Leibniz argue that an infinite series of contingent things would not be enough?

He says each member could be explained by an earlier one, but the question remains why there is any such series at all. No member can answer that question, because each is part of what needs explaining. So the explanation must lie outside the series, in a necessary being that is the reason for the whole.

What is the brute fact reply?

It is the claim that the universe, or some basic fact about it, simply exists with no explanation. This denies the PSR for the whole. Russell said in 1948 that the universe is just there. Defenders of the argument say that this gives up on explaining something that has an obvious claim to be explained.

What is the modal collapse objection?

Van Inwagen argued that if every truth has an explanation, and the explanation of the world’s existence is a necessary being, then it seems the world could not have been otherwise. This would make every fact necessary. Defenders propose ways a necessary being can freely choose among contingent outcomes, but the objection remains a central difficulty.

Think it through

  1. Which would you find more troubling: a universe with no explanation, or an explanation that makes everything necessary?
  2. Does the demand for explanation come from reason, or from habit?
  3. What kind of explanation could be sufficient for the whole of reality?
  4. How does your own life use the idea that things have reasons?

Independent assignment

Leibniz in numbered steps

In your own notebook, write 350 to 500 words. Write Leibniz’s argument from contingency as numbered premises. Next to it write the brute fact reply as a short argument. Then write a paragraph on which side seems stronger, and what extra evidence would change your mind. Do not send this to anyone.

Further study