Philosophical Arguments for God’s Existence

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Philosophical Arguments for God’s Existence

  • Prof. Rob Koons
  • (Unpublished Papers)
  • Leadership for America 2013

Can we “prove” that God exists?

  • Much depends on what we mean by “prove”.
  • We can’t prove God’s existence in the way that one can “prove” a theorem of mathematics, like the Pythagorean theorem or the existence of infinitely many prime numbers – by pure logic from axioms everyone accepts.

God and Natural Reason

  • However, we can know by natural reason (and not only by faith) that there is a God. This knowledge is available to anyone with fully functioning rational faculties. However, these faculties can be damaged by sin (both individual and societal).
  • To know God’s existence, we must be willing to follow reason to its utmost limit.

Doubt can be Healthy or Unhealthy

  • A healthy doubt enables us to think more clearly and responsibly, by protecting us from irrational fads, myths and fables.
  • A healthy doubt promotes a prudent humility and openness to new information.
  • However, doubt, when carried to extremes, actually paralyzes thought, making us doubt those first principles without which all knowledge would be impossible.

The Error of the “Enlightenment”

  • The “Enlightenment”, beginning with the French philosopher and mathematician René Descartes (1596-1650) and the British philosopher John Locke (1632-1704), created the Myth of the Method.
  • According to this Myth, all human reasoning can be reduced to a mechanical recipe, a set of procedures that all can follow to reach the right conclusions, without the need of exercising judgment or wisdom.

Post-Modernism: The Overreaction

  • The Enlightenment idea experienced a series of catastrophic refutations in the 19th and 20th centuries, as philosophical rationalism failed to produce the universal consensus that the Enlightenment had promised.
  • In modern times, post-modernism has arisen as a natural reaction to this failure: denying the very existence of human reason or of a universal Truth (with a capital T), as opposed to “my truth” or “our truth”.

The Post-Modern Mindset

  • Post-modernists are suspicious of any claim to have or to know any universal truth.
  • They tend to see the use of logic, argumentation, or reasoning as a form of coercion or aggression.
  • “Tolerance” becomes the only virtue.

Post-Modernists are Inconsistent

  • However, no one can really live as Post-Modernists claim.
  • Post-Modernists believe that they do possess a universal truth: the truth that there is no universal truth.
  • Post-Modernists are intolerant of those who do not practice post-modern ‘tolerance’.

So, What to do?

  • Realize that the Post-Modernists are wrong about everything, including post-modernists.
  • All human beings have a natural aptitude for Truth, and the human mind has a fundamentally rational structure that cannot be erased.

Proving God’s Existence

  • What follows will be based on Ways 1-3 of St. Thomas Aquinas’s Summa Theologica I 2 a3, and his much longer Summa Contra Gentiles:
  • By Alexander Pruss, at Baylor: The Principle of Sufficient Reason (Cambridge Univ. Press, 2010).
  • Also, some of my own work, including my chapter in Oxford Studies in the Philosophy of Religion, vol. 1, ed. Jonathan Kvanvig, 2008, and “A New Kalam Argument”, Noûs 2012 (forthcoming).

An Argument with a Long History

  • Accepted by philosophers from six great traditions:
    • Ancient pagan (Greek and Roman)
    • Jewish
    • Christian
    • Moslem
    • Indian (10th century Nyaya school)
    • Early modern European
  • Developed over 2500 years.

Endorsed by many philosophers

  • Plato and Aristotle, Plotinus
  • Maimonides, al-Farabi, Avicenna, Averroes, Udayana
  • St. Thomas Aquinas, John Duns Scotus
  • Rene Descartes, Gottfried Leibniz, John Locke.
  • Frederick Copleston, Mortimer Adler, Etienne Gilson, Richard Taylor, Austin Farrer, Richard Swinburne, Timothy O’Connor, Alexander Pruss

What do we know?

  • Hold out your right hand, and spread out your fingers.
  • Do you know that there is a hand with five fingers in front of you?
  • If so, you can also know that God exists

Empirical Knowledge

  • Your knowledge of your hand and its fingers is a case of ‘empirical knowledge’:
    • Things we know by observation (using the five senses)
    • Things we know by memory (remembering what we have observed)
    • Things we know by the testimony of others
    • Things we can infer from these by scientific or historical reasoning

Empirical Knowledge Depends on “Causality” (Cause and Effect)

  • When we know something empirically, our belief is linked by a chain of cause and effect to the thing we know.
    • Sensory perception involves a chain of cause and effect (e.g., light reflection, retinal stimulation)
    • Memory involves a chain of causes in the brain, recording and recalling a memory trace
    • Testimony is passed down a chain of communication events
    • Scientific and historical reasoning infers causes from effects or effects from causes.
  • Causal Chain
  • If any of these steps could occur without a cause, knowledge would be impossible.

Does everything have a cause?

  • Everything involved in empirical knowledge must have a cause.
  • Suppose, for example, that sensations could occur without any cause whatsoever.
  • If that were ever possible, it would be possible all the time, and with a completely unpredictable and inscrutable probability.
  • We would have good reason to think that we might be “Boltzmann brains” right now – with nothing but illusory sensations.

Universal Causality must be Self-Evident

  • We supposed that we did have some empirical knowledge (remember the five fingers).
  • But such knowledge is impossible unless we know that every step involved (before the last one) necessarily has a cause.
  • We can’t know that empirically (without vicious circularity), so it must be a self-evident principle of reason. To doubt this is the unhealthy kind of doubt.

Evidentially Proximate vs. Ultimate

  • There is one sort of thing that could fail to be caused, without threatening empirical knowledge: “ultimate” things.
  • Something is “ultimate” just in case it is obviously and certainly the kind of thing that could not possibly be evidence for anything else.
  • Not just uncaused but self-evidently uncausable.

The Universal Causation Principle

  • Let’s say that something is ‘natural’ just in case it isn’t ultimate.
  • Reason tells us, with certainty:
  • Every natural thing must have a cause.

Does Absolutely Everything have a Cause?

  • If absolutely everything had a cause, then the network of causation would have to contain either (i) loops (things that caused themselves) or (ii) infinite regresses.
  • However, nothing can cause itself, since it would have to both exist (in order to be the cause) and not exist (in order to be a potential effect) at the same time.

The Grim Reaper Jose Benardete’s Infinity: An Essay in Metaphysics (1964)

  • Death to Fred!
  • 12:01
  • 12:00:30
  • 12:00:15
  • 12:00:07.5
  • 12:00:03.75
  • 12:00:01.875
  • Death to Fred!
  • Death to Fred!

The Unbounded Version

  • 1 B.C.: GR #1
  • 2 B.C: GR #2
  • 3 B.C.: GR #3
  • etc.
  • Each Grim Reaper issues a death warrant for Fred if and only if no preceding GR has done so.
  • (Invented by Prof. Pruss at Baylor, 2009.)

Story leads to a Contradiction

  • At least one GR has initiated a death warrant, since otherwise all would have failed to do their duty. Say it was GR #n
  • GR #n would have acted only if all earlier GR’s did not act. So, both GR #(n+1) and GR#(n+2) did not act.
  • But, if GR#(n+2) and all earlier GRs did not act, then GR#(n+1) would have acted. Contradiction.

Reductio ad Absurdum

  • If a contradiction follows logically from a proposition, then that proposition must be false.
  • The GR story follows from the proposition that an infinite regress is possible, and the GR story is self-contradictory.
  • Therefore, an infinite causal regress must be impossible.

Another argument for a First Cause

  • Even if infinite regresses were possible, they would have to have a cause as well. The Gale-Pruss cannonball argument.
  • Let the Cosmos = the sum of all variable, contingent facts. The Cosmos will itself be contingent, so it comes under the Universal Causal Principle.
  • The cause of the Cosmos must be separate from it – and so must be infinite and necessary. (This argument is from al-Farabi, Duns Scotus, and Gottfried Leibniz)

Existence of a First Cause

  • If the network of causation contains no loops and no infinite regresses, then there must exist at least one uncaused or “First” cause.
  • However, we have seen that empirical knowledge requires that every natural thing must be caused.
  • So, any First Cause must be “ultimate”: obviously (self-evidently) incapable of being evidence for anything else, i.e., uncausable.

What must Ultimate things be like?

  • What characterizes all the natural things? (Things we perceive or remember, things that are intermediate between perceptions and objects, things that can be used as scientific data)
  • They are all (obviously) variable, inconstant, changing.
  • So, an ultimate thing (a First Cause) must be invariant, constant, unchangeable.

Nature of the First Cause

From First Cause to Absolute Being

  • In order to be uncaused, the First Cause must be necessary (constant and invariant).
  • In order to be necessary, the FC must be infinite in every respect, because what is finite is variable.
  • In order to be necessary in itself, the FC must be simple or absolute Existence, since if it were not, it would be limited or bounded in some way, and so finite.

From Absolute Being to One God

  • There could be only one thing that is identical to Absolute Existence, because if there were two, they’d be identical to each other.
  • This being must have all possible power, since it must be the cause of all possible beings.
  • In order to have all possible power, it would have to possess all positive attributes to their absolute maximum degree: perfect knowledge, beauty, wisdom, goodness, etc.

To Summarize

  • If uncaused, then ultimate.
  • If ultimate, then self-evidently uncausable (“SU”).
  • If SU, then unbounded, unconstrained and unlimited in every respect (“UUU”).
  • If UUU, then identical to pure existence (“IPE”).
  • IF IPE, then one and perfect.
  • If one and perfect, then God.

Some Limitations of the Argument

  • We know that the First Cause is infinite and has every purely positive ‘perfection’.
  • We know a lot of negative things about the FC: immaterial, timeless, unbounded.
  • However, the argument doesn’t show that the FC is personal (wise, knowledgeable, just, loving) – since it isn’t obvious that those qualities are purely positive.
  • Even if God were perfectly powerful and knowledgeable, it wouldn’t follow that He was omnipotent or omniscient (capable of doing and knowing absolutely everything).

The One-Two Punch

  • To summarize this lecture and the two arguments on design (fine-tuning and biology), we have a convergence of arguments for the conclusion that the universe has a supernatural cause:
    • From physics – the Big Bang and fine tuning.
    • From metaphysics – the First Cause arguments.
  • The two together are much stronger than either separately. Physics makes God’s existence probable, metaphysics makes it certain.

William Paley’s Design Argument (By Analogy)

St. Thomas’s Cosmological Design Argument (5th Way)

Advantages of the Latter

  • Avoids the infinite regress objection of skeptics like Dawkins: “Who made God?”
  • Starts with a cause of the Cosmos: uses design only to establish and confirm God’s intelligence.
  • Supplies crucial facts about God: eternal, immaterial, infinite, wholly good

Answering some objections

  • Necessary existence is impossible.
  • Quantum Mechanics teaches that some events are uncaused
    • No -- it teaches that some events are caused but not pre-determined in every respect.

Hume’s Objection

  • God cannot exist necessarily.
  • What we can imagine existing, we can imagine not existing.
  • What we can imagine is possible.
  • So, if God’s existence is possible, so is His non-existence.


  • Not everything we can imagine is really possible (time travel, infinite regresses).
  • We cannot imagine God’s existing or not existing: God’s being is beyond our comprehension. However, we can know that He exists (by the First Cause argument).

Kant’s objection

  • The first cause argument supposes that God’s existence is necessary.
  • To be absolutely necessary, God would have to exist by definition.
  • However, nothing can exist by definition. Suppose, for example, that I defined a ‘schmountain’ as a golden mountain that exists.
  • We cannot conclude that schmountains exist by definition, since that would entail that gold mountains exist.


  • We are not saying that God exists by definition – just that He is uncausable by definition. Golden mountains are not uncausable. We conclude that God exists by argument, not by definition.
  • If such a God exists, He exists by virtue of His own nature. Only an infinite and simple being could exist in this way.

Why believe the principle of causality?

  • Perhaps it [the principle of causality] just expresses an arbitrary demand; it may be intellectually satisfying to believe that there is, objectively, an explanation for everything together, even if we can only guess what the explanation might be. But we have no right to assume that the universe will comply with our intellectual preferences.
  • J. L. Mackie, The Miracle of Theism: Arguments for and against the Existence of God (Clarendon Press, Oxford, 1982), p. 86.

Is the Argument Self-Contradictory?

  • ...the causal argument is not merely valid but self-contradictory: the conclusion, which says that something (God) does not have a cause, contradicts the premise, which says that everything does have a cause.
  • John Hospers, An Introduction to Philosophical Analysis, 2nd edition (Prentice-Hall, Englewood Cliffs, NJ, 1967), p. 431.

Objection: Why Can’t Matter be Ultimate?

  • Aquinas’s implicit assumption is that anything whose essence does not involve existence must, even if it is permanent, depend for its existence on something else... we have no reason for accepting this implicit assumption. Why, for example, might not there be a permanent stock of matter whose essence did not involve existence but which did not derive its existence from anything else?
  • J. L. Mackie, The Miracle of Theism: Arguments for and Against the Existence of God (Clarendon Press, Oxford, 1982), p. 91.

Couldn’t the Universe itself be a First Cause?

  • No – the universe is merely an aggregate of things, each of which is variable and contingent.
  • What about the Big Bang?
  • We know that it is finite in many dimensions (the fine-tuned constants, entropy, velocity).
  • It isn’t ultimate: it isn’t obviously uncausable. God is – by definition.

Objection: Why stop with God?

  • All three of these arguments (Aquinas’s first three ways) rely upon the idea of a regress and invoke God to terminate it. They make the entirely unwarranted assumption that God himself is immune to the regress. Even if we allow the dubious luxury of arbitrarily conjuring up a terminator to an infinite regress and giving it a name, simply because we need one, there is absolutely no reason to endow that terminator with any of the properties normally ascribed to God: omnipotence, omniscience, goodness, creativity of design... Richard Dawkins, The God Delusion, Houghton Mifflin, Boston, 2006, p. 77
  • But the greatest weakness of this otherwise attractive argument is that some reason is required for making God the one exception to the supposed need for something else to depend on: why should God, rather than anything else, be taken as the only satisfactory termination of the regress? If we do not simply accept this as sheer mystery..., we shall have to defend it in something like the ways that the metaphysicians have suggested. J. L. Mackie, The Miracle of Theism: Arguments for and Against the Existence of God, 1982, p. 92.

Can God be Ultimate (Self-Explanatory)?

  • It is utterly impossible for God to be self-explanatory, Theists usually consider God's existence to be part of His essence and maintain that this renders God self-explanatory. But what do we mean by a certain characteristic’s being part of the essence of a thing? The essence of a thing is what it is. The essence of a table, for example, is whatever is common to all particular instances of tables. Having a flat surface on top is a characteristic which is part of the essence of a table. But the fact that anything that is a table must have a flat surface does not explain why this particular thing was constructed as a table -- that is, why it is a table. It merely explains why the thing must have a flat surface if it is a table. Similarly the fact that God has an essence which includes existence would not explain why God is a being which has this particular essence. It only explains why he must exist if he has the particular essence he happens to have.
  • B. C. Johnson, The Atheist Debater’s Handbook (Prometheus Books, NY, 1983), p. 66.

Is God utterly Unknowable?

  • Despite the complicated maneuvers of Christian theologians to escape from agnosticism, despite the abstract dissertations and impressive sounding attributes of God, it always comes down to this: the nature of God is “entirely unknown” to man. The characteristic under consideration -- the identity of God's essence and existence -- is nothing more than an extremely complicated way of conceding the very point which we are attempting to prove: that the very concept of God is without cognitive content. The Christian cannot give substance and meaning to the term “God”; it is a blank, an unknown “something”.
  • George H. Smith, Atheism: The Case Against God (Prometheus Press, NY, 1989), p. 66.

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