Arguments based on Motion & Causality



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Arguments for God’s Existence
Arguments based on Motion & Causality

St. Thomas Aquinas (1224 – 1274) argued that there must have been a first cause, an “unmoved mover” to begin all of the causal chains of events that go on around us. This First Cause could only be God. Therefore, God must exist.



Problems:

  • Misunderstanding of motion: If something remains in motion, Aquinas believed something outside of that object must be continuing to push it. But we now know that momentum can explain continued motion.

  • An initial cause would not have to have the “God-making” properties (omniscience, omnipotence, omnibenevolence). Also, an initial cause would not have to be in existence now.

  • Why not more than 1 initial cause?

  • Why not an infinite sequence of previous causes (no beginning)?

  • Why not uncaused events?


The Design Argument

Aquinas’s version:



  1. There exist many objects that act for an end or purpose.

  2. Some of these objects do not have minds, so they could not have decided on their own to act this way.

  3. Some being with a mind must have designed these mindless objects so that they act for an end or purpose.

  4. Therefore, God must exist (and is this designer/creator).

Act for an end = act so as to fulfill a purpose.

E.g., A guided missile adjusts its behavior to fulfill a purpose, but does not have a mind. It can do so only because beings with minds (people) designed it to do this.

Many objects (bacteria, trees, etc.) act for an end, but do not have minds. So, Aquinas says, they must have been designed.

William Paley (1743 – 1805) says that when one finds a sophisticated system or mechanism, one automatically assumes that it has a designer. (Watches, etc. don’t just come into existence by themselves or by accident.) The existence of sophisticated natural systems (eyes, ecosystems, etc.) indicates the existence of a designer. Only God can fill this description.

David Hume’s criticisms. In his Dialogues on Natural Religion, Hume challenges the design argument.


  • The analogy between watches (which clearly have designers) and the universe is weak. Paley is ignoring many dissimilarities.

    • This is probably not a major flaw – all Paley needs is the fact that both systems are complex and fulfill a function.

The Evolutionary Criticism: Paley was not aware of how powerful the evolutionary explanation is. It can account for the complexity and sophistication of natural biological systems without having to include God.

  • Evolution is generally considered to be consistent with most religious doctrines regarding the origins of the Earth and the life upon it. Thus, the theory of evolution should not be regarded as somehow anti-theist.

  • Creationism is sometimes offered as a present-day version of the design argument. This turns out not to be an effective line of argument.

    • Criticisms of evolutionary theory are generally uninformed and logically flawed.

    • Creationism does not qualify as a scientific theory because it does not generate testable hypotheses. Thus, it is not a suitable alternative within a scientific context.


The Ontological Argument

First presented by Anselm (1033 – 1109, Archbishop of Canterbury; argument presented in 1077).



  1. I can conceive of a perfect being, one with all the perfect-making properties. (This is what we mean by “God” – one with all the perfect-making properties.)

  2. Objects that exist in reality are more perfect than those that exist merely in the mind.

  3. Therefore, a being with all the perfect-making properties would have to exist in reality.

  4. Therefore, God exists.

Problem: This argument assumes that existence is a property (along with being brown, or being rectangular). This is an error; existence is not a property.
Reductio ad absurdum version of the ontological argument:

The argumentative strategy: A reductio ad absurdum argument shows that a particular assumption leads to a contradiction. (A contradiction is a situation in which a particular proposition is said to be both true and false. Contradictions are guaranteed to be false.) Any assumption that leads to a contradiction must be false, so we can conclude that its negation (roughly, its opposite) is true. Here’s the argument:



  1. A being is God only if is the greatest conceivable being. (This is taken to be part of the definition of “God.”)

  2. God exists in the mind, but not in reality. (This is the assumption made for the reductio ad absurdum strategy. This will lead to a contradiction, and the argument will conclude that its opposite is true. Something is said to exist in the mind if we can understand it.)

  3. Existence both in reality and in the mind is greater than existence in the mind alone.

  4. We can conceive of a being that is like God but that also exists in reality.

  5. Thus, we can conceive of a being that is greater than God.

  6. Thus, we can conceive of a being that is greater than the greatest conceivable being. (This is a contradiction, and it follows from the assumption made in premise 2.)

  7. Thus, premise 2 must be false.

  8. Thus, God exists in the reality as well as in the understanding.

Criticism of Anselm’s ontological argument: Gaunilo’s Perfect Island Objection

Shortly after Anselm presented his argument, a monk named Gaunilo presented a parallel argument intended to show that Anselm’s argument doesn’t work. Here’s Gaunilo’s argument:



  1. An island is the Isle of Perfection only if it is the greatest conceivable island.

  2. The Isle of Perfection exists only in the mind, and not in reality. (Assumed for the reductio ad absurdum strategy.)

  3. Existence both in reality and in the mind is greater than existence in the mind alone.

  4. We can conceive of an island that is like the Isle of Perfection but that also exists in reality.

  5. Thus, we can conceive of an island that is greater than the Isle of Perfection.

  6. Thus, we can conceive of an island that is greater than the greatest conceivable island. (This is a contradiction, and it follows from premise 2.)

  7. Thus, premise 2 must be false.

  8. Thus, the Isle of Perfection exists in the reality as well as in the understanding.

Gaunilo wants us to recognize that there is no Isle of Perfection, so there must be some flaw in this argument. And if there is a flaw in the Isle of Perfection argument, the same flaw must be found in the ontological argument for God as well (because they have exactly the same structure). Thus, the ontological argument is not convincing.
Arguments Against God’s Existence
The Logical Problem of Evil

This deductive argument is intended to show that the following propositions are logically inconsistent:

(G) God exists, and is omnipotent, omniscient, and omnibenevolent.

(E) There is evil.

If these are inconsistent, then one of them must be false. We have excellent evidence for the truth of (E), so (G) must be false. That is, either God does not exist, or God lacks one or more of the properties listed in (G).
Criticism: (G) and (E) are logically consistent. There are reasons why a God with the properties listed in (G) would permit evil. E.g., Some evil is the fault of humans, or is necessary for us to learn moral lessons, or some evil is required to bring about a much greater good.
The Evidential Problem of Evil

This argument is intended to show that God’s existence is incompatible with the existence of unjustified evil.



  1. If there is unjustified evil, then God does not exist.

  2. There is unjustified evil.

  3. Therefore, God does not exist.

Although critics can argued that some of the evil in the world is justified (e.g., because it brings about a greater good, or because humans are at fault for it, or because it is necessary for us to learn moral lessons), there remains excess or unjustified evil. A just, loving, all-knowing, and all-powerful God would not permit this much evil. Thus, the existence of all this evil indicates that God does not exist.

The evidential problem of evil can also be put this way:



  1. God would want to (and would be able to) create the best world possible.

  2. The best world possible would not have any excess or unjustified evil.

  3. Our world has excess or unjustified evil.

  4. Therefore, God does not exist.


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