'The Five Ways' | Aquinas's Proofs for the Existence of God | Summa Theologica I, q. 2, a. 3

What are Aquinas's Five Ways? What's the difference between an ontological and a cosmological argument? How does Aquinas answer the problem of evil?

[Leitmotif]

The first way 15:25
The second way 38:49
The third way 45:46
The fourth way 56:53
The fifth way 1:04:35

[arnoutis]

Very cool! Can't wait to see more content. Love the work. Becoming one of my favorite channels!

[zanecupp]

These videos are remarkable! Do you have plans to do any more in the future?

[TaeyunHan-xi]

Can you prove that whatever is unmoved mover is omnipotent, omniscient, omnibenevolent, unique, simple, and perfect?

[cf]

I thought “Whatever is in motion was put in motion by another” was actually “whatever is in motion is in motion by another” which I then couldn’t reconcile with Newton’s laws. Like I thought the agent had to be present and currently acting for motion to be according to Aristotle’s physics. Was I reading a bad translation or missing something? This may not be the place for such a technical question. Thanks for the talk anyways good stuff

[Enigmatic_philosopher]

Here is an attempt to symbolize some of the key problems with each of Aquinas' Five Ways using symbolic logic:

First Way (Motion)

1. Everything that is moved is moved by another (premise)
1. There cannot be an infinite regress of movers (premise)
1. ∴ There must be an unmoved mover (from 1 and 2)

Problem:
4\. ◇∃x(~Mx & ~∃yMyx) It is possible that there exists some x that is unmoved and yet there is no y that moves x

In other words, premise 2 is questionable because it is possible for there to be an infinite regress of moved movers, without any unmoved mover.

Second Way (Causation)

1. Everything that is caused is caused by another (premise)
1. There cannot be an infinite regress of causes (premise)
1. ∴ There must be an uncaused cause (from 1 and 2)

Problem:

4. ◇∃x(~Cx & ~∃yCxy) It is possible that there exists some x that is uncaused and yet there is no y that causes x

As with the First Way, premise 2 is doubtful because an infinite causal regress is possible.

Third Way (Contingency)

1. Contingent beings exist (premise)
1. Contingent beings require a necessary being (premise)
1. ∴ A necessary being exists (from 1 and 2)

Problem:

4. ~□∃xNx It is not necessary that a necessary being exists

The move from contingent beings to a necessary being is invalid. The existence of contingency does not necessitate the existence of necessity.

Fourth Way (Gradation)

1. Finite goods exist (premise)
1. Finite goods require a maximum good (premise)
1. ∴ An absolute maximum good exists (from 1 and 2)

Problem:

4. ~□∃x(Mx & ∀y(My → x≥y)) It is not necessary that there exists some x that is maximally good such that x is greater than or equal to any other good y.

An infinite regress of greater and greater finite goods is possible, without any absolute maximum good.

Fifth Way (Teleology)

1. Non-intelligent things act towards ends (premise)
1. Non-intelligent things require an intelligent director (premise)
1. ∴ There exists an intelligent director of things (from 1 and 2)

Problem:

4. ~□∃xDx It is not necessary that there exists some intelligent director x of things.

The move from the apparent functionality of nature to a cosmic intelligent designer is invalid, since there may be naturalistic explanations for biological teleology.

[apricus]

Is the word "exist" proper? What does "Ex" here mean. And what does "ists" like "status" or "state". Wouldn't this expression mislead? I mean there are young adults who argue against notion of God by speaking about "teacups" and "speghetti monster"? God is "in" and the sound "ex" impresses the mind the notion of being "out". So I heard someone "when scientists finally find God then I'll believe".

[Enigmatic_philosopher]

Here is a comprehensive philosophical critique of the arguments for God's existence in Summa Theologica:

First Way (Motion)

- The argument relies on an outdated Aristotelian physics that viewed motion as a transition from potentiality to actuality. Modern physics rejects this framework. Motion can occur without external causes.

- Even if we grant the principle that whatever is moved is moved by another, it does not logically follow that there must be an unmoved mover. There could be an infinite regress of moved movers, each moved by a prior cause. Aquinas gives no justification for rejecting such a series.

- The argument illicitly moves from observable motions to an unobservable first mover. We have no empirical evidence of a first uncaused cause of motion. It is a metaphysical assumption.

- The argument assumes that the first mover must be God. But even if we grant an unmoved mover, it need not have all the properties of God such as perfection, goodness, infinity etc.

Second Way (Causation)

- As with the first way, the argument relies on an outdated Aristotelian view of causation that is no longer accepted in modern science. Causes do not have to temporally precede effects.

- There are credible modern cosmological theories, like eternal inflation, that posit infinite causal regresses. Aquinas gives no good reason to reject such theories out of hand.

- The argument illicitly moves from observable chains of causation to an unobservable first cause. We have no empirical evidence of a first uncaused cause. It is a metaphysical assumption.

- Even granting a first cause, it need not have the properties of God. It could simply be an impersonal necessary being.

Third Way (Contingency)

- The argument relies on an Aristotelian cosmology of necessity and contingency that does not match our modern understanding of the universe.

- The argument illicitly moves from the existence of contingent beings to a necessary being. We have no empirical evidence of any non-contingent entities. It is a metaphysical assumption.

- The argument equivocates between ontological necessity and causal necessity. Something may be necessary causally but still contingent ontologically.

- Even granting a necessary being, it need not be God. It could simply be an impersonal ground of being.

Fourth Way (Gradation)

- The argument relies on an Aristotelian metaphysics of degrees of perfection that is questionable. There are other explanations for degrees besides exemplar causality.

- The move from finite goods to an infinite good is invalid. Infinite regresses are possible, so no maximum is necessarily implied.

- The maximum being inferred need not be God. It could simply be an impersonal absolute. The properties of goodness, knowledge, power are assumed rather than proven.

Fifth Way (Teleology)

- The argument relies on empirically questionable teleological explanations in biology. Most adaptation is explained by natural selection, not intentional design.

- Even granting the analogy of design, at most this proves a designer, not necessarily God. We have no warrant to assign properties like perfection, infinity or creativity to the designer.

- The argument illicitly moves from particular cases of apparent design in nature to a cosmic designer. Local adaptation does not imply cosmic teleology.

In summary, Aquinas' five ways are based on Aristotelian metaphysics, science and logic that is outdated and empirically dubious. They rely on illicit moves from the observable world to unobservable metaphysical assumptions. And even granting their dubious premises, they do not lead specifically to the God of classical theism. At best, they point to an impersonal first cause, necessary being, maximum goodness or intelligent designer. Aquinas' arguments are ingenious products of their time, but they do not provide compelling reasons to believe in God from the perspective of modern philosophy and science.