1. Philosophy and the proof of God's existence
Is Religion Reasonable? Faith Seeking Understanding

2. Philosophy and the proof of God's existence
There are many traditional "proofs" for the existence of God, and we will look at three of them:
The ontological argument
The cosmological argument
The teleological argument (from design)

3. Even the person who denies that God exists claims to know what it means to say that God does not exist. That is, in denying that God exists, even the atheist acknowledges that by "God" is meant the supreme being; it's only that, as far as the atheist is concerned, such a supreme being does not exist.
Instead of calling God the supreme being, St. Anselm of Canterbury ( ) says that even an atheist, therefore, would agree that by "God" people mean that being than which nothing greater can be conceived.

4. Anselm then adds a second observation: wouldn't a being that exists both in reality and as a concept in people's minds be greater than that existed only in people's minds? For example, wouldn't a winged horse that really existed be a greater being than one that existed only in people's minds? That is, it seems that something that exists both outside the mind (extra-mentally) plus in the mind is greater than something that exists only in the mind. An idea of having $100 is certainly not as great as both having the idea and actually having the $100. Furthermore, a being that must exist (that is, one that exists necessarily ) is greater than one that exists contingently (that is, depending on another for its existence).

5. The Ontological Argument
St. Anselm ( )
P1: “God” means the greatest conceivable being
P2a: A being that exists in one’s mind and in reality (outside of one’s mind) is greater than one that exists only in one’s mind
P2b: A necessarily existing being is greater than a merely possible being
Therefore, God must exist in reality

6. The ontological argument
God is the perfect being. As He is most perfect, He must have all perfections. If God lacked existence He would not be perfect, as He is perfect he must exist.

7. So if God is that being than which nothing greater can be conceived, then God cannot be some being who exists only mentally (as someone's idea), because there would be a being who is greater--namely, one who exists extra-mentally and mentally.

8. So the only appropriate way to think of God is as a being who exists necessarily, both mentally and extra-mentally. And if God's existence (by definition) means that he exists not only in people's minds but also outside people's minds, then God must exist outside people's minds: that is, God exists necessarily.

9. The ontological argument
In summary:
1. Everyone acknowledges that by "God" we mean that being than which nothing greater can be conceived.
2. But a being that exists only in the mind is not as great as a being that exists in the mind as well as in reality. Real existence + conceptual existence > conceptual existence alone.
3. Therefore, God must exist both in the mind and in reality, since a God who existed only in the mind would not be that being than which nothing greater could be conceived. Since God is always on the left of the greater-than sign, God must really exist.

10. Notice this about the argument: it does not start from our experience of the universe; it starts simply from the meaning of the notion of God . If you know what the concept God means, you must conclude that God exists. If you don't, you don't know what you are talking about in talking about God.

11. Objections to Anselm’s Argument
Gaunilo: imagining anything as perfect does not make it exist. Reply: the non-existence of everything other than God is conceivable
Aquinas: if there is a greatest conceivable being, he exists; but we cannot simply assume his existence based on our meaning of “God.” Reply: what else could we mean?
Kant: A concept of God + a concept of his existing may be greater than a concept of God alone; but these are only concepts, not claims about existence outside our concepts. Reply: why can’t we discuss such external existence?

12. The cosmological argument (God as "First cause")
Everything that exists has a cause. However, there must at some time have been a cause prior to all other causes. This 'prime mover' or first cause is necessary to explain existence. This first cause is God.

13. The Cosmological Argument: St. Thomas Aquinas (1225-74)
The universe, like all things in it, is contingent (i.e., depends on something else as the cause of its existence); otherwise, it is unintelligible
If there is no essential cause of the universe (that is, if the causal sequence is infinite), then nothing would be happening or be intelligible here and now. But things do exist here and now, so God exists here and now

14. Aquinas’ 5 proofs for God’s Existence
1 – MOTION/CHANGE
Resulted from Aquinas’ study of the cosmos
There must be an ultimate cause for the motion that exists in the universe. It is God.

15. 2 – CAUSE
There must be an uncaused cause that started the causal chain in the universe

16. 3 – CONTINGENCY
Things in nature can exist or cease to exist.
Something can start to exist only through the actions of things that already exist. e.g. Making babies, planting seeds.
There must be something which derives its existence from itself and not from something else - GOD

17. 4 – PERFECTION
The perfect values must exist in order for the “partial values” to resemble them.
We strive for perfection, the perfect ideal must exist in order for us to strive for-GOD

18. 5 – DESIGN
God is the supreme wise intelligence in whom all order in the universe originates.
The universe is perfect, ordered and purposeful, because God designed it to be so.

19. Hume’s Criticisms of the Cosmological Argument
No being (including God) exists necessarily
If God is eternal, why not the universe too?
Fallacy of composition: parts  whole
Why should we think that everything has a cause or reason for its existence?
Besides, the argument does not prove that God is anything other than a cause of things who might not care at all about his creation

20. Traditional "proofs" of God's Existence
The argument from Design
If you found a clock and examined the mechanism within it, you would probably think that this intricate mechanism was not the outcome of mere chance, that it had been designed.

21. The argument from Design
Now look at the universe; is it possible that such an intricate mechanism, from the orbits of planets round the sun to the cells in your fingernails could all have happened by chance? Surely, this enormously complex mechanism has been designed, and the being that designed it must be God.

22. The Teleological Argument: Argument from Design/Purpose
Wm. Paley
( )
(A posteriori vs. a priori argument)
The order and intricacy of things in the universe make sense only if an ordering and purposive mind is their cause
Analogy: watch universe
watchmaker universe-maker

23. Criticisms of the Teleological Argument: David Hume
Even the claim that the universe exhibits order is doubtful; it is a human imposition
We cannot use analogy in discussing the universe: we do not experience universes or know that intelligent beings produce them
Even if we argue analogously, we cannot conclude that its creator is one, wise, good or even still existing

24. Criticism of the Design Argument: Charles Darwin
( )
Things in nature exhibit order, but that is not the result of design or purpose
Things appear orderly because random variations produce adaptive individuals
Objection (Fine Tuning Argument): divine design is a more likely explanation for the intricate conditions needed for life