By Peter Kreeft in Summa of the Summa
1.Ontological (Anselm): “God” means “that which has all conceivable perfections”; and it is more perfect to exist really than only mentally; therefore God exists really. The most perfect conceivable being cannot lack any conceivable perfection.
A. Motion: Since no thing (or series of things) can move (change) itself, there must be a first, unmoved mover, source of all motion.
B. Efficient causality: Nothing can cause its own existence. If there is no first, uncaused cause of the chain of causes and effects we see, these second causes could not exist. They do, so it must.
C. Contingency and Necessity: Contingent beings (beings able not to be) depend on a necessary Being (a being not able not to be).
D. Degrees of perfection: Real degrees of real perfections presuppose the existence of that perfection itself (the perfect Being).
E. Design: Design can be caused only by an intelligent designer. Mindless nature cannot design itself or come about by chance.
F. The Kalam (Time) Argument: Time must have a beginning, a first moment (creation) to give rise to all other moments. (The ‘Big Bang’ seems to confirm this: time had an absolute beginning 15 - 20 billion years ago.) And the act of creation presupposes a creator.
A. From mind and truth
1. Augustine: Our minds are in contact with eternal, objective and absolute truth superior to our minds ( e.g. 2 + 2 = 4 ) and the eternal is divine, not human.
2. Descartes: Our idea of a perfect being (God) could not have come from any imperfect source (cause), for the effect cannot be greater than the cause. Thus it must have come from God.
B. From will and good
1. Kant: Morality requires a perfect ideal, and requires that this ideal be actual and real, somewhere.
2. Newman: Conscience speaks with absolute authority, which could come only from God.
C. From emotions and desire.
1. C . S . Lewis: Innate desires correspond to real objects, and we have an innate desire (at least unconsciously) for God, and Heaven.
2. Von Balthasar: Beauty reveals God. There is Mozart, therefore there must be God.
D. From experience
1. Existential Argument: If there is no God (and no immortality) life is ultimately meaningless.
2. Mystical experience meets God.
3. Ordinary religious experience (prayer) meets God. Prayer of the Skeptic: "God, if you exist, show me" - a real experiment.
4. Love argument: If there is no God of love, no absolute that is love, then love is not absolute. Or, the eyes of love reveal the infinite value of the human person as the image of God.
4. The argument from the analogy of other minds, which are no harder to prove than God (Platinga).
5. The practical argument: Pascals wager: To bet on God is your only chance of winning eternal happiness, and to bet against Him is your only chance of losing. It is the most reasonable bet in life.
A. From miracles: If miracles exist, a supernatural miracle-worker exists.
B. From providence, perceivable in history (e.g., in scripture) and in ones own life.
C. From authority: Most good, wise, reliable people believe in God.
D. From saints: You see God through them. Where do they get their joy and power. As with Mother Teresa of Calcutta.
E. From Jesus: If God is unreal, Jesus was history’s biggest fool or fake.
The full discussion of 20 Arguments is found here.