(Question 1 is a quick recap of nature of doctrine, read it here if you want)
Question 2 answers for the existence of God. That is, how do we know God exists? This is called his Five Ways (quinqae viae, Latin) since there are to him, five means of knowing God exists from “proof”. Keep in mind this is not the sort of “proof” that is offered in labs where material hypothesis are testable, because God is not a material thing, but instead is on the basis of philosophy and logic.
The first is motion. Where motion exists there must be a mover and ultimately there must be a first mover, unmoved. For example, all things are set in motion by another, but there cannot be, by that very rule, an infinite set of movers; there has to be a prime and first act of motion. This is God.
The second is efficient cause, where like motion, there are effects in the universe and each effect has a cause. Because we know no particular thing which caused itself, each cause in turn has its father cause and ultimately there must be a first cause which is uncaused. This is God.
Third is the concern of possibility or “contingency”. Things that are contingent do not have to exist (not necessary) but are only possible. Obviously, things in the universe do exist so there must have been a thing in the universe which was necessary and non-contingent. The contingent undergo change and thus are finally existent like the master bringing the sculpture out of the marble. The sculpture was possible but needed a change to come out of the material. That change is unnecessary, it ever needed to happen. Therefore anything that is unnecessary but is, we can deduce that a necessary thing brought it into being. This necessary being is God.
Fourth is the gradation, or the degrees of perfection in which things are observed. In things we find varying levels of good and better, more and less, etc., which are smaller levels of an utmost in their category. There are levels of beauty, levels of light, levels of love, and all intellects recognize this but ultimately there has to be a best or a perfect or an utmost. This utmost is God.
Finally, the fifth proof of God’s existence is the observation of governance in the world. Things in the world act in specific ways as if programmed (governed) like a computer and every computer has a program which requires intelligence; an intelligent programmer. This is God.
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