Proving the existence of God is the primary and foremost step of proving Christianity. Without God, Christianity (or any deitized religion, for that matter) cannot possibly exist. Therefore, without God, Christians would not be Christians. It is obvious that one who does not believe in God cannot be a Christian. Thomas Aquinas, the great Catholic theologian of the middle ages, came up with 5 postulates to prove the existence of God. These postulates are extremely well written and used world-wide for Christian apologetics. They are summed up here.

Aquinas' First Argument, Motion
(1) Objects are in motion.
(2) If something is in motion, then it must be caused to be in motion by something outside of itself.
(3) There can be no infinite chain of movers/movees.
(4) So there is a first, unmoved mover.
(5) Therefore, God exists.

There are two main objections to this argument made by non-Christians. Both objections lead to one point. Some will object to step #2, saying that if that is the case, God too must have been set in motion by something else. However, these people miss the entire basis of the motion argument. The basis for this argument is that God is unmoved, and set everything else in motion. Therefore, because God is unmoved, He would not have to have been set in motion in the first place. And so these people will immediately side with the rest, now using the argument that there CAN be an infinite chain of movers/movees, which vilotes and thereby "disproves" step #3 of this argument. However, this "eternal chain of movers" objection opposes science and nature itself. A staff is moved only as much as the hand allows it to. Everything that moves has its movement determined by its mover, and all movement is from the original mover. Therefore, to use this objection would be to proclaim that there is no first mover (all movement is eternal) and consequently, there can be no other movers. The staff moves only because the hand allows it to. The hand moves only because the body allows it it, and so forth. To refuse the existence of a first mover is to refuse the existence of every movement thereafter. Therefore, there must be one original, unmoved mover, and that mover is commonly referred to as God.

Aquinas' Second Argument, Causality
(1) Some events cause other events.
(2) If an event happens, then it must be caused by something outside of itself.
(3) There can be no infinite cause/effect chains.
(4) So, there is a first, uncaused cause.
(5) Therefore God exists.

The only objection that can be made here is, again, that there CAN indeed be an infinite number of cause/effect chains. Aquinas recognized this objection, and refuted it in the following way: "Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false." Therefore, it is necessary to accept the existence of an uncaused cause, which is God.

Aquinas' Third Argument, Contingency
(1) Contingent things exist.
(2) Each contingent thing has a time at which it fails to exist (contingent things are not omnipresent).
(3) So, if everything were contingent, there would be a time at which nothing exists (call this an empty time).
(4) That empty time would have been in the past.
(5) If the world were empty at one time, it would be empty forever after (a conservation principle).
(6) So, if everything were contingent, nothing would exist now.
(7) But clearly, the world is not empty (premise 1).
(8) So there exists a being who is not contingent.
(9) Hence, God exists.

This argument is among the best. Little worthy objection arises from the study of this argument, save one. The only objection to this argument worth considering is that to step #4. And this objection is poor as well. Some will argue that there is no reason why the empty time would have had to have happened in the past. But by pure logic, it MUST have occurred in the past. Nothing can create itself. Therefore, all things must have been created or caused in some way (Deity Creation, evolution, etc.). Because things exist now, we know that these things must have been caused or created, and thereby we know that the time before that creation (empty time) must have happened in the past, because they currently exist. And so we can conclude that unless these things were non-contingent (omnipresent and eternal), they should never have existed unless empty time did already exist. Hence, empty time must have existed. And the Creator, non-contigent being we must accept to be God.

Aquinas' Fourth Argument, Properties That Come in Degrees
(1) Objects have properties to greater or lesser extents.
(2) If an object has a property to a lesser extent, then there exists some other object that has the property to the maximum possible degree.
(3) So there is an entity that has all properties to the maximum possible degree.
(4) Hence God exists.

Although this argument does very little to prove the glory of God, it does much to prove the existnece of God. Basically, the argument proves beyond reasonable doubt that something exists which in every way superior to any one of us. However, the argument does nothing to prove that God is divine nor Spiritual. This argument merely proves the validity of the definition and concurrent existence of God. But the argument leaves room for this God to be human or even animal. The argument also leaves open the possibility that God can vary from age to age.

Aquinas' Fifth Argument, From Design
(1) Among objects that act for an end, some have minds, whereas others do not.
(2) An object that acts for an end, but does not itself have a mind, must have been created by a being that has a mind.
(3) So there exists a being with a mind who designed all mindless objects that act for an end.
(4) Hence, God exists.

At first, this argument may seem rather weak. Humans are minded objects, and have the ability to create mindless things for a purpose. How does this prove the existence of God? Think in larger terms. Humans have the ability to create. Did they create the planet Earth? The sun? The entire, gargantuan universe? No. They are unable to. Just as a human has the ability to create a mindles object such as a watch for a purpose, so someone must have the ability to create such amazing things as the universe, a mindless object, for a purpose. That person, the maker of the un-human mindless objects, is God. One must simply glance around to see the wonders of the world. The huge, endless ocean, teeming with life. The millions of stars all shining bright. The closest star, the sun, giving life through its rays of light. The forests and jungles, filled with all kinds of interesting life. The squid, who shoots out ink in defense. The armored armadillo. The shark in its treacherous hunt. The lion in its majestic beauty. And the fact that all living creatures are dependant upon eachother and upon the Earth to survive. The Universe is truly amazing, and it is a miracle. One that could only have been created by a higher mind. That of God.

Anselm's Argument, Ontological
(1) God is defined as that which nothing greater can exist.
(2) It is greater to exist then not to exist.
(3) Therefore, God, being the greatest, must exist.

This argument is a peculiar one. It has intrigued many, and sparked the interests of others. Like Aquinas' fourth argument, this argument shows the existence of God without a doubt. It fails to, however, show the glory, power, or divinity of God. It merely proves that God exists. The Stanford Encyclopedia of Philosphy clarifies the argument like this:

The first, and best-known, ontological argument was proposed by St. Anselm of Canterbury in the 11th. century A.D. In his Proslogion, St. Anselm claims to derive the existence of God from the concept of a being than which no greater can be conceived. St. Anselm reasoned that, if such a being fails to exist, then a greater being -- namely, a being than which no greater can be conceived, and which exists -- can be conceived. But this would be absurd: nothing can be greater than a being than which no greater can be conceived. So a being than which no greater can be conceived -- i.e. God -- exists.

And so the existence of God, a Creator, higher thinker, or supreme being, is unmistakeable and obvious. And so we continue in our efforts to prove and portray the validity of Christianity and the Hard Evidence behind it.