I agree with those who remark that philosophy begins and ends with Plato. There really wasn't anything the Socratic dialogues didn't touch upon in at least some manner. With that said, a very simple, yet overlooked argument for God's existence is based solely on the uniformity we have in our general experiences. This proof actually precedes Plato, and goes at least as far back as some of the pre-Socratics.
To begin with, we observe through experience that the universe contains order. In popular parlance, we often refer to this as the "uniformity of nature." By "order," I'm referring to patterns of regularity that allow our experiences to be intelligible. We find innumerable examples of this throughout our observations. For instance, it is true at all times and in all places that "A=A" (the law of identity), "If A=B and B=C, then A=C" (the transitive axiom), and "2+2=4" (a simple mathematical proposition).
Now, if the universe is imbued with order, then it corresponds to some ordering principle. By analogy, we might say that a red barn corresponds to the principle of redness. Likewise, everything that has order corresponds to an ordering principle. Hence, we can see that this claim is true by definition.
We can summarize the argument so far as follows:
1. Everything that has order corresponds to an ordering principle.
2. The universe has order.
3. Therefore, the universe corresponds to an ordering principle.
Very few people will actually disagree with any of this. The most likely objection is that this proof commits the fallacy of composition. An example of this fallacy is if we were to say:
1'. Every part of the floor is small.
2'. Therefore, the entire floor must be small.
The reason this is fallacious is because what may apply to the parts does not necessarily apply to the whole. The entire floor may very well be large, even if it is composed of small pieces. This is called an incidental composition.
In response to this, we can note that the proof does not rely on an incidental composition, but rather an essential composition. If every part of the floor is made of wood, then the entire floor must be made of wood. The same is true with an ordered universe. If every part of the universe contains order, then it is inconceivable how the universe as a whole could somehow lack order.
Another objection is that chaos exists. However, this objection doesn't work either for the simple reason that the reality of chaos does not do away with the reality of order. Moreover, chaotic events are still intelligible - that is, we are capable of having knowledge of them. Now, intelligibility presupposes order. Therefore, we may justifiably conclude that there exists order even behind elements of chaos.
Hence, I think it is quite certain that an ordering principle exists in the universe. The ancient Greek philosopher, Heraclitus, referred to this ordering principle as the "Logos." Classical theists, like myself, have traditionally associated the Logos with God. In fact, John 1:1 says, "In the beginning was the Logos, and the Logos was with God, and the Logos was God." Modern English translations render the Greek "Logos" as "Word." A number of attributes of the Logos can be demonstrated analytically. The Logos must be eternal, unchanging, and one.
The first two attributes are closely tied together. The Logos must be eternal, since there is no time in which it is false that "A=A" or "2+2=4." It is logically absurd for 2 and 2 to make 5, or for A to be ~A (not-A). From this it follows that the Logos must be unchanging, because it could never be the case that "A=A" could change into its negation. Finally, the Logos must be one. The reason for this is that everything with order shares in the singular attribute of intelligibility. As I mentioned in my last post, we're talking about "uniformity," not "pluriformity."
Therefore, I believe we have demonstrated the existence of an eternal, unchanging, and singular Logos that explains the order inherent in the universe.