Let’s start with the Contingency argument.
Felix the cat is a contingent reality. In other words, the reason that Felix exists is because certain, prior states of existence caused—and concurrently cause—Felix to be. For example: from the procreative act of Felix’s parents, to the concurrent existence of the earth’s atmosphere, electromagnetic fields and so on, some conditions explain what brought Felix into existence, whereas other conditions explain what *keeps* Felix in existence.
Therefore, let us ask a simple but provocative question: could everything in reality be dependent upon some prior set of conditions being fulfilled in order to exist?
The answer to this question is, emphatically, “no.” The reason is because to say that all of reality is contingent is also to say that all of reality depends upon the impossible fulfillment of conditions in order to exist. Yet, beyond “all of reality” there is literally nothing and from nothing comes nothing. Therefore, reality could never exist, which is absurd because here we are.
And so, we are forced to conclude that not everything in reality is contingent. While most everything we encounter is contingent, there must be at least one non-contingent, and therefore necessary, reality in order to explain why any contingent thing exists instead of nothing.
If there is a necessary reality, then the next question is what could this necessary reality be? Here’s one way we can figure that out: we distinguish between the “essence” and “existence” of something.
Something is contingent insofar as its essence — the “what-ness” of something — is truly distinct from its existence — the “is-ness” of something. In other words, when we talk about what something is—whether a lion, a mouse, or an electron—we’re referring to its essence. And when we talk about the fact that something “is”—which we determine through observation—we’re talking about its existence.
Now, we can observe that for any limited and finite being—whether cats, electrons, or platypuses—there is a real distinction between a thing’s essence and existence. The fact that such things exist but didn’t previously exist, or could expire from existence in the future, supports this notion of a “real distinction.”
Here’s another way to think about it: The “what” of any finite, limited reality doesn’t determine its inclusion in reality; or doesn’t cause it’s existence.
So whatever is limited in being was made by something else to exist in that limited and finite “mode” of being.
We have said that not everything can be contingent and that whatever is limited is contingent. Therefore, not everything can be limited in how it exists. And since there must be at least one necessary being, there must be at least one (qualitatively) unlimited being (which are one and the same): specifically, a being with no essential set of limits, restrictions, or boundaries on what it is, what it knows, or what it can do. A being whose essence is existence as such. And that we would call “God.”
Now, why call such Being “God?”
For one, this necessary reality must be the ultimate, grounding explanation for why anything else exists—it is, in short, the ultimate cause of everything apart from itself. And surely, if God is anything, God is the ultimate cause of everything else which exists.
But even more, we can ride out the implications of what it means to be qualitatively unlimited and eventually arrive at various divine attributes. For example, to be unlimited in power (that is, the ability to produce an effect) is to be omnipotent. Also, to be unlimited in knowledge (itself a power) is to be omniscient. Furthermore, to be free of any limits with respect to space and time—since to be restricted in existence to some material form, place, or time, is obviously a limit—is to be immaterial and eternal.
In other words, we have deduced an all-powerful, all-knowing, immaterial, and eternal being which exists in virtue of what it is, and which provides the ultimate explanation for why anything—including itself—exists. While further arguments are required to prove Christianity, most would agree everything just described is a common (though minimal) conception of God.
[Example of The Contingency Argument in a conversation]
So there you have one version of the argument from contingency. Remember to emphasize how the contingency argument is not asking what brought things into existence some very long time ago (that’s the next argument), but rather, what keeps anything in existence here and now. This argument demonstrates not only God’s existence, but God’s providence for everything he’s made, since he is continually donating “being” to everything else in reality.