The Third Way Explained
Aquinas structured his Third Way as a logical sequence that's surprisingly easy to follow. He starts with a simple observation: everything in the natural world is contingent - it exists, but it doesn't have to exist.
Here's his reasoning: if everything is contingent, then at some point there was nothing at all. But "ex nihilo nihil fit" - out of nothing, nothing comes. Since something clearly exists now, there must be a necessary being that couldn't fail to exist.
Aquinas then tackles an important objection. What if necessary things exist, but they're all caused by other necessary things? His answer: this creates another infinite chain, which explains nothing. There must be an uncaused necessary being at the foundation.
This uncaused necessary being, according to Aquinas, is what we call God. It's the anchor that prevents the whole system from collapsing into meaningless infinite regress.
Think About It: Imagine a bicycle wheel - if you remove the central hub, all the spokes collapse. Aquinas sees God as the essential "hub" of existence.