In the thirteenth century, St. Thomas Aquinas composed his famous five paths to God. His proofs don't depend on the Bible or divine revelation. They simply start from the world around us—trees, birds, buildings, and even ourselves. Thomas noticed that none of these things have to exist. But if that's the case, there must be some cause behind them, something grounding their existence. For Thomas and all Christians since, we know this source of all being by its ancient name—God.