What are Aquinas's five ways, and do they prove God exists?

The five ways are Saint Thomas's five arguments from motion, causation, contingency, degrees of perfection, and design, and while the Church teaches that God's existence can indeed be known with certainty by natural reason, the fifth way, the argument from design, is the one I would actually put in front of an unbeliever. Take the five in order as Thomas gives them in the Summa. Things are in motion, and whatever is moved is moved by another, so there must be a first mover. Things are caused, and the chain of efficient causes cannot run back infinitely, so there must be a first cause. Things exist contingently, they come and go, so there must be a necessary being. Things display degrees of perfection, better and worse, so there must be a maximum. And things without intelligence act toward an end, so there must be an intelligence directing them. That last one is the teleological argument. Before I say anything critical, let me be clear about where the Church stands, because that is not negotiable. Vatican I declared: "If anyone shall have said that the one true God, our Creator and our Lord, cannot be known with certitude by those things which have been made, by the natural light of human reason, let him be anathema" (Denzinger 3026). Vatican II repeated it in Dei Verbum 6: God "can be known with certainty from the created world, by the natural light of human reason," citing Romans 1:20. So the Catholic position is that the existence of God is demonstrable from creation. Anyone who says reason cannot get you there is under an anathema. Thomas's method deserves respect. He poses a question, marshals every objection he can find, then answers them one by one. It is thoroughly Aristotelian, it is rigorous, and the Church has rightly honored him for it. But I do have my gripes with the five proofs, and I will state them plainly. They are physical. Look at them: cause and effect, motion, necessary being. They read almost like a physics lesson. That is because Thomas got the framework from Aristotle, whose whole system runs on motion and rest, with rest as the perfection and motion as the imperfection, so that you need a first mover who is himself ultimately at rest, moving everything else by cause and effect. A moves B, B moves C, and so on, and it cannot be infinite. Is that really the ultimate way to view our existence, as billiard balls, one struck and knocking into the next? My second gripe follows from the first. This makes Thomas's system deterministic. I have talked with Thomists and they confirm the point: the first mover does his job by setting one thing in motion, which is designed to set the next in motion, and there is no stopping the chain. But the Church has always insisted on free will and has never let go of it, and I do not see that Thomas's metaphysics has room for it, except to say that free will is somehow accounted for within the cause and effect. That is semantics unless you can explain how a genuinely free will, not itself determined from the beginning, fits inside a deterministic chain. I am not claiming anyone else has solved it either. Nobody has. But we still have two sides of the fence to deal with. The same problem surfaces at the top of the chain. Was God free not to create? Could he have gone on for all eternity as the Trinity alone, without angels or men? If everything is determined by the first cause and its effects, the Thomist has trouble answering. I say God was as free to create the world as he was not to create it. He chose. Nothing determined him. There is no law standing behind God telling him what to do. So the five proofs put limits on God. That is not an indictment of Thomas personally, it is the nature of philosophy and metaphysics. Push far enough and you reach a dead end, or you start saying things you cannot verify. Most of the time Thomas verified well. But history bears the limitation out. Kant's Critique of Pure Reason became the popular critique against the five proofs, and between Kant on metaphysics and Newton on physics the modern world decided it could bypass the Church altogether. Which brings me to the one I would actually use. The argument from design is probably the best argument for the existence of God, and the reason is that it is Saint Paul's argument. In Romans 1:18-20 he says the invisible things of God, his eternal power and Godhead, are known by what is seen in nature, and he concludes that men are therefore without excuse. We know instinctively that this universe runs like a ticking clock, that there is no chance behind it whatever the evolutionists say. Even secular scientists who call themselves intelligent design theorists can see it just by looking. Notice that Paul's argument presupposes that men already know God exists. On that reading there are no atheists, only liars, and that is precisely why God can justly judge them. One last caution, and it applies to every one of these proofs. Reason is a pathway to knowledge, not absolute knowledge itself. If your data is faulty or incomplete, your reasoning suffers accordingly, and we live in a fallen world where reason gets bent to evil ends as readily as to good. The only way to know your reason is on the right road is to keep checking it against the revelation God has already given. Reason is a help. It is not an absolute.