Aquinas' Five Ways
Thomas Aquinas set out five ways or "proofs" of God's existence. IN WAY ONE, Aquinas offered the evidence of change in the world. He wrote, "Now anything in process of change is being changed by something else." Using Aristotle's idea of an Unmoved Mover, Aquinas reasoned, "If the hand does not move the stick, the stick will not move anything else. Hence one is bound to arrive at some first cause or change not itself being changed by anything, and this is what everybody understands by 'God'."
IN WAY TWO, Aquinas focused on cause and effect in the world. "Now if you eliminate a cause you also eliminate its effects, so that you cannot have a last cause, nor an intermediate one, unless you have a first." Aquinas did not believe in an infinite chain of causes and effects reaching back into eternity. "One is therefore forced to suppose some first cause, to which everyone gives the name 'God'."
IN WAY THREE, he takes up the idea of being and non-being in the world. The fact is that things exist, but they don't really need to exist. On top of that, there was a time when they did not exist, and there will be a time when they no longer exist. "Now everything cannot be like this, for a thing that need not be, once was not, and if everything need not be, once upon a time there was nothing...." Aquinas asserted that if nothing in the world needed to exist, there must have been a time when nothing existed. Logic told him that nothing can come from nothing. "One is forced therefore to suppose something which must be, and owes this to no other thing than itself; indeed it itself is the cause that other things must be." In this, Aquinas actually sounds a lot like Anselm. Both believed that objects in the world have contingent existance (they can exist, but they don't have to exist), but only God has necessary existence (God must exist to be God). If God did not exist then nothing could exist, because creation is dependent upon God's necessary existence to exist at all.
IN WAY FOUR, Aquinas concentrated on degrees of goodness and perfection in the world. "For example, things are hotter and hotter the nearer they approach what is hottest. Something therefore is the truest and best and most noble of things, and hence the most fully in being; for Aristotle says that the truest things are the things most fully in being." Aquinas went on to write, "There is something therefore which causes in all other things their being, their goodness and whatever other perfections they have. And this we call 'God'."
IN WAY FIVE, Aquinas pointed to goals and order in nature. "For their behavior hardly ever varies, and will practically always turn out well; which shows that they truly tend to a goal, and do not merely hit it by accident. Nothing that lacks awareness tends to a goal, except under the direction of someone with awareness and understanding; the arrow, for example, requires an archer. Everything in nature, therefore, is directed to its goal by someone with understanding, and this we call 'God'."
There you have the five ways or "proofs" of God's existence offered up by perhaps the most brilliant mind of medieval theology and philosphy. His ideas have been debated and criticized, but they're still around. Like most people with an "NT" temperament (I'm an INTJ for those of you interested in such things) I find that Thomistic Spirituality really resonates with me.
Now, let me ask you a question: Do you think any of these Five Ways might be helpful if you were talking to someone who didn't believe in God or wasn't sure? Which one(s) and why?