Today we talked about two proofs for the existence of God.
First, we encountered St. Anselm's Ontological Argument for the Existence of God. It turns on the concept of greatness. Anselm asks whether we can conceive of a being-than-which-none-greater-can-be-conceived. If the concept makes sense, we can ask what such a being would be like. There may be many things we don't know about such a being, but we could know for example that it is more powerful and anything else. Otherwise, a stronger being would be even greater than the being-than-which-none-greater-can-be-conceived - but that's absurd, since we started out with the assumption that this being is at the top. No being could be smarter than the being-than-which-none-greater-can-be-conceived. If it were, that being would be greater. So now we come to the question: does the being-than-which-none-greater-can-be-conceived have to exist? It seems to Anselm that existence is a property that makes a thing greater (that's why no one would trade me a measly existent $100 for a glorious but non-existent house). If so, it seems that the being-than-which-none-greater-can-be-conceived must, by definition, exist. So this means that the being-than-which-none-greater-can-be-conceived does exist.
Notice that what Anselm is proving isn't the God of Christianity - it is a much leaner conception of God. We call this lean conception of God, God understood as a perfect being and with no personal characteristics, the "philosopher's God". Anselm has proved that something matching the characteristics of the Christian God exists. It is as if a detective proved that something with human characteristics lived in your house. That's true - but there's much more to be said, since it is you in particular, and not any human, who live there. So, as Artie pointed out, the philosopher's God is compatible with any of the monotheistic religions, and also with deism. Presumably, to show that Christianity is accurate, Anselm would have to give more proofs. But he's certainly brought us in that direction.
Then we had a quick look at some of Thomas Aquinas' "five ways". Aquinas doesn't think it makes sense to have proofs of the existence of God, because (as we saw early on), theology is a higher science than philosophy, and it doesn't make sense to prove something from a less certain science in a more certain one. However, Aquinas gives five ways of approaching what is sometimes called the cosmological argument. As we saw (and will see more of next week) the five ways show that to get a sequence of events (or effects, or possible things, etc.), you require a starting point which does not itself require explanation. In order to explain a sequence of causes, you need a first cause - and that cause has to be the sort of thing that (a) creatively causes other things and (b) does not itself require a cause. Aquinas thinks that that is what we mean by "God". Again, we have arrived at the philosopher's God.
There's more left in the passage for today. We'll pick it up in next week's class.