You: How can you possibly talk to me about God's motivations when you have not even proven to me that he exists?

Aaron: Many years ago, scientists used anomalies in planetary orbits to predict that there must be a planet beyond Uranus. They were able to derive its mass long before its discovery by seeing the effect it had on other planets. We can derive some properties of God in the same way.

You: I have no reason to derive properties of God from the state of the universe; the laws of physics seem to do just fine.

Aaron: But we can discover what properties God would have if he did exist and use these to test if he exists, just as physicists predicted where Pluto would have to be and discovered it by looking in that place.

You: I might allow you to look for certain properties God would have to have and use those to prove his existence, but I will not allow you to use those properties in a proof until they have to be proven.

Aaron: Such properties are either so obvious that they really do not need to be proven or so subtle that proving them would take more time than we have today.

You: That is ridiculous. You must either demonstrate these properties to me or cease to use them in your argument.

Aaron: Things are getting out of hand here. In the interest of peace, let me change tactics.