One of the things that gets trotted out when someone argues that faith and reason are compatible is that many contributions to science or philosophy have been made by individuals who were religious. If faith and reason are incompatible, it is claimed, how can so many scientists and philosophers in history have been Christian (or Jewish, or Muslim, or...). But this quick argument--some philosophers are Christians therefore Christianity is reasonable, Q.E.D.--moves a little too quickly. Instead we need to ask questions about what role the idea of God plays in some particular thinker's philosophical system to assess whether his faith can be seen as truly consistent with his intellectual contribution: is the idea of God required for the system to be coherent? That is, is God a fundamental concept? Is the idea of God consistent with the rest of the system, but superfluous? Is the idea of God inconsistent with it? Because if God isn't required for, or consistent with, the wider system of thought, then it might be that all we really learn about the relationship of faith to reason from a religious philosopher is that people are capable of operating in spite of quite a lot of cognitive dissonance. One way to proceed with investigating the supposed compatibility of faith and reason would be to look at thinkers who were personally religious and see what role God plays in their systems. What kind of world do we get if we start with the assumption that God exists and work from there? In this post, I'll look at the very bizarre but apparently internally consistent system that Leibniz built on some standard assumptions about God.