ABSTRACT
At least among philosophers, one of the best-known arguments for the existence of God is the one set out by Descartes in the third Meditation. The argument is a causal one, starting from Descartes’s own idea of God and proceeding to enquire into what the cause of this idea must be. Quite clearly some strong metaphysical principles are going to be needed if any such train of argument is to reach the desired conclusion, and Descartes showed no obvious reluctance in revealing at least one of them:
It is manifest by the natural light that there must be at least as much reality in the efficient and total cause as in the effect of that cause. For where, I ask, could the effect get its reality from, if not from the cause? And how could the cause give it to the effect unless it possessed it? It follows from this both that something cannot arise from nothing, and also that what is more perfect-that is, contains in itself more reality-cannot arise from what is less perfect.1
