In a single paragraph near the beginning of the Theodicy, Leibniz gives a very compressed version of an argument a contingentia mundi (from the contingency of the world) from which he purports to derive not just the existence of God, but several of the most important traditional divine attributes (from which, Leibniz seems to think, the other divine attributes follow). In this post, I’ll try to unpack Leibniz’s reasoning. I’m not going to do too much evaluation of the arguments, since this post will be long enough without that; I’ll just lay out the arguments as I see them and we can discuss their soundness in the comments.
First, here’s the paragraph:
God is the first reason of things: for such things as are bounded, as all that which we see and experience, are contingent and have nothing in them to render their existence necessary, it being plain that time, space and matter, united and uniform in themselves and indifferent to everything, might have received entirely other motions and shapes, and in another order. Therefore one must seek the reason for the existence of the world, which is the whole assemblage of contingent things, and seek it in the substance which carries with it the reason for its existence, and which in consequence is necessary and eternal. Moreover, this cause must be intelligent: for this existence being contingent and an infinity of other worlds being equally possible, and holding, so to say, equal claim to existence with it, the cause of the world must needs have had regard or reference to all these possible worlds in order to fix upon one of them. This regard or relation of an existent substance to simple possibilities can be nothing other than the understanding which has ideas of them, while to fix upon one of them can be nothing other than the act of the will which chooses. It is the power of this substance that renders its will efficacious. Power relates to being, wisdom or understanding to truth, and will to good. And this intelligent cause ought to be infinite in all ways, and absolutely perfect in power, in wisdom and in goodness, since it relates to all that which is possible. Furthermore, since all is connected together, there is no ground for admitting more than one. Its understanding is the source of essences, its will is the origin of existences. There in a few words is the proof of one only God with his perfections, and through him of the origin of things (Theodicy, tr. Huggard, sect. 7)
Alright, let’s see what we can make out of this. It will help to divide the argument into several stages. In the first stage, we show that a necessary being exists. In the second stage, we show that some necessary being has understanding, will, and power. In the third stage we prove that some necessary being is “absolutely perfect in power, in wisdom and in goodness.” In the fourth stage, we show that the necessary being is unique. In the fifth and final stage we show that the unique necessary being (God) is the ground of both possibility (essences) and actuality (existences). The last two stages are so elliptical and opaque that I am not going to try to reconstruct them, for now. Besides, the first three stages are enough to count as a proof of the traditional God: if sound, they would show that, necessarily, there exists a being who is perfectly powerful, perfectly wise, and perfectly good.