Leibniz on Necessary Being
What, asks Leibniz, sufficiently explains a contingent being? “Contingent” here simply means something that could have been other than it is. The entire composition of the universe, the total aggregate of substances throughout space and time, are all contingent. There are other possible things, he reasons, but there are also other possible universes that could have existed but did not. All the many contingent things in the universe, he concludes, do not sufficiently explain themselves. There must be, Leibniz insists, something beyond all the contingent things which explains them, something which is itself necessary and therefore requires no explanation other than itself.
God, Leibniz concludes, is the necessary being which provides the sufficient explanation of all contingent things–why the universe is the way it is rather than otherwise. To this point in Leibniz’ reasoning, God’s necessity is the only aspect proffered (there is little religious or theological signification in this initially unembellished metaphysical concept). God as a being may be necessary, but if the contingent universe were a mere random or arbitrary act of God, then God would not comprise the required explanation of all things.
God must not only be necessary but also the fount of the intelligibility of all things. It must be possible, therefore, to inquire into the reasons God had for creating this universe that actually exists rather than some other. And if we are to explain the lucidity of the universe by God, then God must have such comprehension that God could be said to know what it is that is being allowed to exist–that is, God must be able to grasp whole concepts and to see at once the total demonstration of things. God so far is therefore (1) a necessary being, (2) the explanation of the universe, and (3) the infinite intelligence.
[paraphrased from www.iep.utm.edu/leib-met/#H5]