This argument rests unfortunately on a theory of physical nature, to which there is no counterpart in rerum natura, the theory of the 'four elements,' a physical presentation of Plato's doctrine of Ideas. Fire was taken to be ideally hot, and the cause of all heat: air ideally cold, and the cause of all cold: water ideally humid, and cause of all humidity; earth ideally dry, and cause of all dryness. The mediaeval mind delighted in this ~ocurrence to unity, ascribing all the particulars of a kind to some one source and cause, the perfect expression of that kind. Thus motion was traced to one primum mobile, political power to the Emperor, etc. The unities of nature are not so easy to discern in the light of our increased knowledge. Nature is more manifold and broken into detail than as St Thomas knew it. It is true that the sun, "warmest and brightest of beings," is the chief cause of heat and light that make human existence on earth possible; -- to the sun we owe the coal-forests, -- and we may observe that the sun is thus an image of God in the universe: but this is an analogy, not an argument. St Thomas's conclusion, so far as I see, gains no support from modern physics: but, metaphysically, it may be urged thus. -- God is ex hypothesi the ideal Being, the fulness of Being: the name 'God' means no less than that. If then there be a God at all, all other being must be derived from Him.
Of God and His Creatures: 2.15