If asked, 'Why does the train start at 6.30?' I should answer, 'Because the traffic manager has so arranged it.' He might have taken the train off, or put it at another hour, or, with the concurrence of the Directors, have suspended traffic altogether. The Time Tables represent the Manager's will: yet by no means his arbitrary will. A Time Table drawn up at hap-hazard would result in a block of the whole line: it would not work. The Time Tables consequently are drawn up with much care and forethought for the natures of trains and the exigencies of traffic. The Manager controls actualities, but not possibilities and conveniences. He must make his actual appointments tally with what he finds possible and convenient.
In like manner all actuality in creatures depends on the mere will of God. And God need not will to create anything at all. He might have acquiesced in His own existence, with nothing but Himself alone in any way existing. So says St Thomas, and so the Catholic Church, in opposition to the determinist idealism of Hegel, who makes the universe and its on-goings consist of the irreversible thoughts and thought-processes of Deity. On the other hand God's power of creating is not an arbitrary power to create anything and everything that a foolish fancy may call up. He cannot give reality to intrinsic absurdities. He cannot, we may venture to think, create a race of mortal men without stomachs, or animals whose natural food should be stones, or a circle having the properties of a cycloid, or a politician licensed to lie. If He creates, He must create according to the eternal exemplars, the natures of things, as He views them in order of possibility in Himself. These eternal exemplars, or 'intelligible essences' as the schoolmen call them, represent whatever of truth there was in Plato's Ideas. They are founded upon the divine nature, as imitable outside of God: they are discerned in the divine intellect: they do not depend, formally speaking, on the divine will. God's will and decree does not make and unmake possibilities. These intelligibilia, on the lines of which creation must take place, if creation there is to be at all, are treated of in B. I, Chapp. XLIX-LIV. They were ignored by the ultra-Nominalists, who took all meaning out of the phrase 'the nature of things,' and, like those 'doctors of the Mohammedan law' whom St Thomas mentions, ascribed all events without distinction to the arbitrary will of the Creator.
With these archetypal Ideas, according to which creation is laid out, and athwart of which it cannot run, we are very imperfectly acquainted. Consequently our predication cannot travel far, when we undertake to pronounce what things are intrinsically possible and what impossible, what things absolutely God could do, and what things He absolutely could not. More things probably are intrinsically impossible than we are aware of. Among the meshes of this necessary system of the nature of things (a necessity founded upon the divine nature itself) the divine will ranges free, electing to actualise this possibility in creation, and to leave that unactualised.
From this chapter of St Thomas I have been constrained to excise much obsolete physics. To examine the plan of creation, in an age when men knew nothing of physical nature, microscopic and telescopic, molecular and sidereal, beyond what their unassisted senses could detect, and knew that little ill, -- was a laudable effort, but could lead to no more than provisional results. A modern Aquinas, dwelling, as St Thomas loved to dwell, on the variety of creation and the differences of things, cannot but feel himself in face of the question, how all these differences arose; whether they were explicit in the first creation, or whether, out of a creation originally homogeneous, things came to be differentiated by a primitive plastic power, called Evolution, which has turned out an oak, or a sycamore, to be head and representative of one line of development, and a lion, or an eagle, of another. And, if he chooses Evolution, he will have to consider the part of God's providence therein.
This chapter should be read in the light of the teleological Psalm ciii, and of St Thomas's own declaration of his purpose in B. II, Chap. IV. In the untranslated portion occurs this curious aphorism: "The first thing aimed at in creatures is their multiplication (prima ratio in creaturis est eorum numerositas), and to the gaining and securing of this end all things else seem to be subordinate."
Of God and His Creatures: 3.97