We’ve proved that God can create, but left open the possibility (albeit a small one) some other being could create being. Today the proof that only God can do this. We’re very soon coming to a proof that God does not act by necessity, i.e. that He has choice.
 IT can also be shown from the foregoing that creation is an action proper to God, and that He alone can create.
 For since the order of actions is according to the order of agents, because the more excellent the agent the more excellent the action: it follows that the first action is proper to the first agent. Now creation is the first action; since it presupposes no other, while all others presuppose it. Therefore creation is the proper action of God alone, Who is the first agent…
 Further. Effects correspond proportionately to their causes: so that, to wit, we ascribe actual effects to actual causes, and potential effects to potential causes; and in like manner particular effects to particular causes, and universal effects to universal causes, as the Philosopher teaches (2 Phys.).
Now being is the first effect; and this is evident by reason of its universality. Wherefore the proper cause of being is the first and universal agent, which is God. Whereas other agents are the causes, not of being simply, but of being this, for example, of being a man, or of being white. But being simply is caused by creation which presupposes nothing, since nothing can pre-exist outside being simply. By other makings this or such a being is made: because this or such a being is made from an already existing being. Therefore creation is God’s proper action.
Notes Read “Now being is the first effect…” as “being itself, the act of existing, is the first effect…” It thus makes better sense that something in existence (say a ball) can be made this, i.e. white. Making being is making something out of nothing.
 Moreover. Whatever is caused with respect to some particular nature, cannot be the first cause of that nature, but only a second and instrumental cause. For Socrates, since he has a cause of his humanity, cannot be the first cause of human nature: because, seeing that his human nature is caused by some one, it would follow that he is the cause of himself, since he is what he is by human nature…
Notes More clues that only God can create the essence (or nature) of things. Since these are forms and forms non-material, we have more evidence of universals and metaphysical realism. The next argument takes this up more fully.
 Again. That which is caused in respect of some nature, cannot be the cause of that nature simply, for it would be its own cause: whereas it can be the cause of that nature in this individual; thus Plato is the cause of human nature in Socrates, but not simply, since he is himself caused in respect of human nature. Now that which is the cause of something in this individual, communicates the common nature to some particular thing whereby that nature is specified or individualized. But this cannot be by creation, which presupposes nothing to which something can be communicated by an action. Therefore it is impossible for anything created to be the cause of something else by creation.
 Moreover. Since every agent acts in so far as it is actual, it follows that the mode of action must follow the mode of a thing’s actuality: wherefore the hot thing which is more actually hot, gives greater heat. Consequently anything whose actuality is determined to genus, species, and accident, must have a power determined to effects like the agent as such: since every agent produces its like. Now nothing that has determinate being can be like another of the same genus or species, except in the point of genus or species: because in so far as it is this particular thing, one particular thing is distinct from another. Nothing, therefore, that has a finite being, can by its action be the cause of another, except as regards its having genus or species–not as regards its subsisting as distinct from others. Therefore every finite agent postulates before its action that whereby its effect subsists as an individual. Therefore it does not create: and this belongs exclusively to an agent whose being is infinite, and which contains in itself the likeness of all beings, as we have proved above.
Notes Gist: created things can only work with material (matter+energy) on hand. The next and last argument amplifies this and can be skipped. Though it does contain the neat word notman, which surely can find utility elsewhere these days.
 Again. Since whatever is made, is made that it may be, if a thing is said to be made that was before, it follows that it is not made per se but accidentally; whereas that is made per se which was not before. Thus, if from white a thing is made black, a black thing is made and a coloured thing is made, but black per se, because it is made from not-black, and coloured accidentally, since it was coloured before. Accordingly, when a being is made, such as a man or a stone, a man is made per se, because he is made from notman; but a being is made accidentally, since he is not made from not-being simply, but from this particular not-being, as the Philosopher says (1 Phys.). When therefore a thing is made from not-being simply, a being is made per se. Therefore it follows that it is made by that which is per se the cause of being: since effects are referred to their proportionate causes. Now this is the first being alone, which is the cause of a being as such; while other things are causes of being accidentally, and of this particular being per se. Since then to produce a being from no pre-existing being is to create, it follows that it belongs to God alone to create.