Now, it seems difficult for some people to understand how natural effects are attributed to God and to a natural agent.
 For it does not seem possible for one action to proceed from two agents. So, if the action whereby a natural effect is produced proceeds from a natural body, it does not proceed from God.
 Again, when a thing can be done adequately by one agent, it is superfluous for it to be done by many; in fact, we see that nature does not do with two instruments what it can do with one. So, since the divine power is sufficient to produce natural effects, it is superfluous to use natural powers, too, for the production of the same effects. Or, if the natural power adequately produces the proper effect, it is superfluous for the divine power to act for the same effect.
 Besides, if God produces the entire natural effect, then nothing is left of the effect for the natural agent to produce. So, it does not seem to be possible to say that God produces the same effects that natural agents produce.
 However, these points present no difficulty, provided the things previously established be considered. In every agent, in fact, there are two things to consider: namely, the thing itself that acts, and the power by which it acts. Fire, for instance, heats by means of heat. But the power of a lower agent depends on the power of the superior agent, according as the superior agent gives this power to the lower agent whereby it may act; or preserves it; or even applies it to the action, as the artisan applies an instrument to its proper effect, though he neither gives the form whereby the instrument works, nor preserves it, but simply gives it motion. So, it is necessary for the action of a lower agent to result not only from the agent by its own power, but also from the power of all higher agents; it acts, thus, through the power of all. And just as the lowest agent is found immediately active, so also is the power of the primary agent found immediate in the production of the effect. For the power of the lower agent is not adequate to produce this effect of itself, but from the power of the next higher agent; and the power of the next one gets this ability from the power of the next higher one; and thus the power of the highest agent is discovered to be of itself productive of the effect, as an immediate cause. This is evident in the case of the principles of demonstration, the first of which is immediate. So, just as it is not unfitting for one action to be produced by an agent and its power, so it is not inappropriate for the same effect to be produced by a lower agent and God: by both immediately, though in different ways.
 It is also evident that, though a natural thing produces its proper effect, it is not superfluous for God to produce it, since the natural thing does not produce it except by divine power.
 Nor is it superfluous, even if God can by Himself produce all natural effects, for them to be produced by certain other causes. For this is not a result of the inadequacy of divine power, but of the immensity of His goodness, whereby He has willed to communicate His likeness to things, not only so that they might exist, but also that they might be causes for other things. Indeed, all creatures generally attain the divine likeness in these two ways, as we showed above. By this, in fact, the beauty of order in created things is evident.
 It is also apparent that the same effect is not attributed to a natural cause and to divine power in such a way that it is partly done by God, and partly by the natural agent; rather, it is wholly done by both, according to a different way, just as the same effect is wholly attributed to the instrument and also wholly to the principal agent.
Next - CONTRA GENTILES - BOOK THREE: PROVIDENCE -Chapter 71 THAT DIVINE PROVIDENCE DOES NOT ENTIRELY EXCLUDE EVIL FROM THINGS