Some have taken an occasion of going wrong by thinking that no creature has any action in the production of natural effects—thus that fire does not warm, but God causes heat where fire is present. So Avicebron in his book, The Fountainof Life, lays it down that no body is active, but the power of a subsistent spirit permeating bodies does the actions which seem to be done by bodies. But on such theories many awkward consequences follow.
If no inferior cause, and especially no corporeal cause, does any work, but God works alone in all agencies, and God does not change by working in different agencies; no difference of effect will follow from the difference of agencies in which God works: but that is false by the testimony of sense.
It is contrary to the notion of wisdom for anything to be to no purpose in the works of the wise. But if created things in no way work to the production of effects, but God alone works all effects immediately, to no purpose are other things employed by Him.
If effects are not produced by the action of creatures, but only by the action of God, it is impossible for the power of any creature to be manifested by its effect: for an effect shows the power of the cause only by reason of the action, which proceeds from the power and is terminated to the effect. But the nature of a cause is not known through its effect except in so far as through its effect its power is known which follows upon its nature. If then created things have no actions of their own productive of effects, it follows that the nature of a created thing can never be known by its effect; and thus there is withdrawn from us all investigation of natural science, in which demonstrations are given principally throughthe effect.
Some Doctors of the Moorish Law are said to bring an argument to show that accidents are not traceable to the action of bodies, the ground of the argument being this, that an accident does not pass from subject to subject: hence they count it an impossibility for heat to pass from a hot body to another body heated by it, but they say that all such accidents are created by God. Now this is a ridiculous proof to assign of a body not acting, to point to the fact that no accident passes from subject to subject. When it is said that one hot body heats another, it is not meant that numericallythe same heat, which is in the heating body, passes to the body heated; but that by virtue of the heat, which is in the heating body, numerically another heat comes to be in the heated body actually, which was in it before potentially. For a natural agent does not transfer its own form to another subject, but reduces the subject upon which it acts from potentiality to actuality.