In the action of physical causes we may distinguish between the operative agencies themselves and the subjects in which the effects of these operations are produced. Sometimes the effect is wanting in due perfection, or is in other words imperfect, physically evil, because of some defect in the agencies: the statue may be defective because the sculptor is unskilled, or his instruments bad; offspring may be weak or malformed owing to some congenital or accidental weakness or unfitness in the parents. Sometimes the evil in the effect is traceable not to the agents but to the materials on which they have to work: the sculptor and his instruments may be perfect, but if there be a flaw in the marble the statue will be a failure; the educator may be efficient, but if the pupil be wanting in aptitude or application the results cannot be “good”. All this, however, does not carry us very far, for we must still inquire _why_ are the agencies, or the materials, themselves defective. Moreover, physical evil sometimes occurs without any defect either in the agencies or in the materials. The effect produced may be incompatible with some minor perfection already in the subject; it can then be produced only at the sacrifice of this minor perfection: which sacrifice is for the subject _pro tanto_ an evil. It is in the natural order of things that the production of a new “form” or perfection excludes the actuality of a pre-existing form or perfection. All nature is subject to change, and we have seen that all change is ruled by the law: _Generatio unius est corruptio alterius_. It might perhaps be said that this privation or supplanting of perfections in things by the actualization in these things of incompatible perfections, is inherent in the nature of things and essential to their finiteness—at least, if we regard the things not individually but as parts of a whole, as members of a system, as subserving a general scheme;—and that therefore such privation should not be regarded as physical evil proper, but rather as “metaphysical” evil, improperly so called. However we regard it, it can have no other first source than the Will of the Creator decreeing the actual order of the existing universe. And the same must be said of the physical evils proper that are incident to the actual order of things. These evils are “accidental” when considered in relation to the individual natures of the created agencies and materials. They are defects or failures of natural tendencies: were these natural tendencies always realized there would be no such evils. But they are not realized; and their “failure” or “evil” is not “accidental” in regard to God; for God has willed and created these agencies with natural tendencies which He has destined to be fulfilled not always and in every detail, but in such measure as will secure the actual order of the universe and show forth His perfections in the finite degree in which He has freely chosen to manifest these perfections.