20. But it is necessary also to meet the more speculative and metaphysical difficulties which have been mentioned, and which concern the cause of evil. The question is asked first of all, whence does evil come? _Si Deus est, unde malum? Si non est, unde bonum?_ The ancients attributed the cause of evil to _matter_, which they believed uncreate and independent of God: but we, who derive all being from God, where shall we find the source of evil? The answer is, that it must be sought in the ideal nature of the creature, in so far as this nature is contained in the eternal verities which are in the understanding of God, independently of his will. For we must consider that there is an _original imperfection in the creature_ before sin, because the creature is limited in its essence; whence ensues that it cannot know all, and that it can deceive itself and commit other errors. Plato said in _Timaeus_ that the world originated in [136] Understanding united to Necessity. Others have united God and Nature. This can be given a reasonable meaning. God will be the Understanding; and the Necessity, that is, the essential nature of things, will be the object of the understanding, in so far as this object consists in the eternal verities. But this object is inward and abides in the divine understanding. And therein is found not only the primitive form of good, but also the origin of evil: the Region of the Eternal Verities must be substituted for matter when we are concerned with seeking out the source of things. This region is the ideal cause of evil (as it were) as well as of good: but, properly speaking, the formal character of evil has no _efficient_ cause, for it consists in privation, as we shall see, namely, in that which the efficient cause does not bring about. That is why the Schoolmen are wont to call the cause of evil _deficient_. 21. Evil may be taken metaphysically, physically and morally. _Metaphysical evil_ consists in mere imperfection, _physical evil_ in suffering, and _moral evil_ in sin. Now although physical evil and moral evil be not necessary, it is enough that by virtue of the eternal verities they be possible. And as this vast Region of Verities contains all possibilities it is necessary that there be an infinitude of possible worlds, that evil enter into divers of them, and that even the best of all contain a measure thereof. Thus has God been induced to permit evil.