Chapter 009 - The Immutability of God

That God is absolutely unchangeable is proved from His being the Pure Act, with no admixture of any potentiality. For the potential, strictly speaking, comes after the actual, and everything subject to change is in some degree in a state of potentiality, and capable of receiving more. Further, whatever is moved partly remains as it was, and partly goes on further, as when a thing changes from white to black, it remains in substance as it was; and hence in every change there is something which is composite; but this cannot be in God, Who is absolutely Simple. Lastly, everything moved acquires something, and attains to that which it had not; whereas God, Who is Infinite, comprehends in Himself the entire plenitude of all perfections in all beings, and cannot acquire anything more, or attain to that which He has not. He is, therefore, absolutely unchangeable. Hence, even among the ancient philosophers, truth compelled some to postulate a First Immovable Principle of all. It belongs, therefore, to God alone to be unchangeable of Himself. The creature is unchangeable through the Creator’s power, in whose hand is its existence and non-existence, for its creation and preservation depend upon the absolute Will of God. In every creature change is possible: in corruptible bodies according to their substance, and in celestial bodies according to place only, because matter’s potentiality is completed by form; hence the latter are not subject to change according to their substance, but only according to place. In the subsistent forms of the angels, who are not in potentiality to non-existence, there is a two-fold changeableness: that by which they are in potentiality to their final end, thus being subject to change as regards choice of evil instead of good; the other, according to place, whereby they can by their finite power reach to some other place. As God, therefore, is not changeable by any of these modes, He alone is absolutely unchangeable.