Why God Cannot Change: St. Thomas' Arguments

Why God Cannot Change: St. Thomas' Arguments

From Summa theologiae I.9.1: “Whether God is altogether immutable?”

“I answer that, from what precedes, it is shown that God is altogether immutable.

First, because it was shown above that there is some first being, whom we call God; and that this first being must be pure act, without the admixture of any potentiality, for the reason that, absolutely, potentiality is posterior to act. Now everything which is in any way changed, is in some way in potentiality. Hence it is evident that it is impossible for God to be in any way changeable.

Secondly, because everything which is moved, remains as it was in part, and passes away in part; as what is moved from whiteness to blackness, remains the same as to substance; thus in everything which is moved, there is some kind of composition to be found. But it has been shown above that in God there is no composition, for He is altogether simple. Hence it is manifest that God cannot be moved.

Thirdly, because everything which is moved acquires something by its movement, and attains to what it had not attained previously. But since God is infinite, comprehending in Himself all the plenitude of perfection of all being, He cannot acquire anything new, nor extend Himself to anything whereto He was not extended previously. Hence movement in no way belongs to Him. So, some of the ancients, constrained, as it were, by the truth, decided that the first principle was immovable.”

1st Argument in Syllogistic Form (From the notion of pure act)

Major: Whatever is pure act is immutable.

Minor: The unmoved mover is pure act.

Conclusion: Therefore, God is immutable.

Defense of the Argument

Proof of the Major: The unmoved mover is pure act without potency--if it had potency, that potency would have to be brought to act by something else. (Implicit in the ‘First Way’, ST I.2.3c.)

Proof of the Minor: motion or change is a transition from potency to act; whatever is not in potency cannot undergo this transition.

2nd Argument in Syllogistic Form (From the notion of motion)

Major: Whatever is in motion is a composite.

Minor: God is not a composite.

Conclusion: Therefore, God is immutable.

Defense of the Argument

Proof of the Major: Whatever is in motion must partly change and partly remain the same.  This implies composition of parts or aspects.

Proof of the Minor: It was demonstrated in ST I.3.7c.

3rd Argument in Syllogistic Form (From the notion of perfection)

Major: Whatever is in motion acquires a new perfection.

Minor: God cannot acquire a new perfection.

Conclusion: Therefore, God is immutable.

Defense of the Argument

Proof of the Major: Whatever is in motion must partly change and partly remain the same.  This implies composition of parts or aspects.

Proof of the Minor: God's perfection is infinite, as was demonstrated in ST I.7.1c.