In the introduction to this question, Aquinas points out that God’s immutability (that is, the fact that he undergoes no change) is intimately connected with His eternity. He will go on to give a thorough account of God’s eternity, and of aeviternity and time, in the next question. Before he can do that, he needs to show that there is no change in God; a fact that follows almost immediately from God being pure actuality. Although this proof is very straightforward and the question is consequently quite short, this is an important topic in itself as it shows that we have to remove God in our thinking from the realm of time.
The Thread of the Argument
A1: In the objections, Aquinas recalls that scripture sometimes appears to talk in terms of God changing in some way. However, the famous passage from Malachi 3:6 quoted in the sed contra states that “I am God, and I do not change”. It’s very easy to explain away the latter passage, for example in terms of God’s steadfastness; but to do this is to miss the direct witness to a profound fact about God that follows from His nature. In fact, as Aquinas does in the replies to the objections, we should understand the passages that appear to talk of God changing in terms of metaphor.
In fact, the implication of God’s immutability follows almost immediately from what Aquinas has already shown. One starts with the facts that God is pure actuality and that anything undergoing change must be moving from potentiality to actuality. Therefore anything undergoing change cannot be pure actuality; therefore God cannot undergo change.
Aquinas does not stop with only the one argument; he gives us another two. A thing, that is identifiable in some way as a thing, undergoing change only changes in respect of certain properties; but in order to retain its identity it must remain the same with respect to other properties. Therefore such a thing must be a composite. We know that God is not a composite in any way whatsoever (Ia.q3), therefore God cannot undergo change. Finally anything changing acquires something new; but God has the fullness of perfection already and therefore cannot acquire anything new. Therefore God cannot change.
A2: Aquinas then asks whether God is the only thing that is immutable in such a radical sense. One might think that those things that are like God in some way (e.g. souls and angels) might be unchangeable, or perhaps the blessed in heaven who have achieved their final end (after all, where would they go next?) might be unchangeable. Perhaps we should think of forms in terms of being immutable.
Aquinas shows that only God is unchangeable. At the very least we must remember that all members of creation are changeable in the sense that their continued existence depends upon God keeping them in existence. If God were to withdraw his support from a thing, that thing would go out of existence immediately. Therefore all created things can change in the sense of coming into and going out of existence.
However, in case one might think that coming into and going out of existence should be not be considered as change, Aquinas gives an enumeration of the other ways in which created things invariably undergo change. Material things can undergo substantial change when they are turned from one thing into another. They can undergo accidental change when they change their qualities. It is true that accidents that follow upon the substantial form of a thing cannot change (it is of the nature of snow to be white, for example) but this does not subtract from the general argument. In the cosmology of the day it was considered that celestial bodies could not undergo substantial change; but even they change their position. Creatures such as angels cannot change or vary in their being (other than if God stopped holding them in existence) but, as we will see in the Treatise on the Angels, they can change their place and can change their will towards or away from God (but only once). Forms vary in the way that they exist as being the form of this or of that individual being.
Summary and Handy Concepts
- God is pure actuality and therefore He cannot change in any way; He is the fullness of perfection, so there is no way in which He could change.
- All created things are susceptible to change; therefore God alone is immutable.
- It’s very easy to get completely the wrong end of the stick about God’s immutability. One might argue, as many have attempted, that if God were immutable then He must be static and impersonal; that He could not be the God that we love. But to do this is to attempt to make God in our image; He must be like us so that we can love Him. But this approach fails to see that God’s immutability follows on from His perfection and is intimately connected with Him being in eternity. God’s perfection means that every possibility, realized or not, is within God; far from being static, He provides the very being of all that is dynamic in the created world. We will see more of this as Aquinas discusses God’s knowledge and His providence later in the summa.