3 Things All-Powerful God Can’t Do

“For with God nothing will be impossible.”

The archangel Gabriel, who spoke those words (Luke 1:37) to the Virgin Mary, knew well the infinite power of God Almighty. Many of us gain spiritual strength and solace through thinking that with God, all things are possible. St. Thomas Aquinas, the great Angelic Doctor of the Catholic Church, was familiar with what Gabriel had said. How strange, then, that in his acclaimed Summa Theologiae, Thomas explains a few “things” that God cannot do.

Let’s examine three such “things” God cannot do (and find out why I put “things” within “scare quotes”).

1. God cannot make a circle a square. That may seem like an odd one to any of us who used modelling clay as children. How easy it was to turn something circular into a square, and vice versa, just by squishing things in or out in the right directions! Yes, but did any of us ever have luck in making a square that was also still a circle? That’s so difficult, indeed, that Thomas argued that God himself cannot do it!

2. God cannot make a thing better than it is in its essence. For example, God created humans as rational animals, living beings of body and soul, possessing intellectual powers that operate through our senses. Rationality belongs to the essence of man. If humans were endowed instantaneous knowledge like the angels, they would no longer be human beings. For a much simpler example, per Thomas, “he cannot make the number four greater than it is; because if it were greater it would no longer be four, but another number” (ST, I, Q. 25, a. 6).

3. God cannot make the past not to have been. This may seem odd to us who have read or seen sci-fi stories where people travel back in time to make what happened never have happened (like the birth of Hitler or the premature death of some great scientist). Thomas, however, favorably cites Aristotle, who wrote, “Of this one thing alone is God deprived—namely, to make undone the things that have been done” (ST, I, Q. 5, a. 5).

To begin to unravel these paradoxes, let Thomas speak for himself:

I answer that, all confess that God is omnipotent; but it seems difficult to explain in what his omnipotence precisely consists; for there may be doubt as to the precise meaning of the word all when we say God can do all things. If, however, we consider the matter aright, since power is said in reference to possible things, this phrase, God can do all things, is rightly understood to mean that God can do all things that are possible (ST, I, Q. 25, a.1).

He elaborates with Aristotle’s distinction of two ways in which a thing may be impossible. The first way is in relation to a power. Things within our human powers are possible for us (like walking), whereas things that exceed our powers are impossible for us (like flying using our bodies alone). The second way is absolute impossibility due to the relation in which terms stand relative to each other.

Impossibility in the first way cannot apply to God. God’s power infinitely exceeds human power. But to say that God is omnipotent because he can do all things possible to his power is arguing in a circle and does not really tell us anything.

So God is rightly called omnipotent in the second way of considering possibility and impossibility. “God can do all things that are possible absolutely.” In other words, God can do all things that are not self-contradictory and therefore absolutely impossible. God cannot make a square circle or create a boulder so massive that even he could not lift it. These things are absolutely impossible, since a self-contradictory thing simply cannot exist. As Msgr. Paul Glenn explains, “a contradictory thing is not a thing at all. It is a fiction in which two elements cancel each other and leave nothing. Thus, a square circle is a circle that is not a circle; that is to say, it is nothing whatever.” (That is why I put “things” in “scare quotes in our first paragraph.) It is meaningless to ask if God can make such “things,” but their impossibility does not diminish his limitless power. Rather, they manifest God’s truth, in that “a self-contradictory thing is a self-annihilating lie.”

Thomas sums it up like this: “Hence it is better to say that such things cannot be done, than to say God cannot do them.” (We might say that there is no “them” there to be done!) Thomas notes as well that this does not contradict Gabriel’s statement, that “no word shall be impossible with God,” because “whatever implies a contradiction cannot be a word, because no intellect can possibly conceive such a thing.” (I know that neither of us is God, but let’s try to conceive in our mind’s eye just what a square circle would look like. Any luck?) Further, let’s note that “word,” in the Bible translation above, comes from the Latin Bible Thomas used. If we turn to the RSV-CE translation, we read that for God no “thing,” rather than no “word,” is impossible (Luke 1:37). And so there is no logical difference—no true, non-contradictory thing is impossible for God to do.

Thomas also provides a detailed explanation in addressing why God cannot make the past not to have been. In his day (the thirteenth century), some held that God could go back in time to make events that happened not to have happened, not fully grasping the distinction between possible and impossible things. Thomas shares this profound quotation from Augustine, to the contrary: “Whoever says, if God is almighty, let him make what is done as if it were not done, does not see that this is to say, if God is almighty, let him effect that what is true, by the very fact that it is true, be false.”

Thomas himself says, “There does not fall under the scope of God’s omnipotence anything that implies a contradiction.” God is able to do all things that are non-contradictory—that is, all things that could possibly be done. Regarding all things possible, there are no limits to his power. He can raise the dead and create the entire universe ex nihilo (“out of nothing.”) But because he is truth—as Jesus Christ told us, “I am the way, and the truth, and the life” (John 14:6)—he cannot make an event that truly happened not to have happened, which would make what was true false.

To conclude on the most positive of notes, Thomas also shares an insight of great relevance to every one of us as sinners. Though even God himself cannot make it so that we had never sinned in the past, he can remove every corruption or stain of sin within our bodies and souls and enable any repentant sinner to enjoy eternal bliss with him in heaven.