Pure Act: What It Means That God Is Fully Actual

To say that God is pure act (actus purus) is to say that He is wholly actual, with no unrealized potential in Him: there is nothing God could become that He is not already. That is why the classical tradition calls Him changeless, and why it insists His changelessness is fullness rather than stillness.

The doctrine sits underneath most of the other attributes of God. Below we define it, trace it from Aristotle through Aquinas to Scripture, state the charge that such a God must be static at its strongest, weigh the standard replies, and show how the Many Beings series answers.

Key takeaways

• Pure act means God has no unrealized potential. Everything God could be, He already is, so nothing outside Him can change or complete Him.
• Act and potency is the distinction underneath it. Creatures mix what they are with what they could become; the first being cannot, because potential is actualized only by something already actual.
• Fullness is not inertia. Aquinas denied God all passive power and assigned Him active power "in the highest degree."
• Frame-Indexed Classical Theism (FICT) keeps the doctrine whole. Where process theism and open theism give God potential so He can respond, and Craig makes God temporal since creation, FICT holds God wholly actual in His own frame and places all change on the creature's side.

What does it mean that God is pure act?

The question is simple to state. Does God have any capacity He has not yet used, any perfection He has not yet reached, any way He could still turn out? Classical theism says no, and the phrase it uses for that answer is pure act.

The phrase rests on the distinction between act and potency. Potency (or potentiality) is a real capacity to be otherwise: a block of wood is potentially a table, an acorn potentially an oak, a student potentially a scholar. Act (or actuality) is what a thing actually is: the table built, the oak grown, the knowledge gained. Every creature is a mixture of the two. It is something, and it could become something more or something less, and every change it undergoes is the passage from one to the other. That is why the distinction between potentiality and actuality has been the backbone of Christian philosophy of change since the Middle Ages.

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God, on the classical view, is not a mixture. In Him there is act with no potency to fill. As the Stanford Encyclopedia of Philosophy puts the classical claim, "To say that God is pure act is to say that anything God could be, God already is."

The doctrine carries others with it. If God has no potential, He cannot change, so He is immutable. If nothing in Him is waiting to be actualized, nothing in Him is a part that could be added or removed, which is the ground of divine simplicity. And if nothing outside Him actualizes Him, He owes His being to nothing, which is His aseity. Pull out this one doctrine and the rest of the classical account loosens.

Where does the doctrine come from? Aristotle, Aquinas and Scripture

The vocabulary is Greek. Aristotle, reasoning from the motion of the world to a first source of motion, concluded that the source could not itself be a mixture of capacity and achievement, or it would need something prior to move it. "There must, then, be such a principle," he wrote in the Metaphysics, "whose very essence is actuality." His argument has its own article on the unmoved mover.

Thomas Aquinas built the Christian doctrine of God on the idea. He argues that "the first being must of necessity be in act, and in no way in potentiality," because "whatever is in potentiality can be reduced into actuality only by some being in actuality." In the next article the phrase itself appears: "God is pure act, without any potentiality." Immutability follows at once, since "everything which is in any way changed, is in some way in potentiality." His Five Ways open with the same reasoning.

Aquinas pressed further. An essence that received existence from outside would be in potency to it, so in God the two are one: "God is His own existence, and not merely His own essence." His name for this is ipsum esse subsistens, subsistent being itself: "God is existence itself, of itself subsistent." The school that grew from this has its own entry on Thomism.

Aquinas found the same truth in the name God gave Moses at the burning bush:

God said to Moses, "I AM WHO I AM. This is what you are to say to the Israelites: 'I AM has sent me to you.'" (Exodus 3:14, NIV)

He read HE WHO IS as God's most proper name because it "does not signify form, but simply existence itself." Scripture also states the changelessness the doctrine entails. Through Malachi, God grounds Israel's survival in it: "I the LORD do not change. So you, O descendants of Jacob, are not destroyed" (Malachi 3:6, NIV). James grounds the believer's confidence in it: "Every good and perfect gift is from above, coming down from the Father of the heavenly lights, who does not change like shifting shadows" (James 1:17, NIV). In both texts God's changelessness is what His people's hope rests on.

Volume One of the Many Beings series lays the groundwork for every argument here, and you can read it free.

Is a God of pure act a living God? The question at its strongest

Here the doctrine meets its hardest question. If God cannot become anything, can He do anything?

The critic's case runs like this. Action, as we know it, is change: to act is to begin doing what one was not doing. Response is change: to answer a prayer is to do something because of what someone else did. Love, as Scripture describes it, grieves, rejoices, and turns toward the beloved. Each of these is the actualizing of a potential. A being with no potential, the critic concludes, can do none of them. The Stanford Encyclopedia's entry on divine simplicity states the classical premise: because God is simple, "he cannot harbor any unrealized potentialities, and so must be immutable." To the critic, nothing left to become sounds like nothing left to do.

Alvin Plantinga gave the worry a sharper edge. If God simply is His perfections, and perfections are properties, then God is a property, and as the same entry reports the objection, "Given that properties are abstract entities, and abstracta are causally inert, then God is abstract and causally inert."

Process theology turns the worry into a rival doctrine. Charles Hartshorne charged the tradition with a "monopolar prejudice," setting God on one side of every contrast (changeless, independent, unaffected) and the world on the other. The God of Scripture, the process theist answers, is moved by His creatures; in the Stanford Encyclopedia's summary, "God is affected by what affects the creatures."

Open theists press the same point from the Bible's narratives. In the Internet Encyclopedia of Philosophy's account of their reading, Augustine "forcefully argued for an emphasis on God's perfection and otherness from His creation that precluded genuine responsiveness on God's part to our actions," while the God of the prophets "is genuinely responsive to our concerns."

At its strongest, then, the question is not whether God changes in His character. Almost no one says He does. It is whether a God with no potential can be the living, acting, answering God of Scripture at all, or whether the doctrine describes a perfect object rather than a person.

How do classical theists and their critics answer?

Four answers dominate the discussion. Each sees something true, and each strains somewhere.

The classical answer: no passive power, all active power

The Thomist reply is that the critic has confused two kinds of power. Passive power is the capacity to be acted on, to receive, to be changed; active power is the capacity to act on another. Of the first, Aquinas says it "exists not at all in God"; the second "we must assign to Him in the highest degree." A being with no passive potency is not a being with no activity. It is a being whose activity nothing can increase.

Aristotle saw the same. His first actuality was not a frozen thing but a life: "the actuality of thought is life, and God is that actuality." Aquinas draws the conclusion for subsistent being itself: "God's existence includes in itself life and wisdom." On this view a God with no potential is not less active than His creatures but more, since nothing remains for Him to become.

The answer succeeds against the cruder charge. It strains on the next question. How does a God whose act never alters relate to a world that does? The traditional answer is that God's relations to creatures are real in the creature and logical in God, so that when the world changes, God does not. Critics hear in this a relation that is real on only one side, and they ask whether a God unaffected by prayer has been related to the one praying at all. The article on whether God can change His mind takes up that question directly.

Process theism: a God with two natures

Alfred North Whitehead and his followers answer by giving God a second side. God has a primordial nature, His eternal envisagement of every possibility, and a consequent nature, His taking in of the world as it happens. God's character is stable; His experience grows.

The strength is responsiveness: God really receives His creatures' joys and sorrows. The cost is that God is completed by the world. A God with a consequent nature needs a world to be fully Himself, cannot be the God of creation from nothing, and cannot guarantee that good will win.

Open theism: a God who chooses to receive

Open theism keeps creation from nothing and God's independence, but holds that God freely opens Himself to be affected. He responds to prayer by changing course, learns what free creatures decide as they decide it, and enters time to do so.

The strength is that prayer and relationship read exactly as Scripture narrates them. The strain is that the open God has potency after all: there are things He will know and do that He does not yet know or do, and creatures are what actualize them. The classical worry returns. Something outside God now completes Him.

The two-tier answer: Craig's God, timeless then temporal

William Lane Craig takes a middle road. In his work on time and eternity he holds that God is timeless without creation and temporal since creation. God's existence, character and purposes never change, but His relational life runs in sequence with the world, and His knowledge of what is happening now changes as the world does. Craig accordingly declines the strong doctrine of divine simplicity, objecting that the Thomist version leaves us no positive knowledge of what God is.

The strength is that Craig keeps a changeless core and an engaged God at once. The strain is what that costs him. To secure relationship he gives up strong immutability and strict simplicity, and with them the classical doctrine. The theistic personalism article follows where that road leads.

The series weighs each of these accounts volume by volume; the books are the place to start.

How Frame-Indexed Classical Theism answers: pure act is fullness, not stillness

Frame-Indexed Classical Theism (FICT) is a research program in analytic theology that dissolves classical theological dilemmas by diagnosing them as artifacts of one error: a term carried across two frames as though it meant the same thing in each. Here, process theism and open theism give God potential so that He can respond, and Craig gives God a temporal life so that He can relate. FICT gives up nothing. It holds God wholly actual and engaged with His world, because the word on which the dilemma turns has two senses.

That word is "change," and with it "act" and "potential." Each was learned in the creature's world, where to act is to begin, to respond is to alter, and to love is to be moved. In that frame the critic is right: every act of ours is the filling of a potential. The mistake is to carry that sense across, unchanged, to God. The series calls this move the Many Beings Fallacy, and this dispute is one of its clearest cases. God's nature and ours differ in kind, and a being's nature fixes the frame in which it lives. The same word, said of each, cannot be univocal.

Read in God's own frame, immutability is not stillness. Volume Four, Resolving Immutability & Interaction, puts it in one line: immutability "so understood is a perfection of fullness, not of dormancy." God does not move from potency to act because no potency in Him remains unrealized. His life is complete.

Read in the creature's frame, God's engagement is real and it unfolds. Here is the move the four answers above lack. God acts in one eternal act, and creatures receive that one act as many: as a beginning and then a history, as a prayer heard and then an answer given, as mercy to the penitent and judgment on the unrepentant. The sequence is real, and it belongs to the receiver. The change is in the creature, whose frame is succession; the act is in God, whose frame is not. Nothing in God waits on the world to complete it, and nothing in the world is unreal for that.

So FICT can say what process theists and open theists doubt any classical theist can say: a God with no potential is not an abstract object. In Volume Four's phrase, "pure act is maximal causal vitality," the living source by which every creature exists and acts. Jesus defended His Sabbath healing in exactly these terms:

Jesus said to them, "My Father is always at his work to this very day, and I, too, am working." (John 5:17, NIV)

Paul told the Athenians the same about the God who needs nothing:

"The God who made the world and everything in it is the Lord of heaven and earth and does not live in temples built by hands. And he is not served by human hands, as if he needed anything, because he himself gives all men life and breath and everything else." (Acts 17:24-25, NIV)

Each rival keeps something true. The Thomist keeps God's fullness; process theism and open theism keep the reality of God's engagement; Craig keeps both, but in a single frame, which forces him to give up part of one to keep the other. Held in two frames, neither has to be given up. The statement of FICT sets out the position in full, and the same move shows why God is the ground of being rather than one more being among the rest.

Volume Four, Resolving Immutability & Interaction, works this out for prayer, providence and creation.

Pure act under fire: five simulated attacks

We have run thousands of simulated attacks against Frame-Indexed Classical Theism, drawn from academic and peer-reviewed sources. Five of them bear directly on pure act, the doctrine where process theists, open theists and Craig each part company with the classical tradition.

Does picturing changelessness as perfect stillness make God inert?

Here's one of those attacks and how the Many Beings framework would address it.

The attack comes from the literature on divine simplicity, which insists that God's changelessness is fullness of being. A later volume of the series, on physics, reads the limits of the created order as pointers to God's attributes. One of those limits is absolute zero: perfect stillness, a state with no motion left to lose, which no finite process can ever reach. The volume says the unbounded this wall points toward is the immutable God. Stillness is a privation, the absence of motion. If God's changelessness is modelled on the most motionless state imaginable, God becomes the limit of a running down, which is inertia, and the series has contradicted its own claim that God's changelessness is fullness.

The defense is that the volume never reads a limit as a measurement of God. Its first rule for every such mapping is to read each wall "by negation, never by measurement," and its second is that no physical constant is ever said of God. The cold floor marks where the finite gives out; it shows the infinite only the way a cut-out shows an outline, by absence. What lies past that floor is not a colder state. It is a rest that is "a nature and not a temperature," and Volume Four had already defined that changelessness as "a perfection of fullness, not of dormancy." The objection is to a picture the series explicitly forbids.

Is a God of pure act simply unintelligible?

Here's one of those attacks and how the Many Beings framework would address it.

R. T. Mullins, in The End of the Timeless God (2016), presses the objection that the classical God, wholly actual and timeless, is incoherent. Strain as we may, he argues, we cannot form a working conception of a life that is complete without any succession. Craig voices a related worry when he says the Thomist doctrine leaves us no positive knowledge of what God is. A doctrine no one can conceive, on this view, is a doctrine no one can coherently believe.

The defense grants the strain and denies the inference. Volume Five, Resolving Potential vs Actual Infinity, agrees that the finite mind cannot picture a complete life without succession, and adds that it should not be able to. Unintelligibility to the creature's frame is exactly what a difference in kind between Creator and creature predicts. The strain is the signature of the gap, not evidence that what lies beyond it is incoherent.

Knowing truly is not the same as comprehending. Aquinas said as much: "our intellect cannot know the essence of God itself in this life, as it is in itself." The believer who knows God as just, merciful and wise knows Him truly, because these are the faithful ways His one act reaches a finite mind. What no creature does is picture that act whole. We affirm pure act truly without forming a working image of it.

Does calling God's capacity infinite turn eternity into a quantity?

Here's one of those attacks and how the Many Beings framework would address it.

This one comes from a Thomist. In explaining why God is not in time, the series contrasts a finite mind, which can take in reality only a little at a time, with God, who is not limited in that way. The Thomist objects that this makes God's eternity the top of a scale of capacity, the largest possible amount of what creatures have a little of. Aquinas forbids exactly that. He distinguishes the infinity of form from the infinity of quantity and rules: "the infinite of quantity is the infinite of matter; such a kind of infinite cannot be attributed to God." An eternity grounded in unlimited capacity would make God the biggest creature, not the Creator.

The defense is that the series grounds God's eternity where Aquinas does. Volume Three, Resolving Time & Eternity, states it in his terms: because God is pure act, His infinity is formal and qualitative, not a quantity He must possess, and He is the infinite source, not a receiver metered by any limit. The language of limited capacity describes the creature's side: why a finite mind meets reality in sequence. The infinity of God is the absence of all limit in the One whose being is underived, not an endless amount of anything.

Does "actualized for the Creator" mean God passes from potency to act?

Here's one of those attacks and how the Many Beings framework would address it.

This is friendly fire, the kind of objection Paul Helm's defense of God's timeless eternity would raise against a careless ally. Volume Three says that the future stays open for the creature while remaining "a settled, actualized reality for the Creator." "Actualized" and "settled" are completion words. They describe the result of a process: something that was potential and then became actual. If history becomes actual for God, God has passed through a change, from a state in which it was not yet real to Him to one in which it is. That is potency in God, the one thing the doctrine forbids.

The defense is that the word describes the world's side, not God's. For God the whole of created history is tenselessly actual: real, complete and known in one act, with no earlier state in which it was not yet so. Every actualizing, every passage from could-be to is, belongs to the creature's frame, where the future really is open and really becomes settled. God has no passive potency to be actualized, which is just what Aquinas meant in saying that passive power "exists not at all in God." The settling is the creature's; the eternity is God's, and the eternity of God article sets out the difference.

If God is one act, was creation necessary?

Here's one of those attacks and how the Many Beings framework would address it.

Mullins presses this in his case against divine simplicity, "Simply Impossible" (2013). A being of pure act has no plurality of acts, so His creating of the world must be identical with His one act, which is identical with Himself. God exists necessarily, so His act is necessary, so creation is necessary. And, as he asks in The End of the Timeless God, what distinguishes the eternity in which God has created from the one in which He has not?

The defense, set out in full in the article on modal collapse, is that necessity holds of the act taken in itself. To call that act "the creating of this world" is to describe it by its effect, and the effect could have been otherwise. Nothing in God differs between the world in which He creates and the one in which He does not; the difference lies wholly on the creature's side. That is not an embarrassment. It is what free creation looks like when nothing outside God is allowed to complete Him.

If these replies raise more questions than they settle, Volume One is the place to test them, and it is free to download.

Frequently asked questions

What is the difference between act and potency?

Potency is a real capacity to become something; act is what a thing actually is. Wood is potentially a table and actually wood. Every change is a passage from potency to act, which is why the distinction explains change. Creatures are always a mixture of act and potency. God, on the classical view, is pure act, with no potency at all.

What does ipsum esse subsistens mean?

Ipsum esse subsistens is Aquinas's Latin for "subsistent being itself." It means God does not receive existence as a gift from outside; He is His own existence. It is the same truth as the doctrine of God's full actuality, stated in terms of being, and the aseity article develops it.

Is pure act the same as divine simplicity?

They are closely tied but not identical. Pure act says God has no unrealized potential. Simplicity says God has no parts of any kind. Each implies the other, because a composite being has parts that could change, and a being with potential is composed of what it is and what it could be. The divine simplicity article takes up the objections.

If God is pure act, can He answer prayer?

Yes. God answers prayer in the one eternal act by which He wills both the prayer and its answer, and the prayer is a real cause within that act. The change happens in the world, where the answer arrives after the asking; nothing in God has to change for the prayer to matter. The article on whether God can change His mind follows this through the relenting texts.

Is pure act a biblical idea or Aristotle's?

The vocabulary is Aristotle's; the truth it names is biblical. Aquinas used the term to state what Scripture already teaches: God does not change (Malachi 3:6), needs nothing (Acts 17:25), and gives His name as "I AM WHO I AM" (Exodus 3:14).

Where to go from here

The charge against pure act was always that fullness looks like stillness from where we stand. It does, because we only know what life is by watching things change. The God of Scripture is more alive than His changing creatures, because nothing in Him is waiting to be realized.

Volume One sets out the method behind every answer on this page, and it is yours free. The series carries the same method into evil, time, changelessness and infinity.