On God as Pure Act

“I am that I am.”

Ex. 3:14

“For I am the Lord, I change not;”

Mal. 3:6

“I am the first, and I am the last.”

Isa. 44:6



Order of Contents

Articles  6+
Quotes  4
Distinction Between Passive & Active Power
Latin  4





Aquinas – Contra Gentiles, bk. 1, ‘God’

Ch. 16, ‘That there is No Passive Potency in God’

Ch. 28, ‘On the Divine Perfection’

Ch. 73, ‘That the Will of God is his Essence’

Ch. 97, ‘That God is Living’

Ch. 98, ‘That God is His Life’

Ch. 99, ‘That the Life of God is Everlasting’



De Moor, Bernard – 35. ‘God’s Knowledge, a Most Pure Act’  in Continuous Commentary, ch. 4, ‘On God’



Garrigou-Lagrange, Reginald – ‘Ontology’ & ‘Natural Theology’  in Realiity: a Synthesis of Thomistic Thought  trans. Patrick Cummins  (St. Louis: B. Herder, 1950)  pp. 11-12

Garrigou-Lagrange (1877–1964) was a French, Romanist philosopher, theologian and Dominican friar.  He has been noted as being a leading neo-Thomist of the 20th century.  He taught at the Dominican Pontifical University of St. Thomas Aquinas, the Angelicum, in Rome from 1909 to 1960.

Lagrange was the leading proponent of ‘strict observance Thomism’, which attracted wider attention when in 1946 he wrote against the Nouvelle Théologie theological movement, criticising elements of it as Modernist.

Muller, Richard – Actus Purissimus  in Dictionary of Latin & Greek Theological Terms: Drawn Principally from Protestant Scholastic Theology  1st ed.  (Baker, 1985), p. 24



Feser, Edward – ‘The Unmoved Mover’  in The Last Superstition: a Refutation of the New Atheism  (St. Augustine’s Press, 2008), pp. 91-102

Feser (b. 1968) is a Romanist, professor of philosophy and an analytical Thomist.  Here he masterfully explains in a simple and persuasive way the Cosmological argument for God’s existence, from the necessity of an unmoved mover if there is change at all.

He does not mention pure actuality till p. 96, but what leads up to it is a necessary prologue to understanding the necessity of pure actuality.

Duby, Steven J. – V.B., ‘Divine Simplicity & Divine Freedom’  in Divine Simplicity: a Dogmatic Account  PhD diss.  (Univ. of St. Andrews, 2014), pp. 247-66

Duby is a professor of theology at Phoenix Seminary.  He has degrees from Moody, Denver Seminary and the Univ. of St. Andrews.

This section is where Duby discusses actus purus the most in his work.

Marino, Matthew – ‘Vindiciae Actus Purus: A Defense of the Thomistic Doctrine’  a seminary paper  (n.d.)

Abstract: “The concept of actus purus ordinarily associated with Thomas Aquinas is among the most formidable proposals within the history of theology proper.  It serves to neutralize the main criticisms against the classical doctrine of God.  The thesis of this paper is that the doctrine of God in pure act is biblically faithful, logically necessary, and the best explanation for how the simple, timeless, immutable, and impassible God relates personally to his creatures.”

Quinones, Alan – ‘Toward the Worship of God as Actus Purus  The Masters Seminary Journal  31/2 (Fall 2020), pp. 213–30

This was published in a dispensationalist, MacArthurite journal.

“God is Actus Purus, which is to say that He is eternally all that He can be.  Potentiality is a trait of creatures, not God.  The concept of Actus Purus was first articulated by Aristotle in his argument for the unmoved mover, and through its history, the church has considered this notion a valid articulation of the absolute perfection and preeminence of God over all things.

This paper, then, explores the exegetical footing of Actus Purus. It also will seek to understand its implications for systematic theology. Careful exegesis will demonstrate that the doctrine of pure actuality is deducible from Scripture by good and necessary consequence. It is an instrument that helps to sound the unbounded perfection of God…”




Gehring, Allen Stanley – Divine Simplicity as Actus Purus  a Masters thesis  Ref  (Texas A & M University, 2005)  130 pp.

“This thesis presents a case for the traditional doctrine of divine simplicity by construing it along the lines that God exists as actus purus.  My formulation of divine simplicity draws upon the medieval insight that God is what He is in virtue of what He does in one, eternal act of will with which He is identical.

In chapter I, I survey the contemporary literature on divine simplicity.  In chapter II, I critique Alvin Plantinga’s Platonic theory of the divine attributes…  In chapter III, I provide rejoinders to all of Plantinga’s defeaters against divine simplicity…  In chapter IV, I develop a viable theory of divine simplicity, given an actus purus conception of God, and I formulate a number of arguments supporting it…  As such, I seek to demonstrate that the traditional understanding of the divine essence is something that is worthy for theists to embrace and to explore…”





Lucas Trelcatius

Quoted in Richard Muller, Post-Reformation Reformed Dogmatics, 3.221

“the principle first and pure act, of whom all things are wrought, and by whom all things are capable of movement.”


Edward Leigh

A System, or Body of Divinity…  p. 223

“In respect of the object and effects, for God does never so many and so great works, but He can do more and greater; although we must hold that God cannot make a creature of infinite perfection simply, or creatures indeed in­finite in number, for so they should be gods; for the divine power is so far exercised on the object as the passive power of the object extends itself, but infinite perfection imports a pure act.”


Francis Turretin

Institutes of Elenctic Theology, vol. 1, 3.7.4

“from his activity, because He is a most pure act having no passive admixture and therefore rejecting all composition.”


Peter van Mastricht

Theoretical-Practical Theology, vol. 2, Faith in the Triune God
(Grand Rapids: Reformation Heritage Books, 2019), p. 117

“All the attributes in God denote one most simple act.”



Etienne Gilson

The Christian Philosophy of St. Thomas Aquinas  (Notre Dame, IN: University of Notre Dame Press, 1994), p. 97.  Gilson is a Romanist.

“To say that God is absolutely simple, since He is the pure act of existing, is not to have a concept of such an act, but to deny Him, as we have seen, any composition whatsoever.”



Carl Trueman

‘The Reception of Thomas Aquinas in Seventeenth-Century Reformed Orthodoxy & Anglicanism’  in The Oxford Handbook of the Reception of Aquinas, p. 212

“Indeed the notion of God as simple, as Him being pure act, and as thus being perfect in terms of having no potentiality, is an obvious point of continuity between Thomas and the Reformed.”



On the Distinction Between Passive Power (Denied) & Active Power (Affirmed) About God


Feser, Edward – pp. 42-3  in ‘1.1.3 Divisions of Act & Potency’  in Scholastic Metaphysics: a Contemporary Introduction  (Editiones Scholasticae, 2014)

Feser here explains and illustrates the distinction with regard to everyday things, which is necessary to understand before the concept is applied to God.



Aquinas – Summa, Pt. 1, Question 25, ‘The Power of God’

Article 1

“I answer that, Power is twofold—namely, passive, which exists not at all in God; and active, which we must assign to Him in the highest degree. For it is manifest that everything, according as it is in act and is perfect, is the active principle of something: whereas everything is passive according as it is deficient and imperfect. Now it was shown above (I:3:2; I:4:1 and I:4:2), that God is pure act, simply and in all ways perfect, nor in Him does any imperfection find place. Whence it most fittingly belongs to Him to be an active principle, and in no way whatsoever to be passive. On the other hand, the notion of active principle is consistent with active power. For active power is the principle of acting upon something else; whereas passive power is the principle of being acted upon by something else, as the Philosopher says (Metaph. v, 17). It remains, therefore, that in God there is active power in the highest degree.

Reply to Objection 1. Active power is not contrary to act, but is founded upon it, for everything acts according as it is actual: but passive power is contrary to act; for a thing is passive according as it is potential. Whence this potentiality is not in God, but only active power.”


Article 3

“Reply to Objection 1. God is said to be omnipotent in respect to His active power, not to passive power, as was shown above (Article 1). Whence the fact that He is immovable or impassible is not repugnant to His omnipotence.”


Francis Turretin

Institutes of Elenctic Theology, Topic 3, Q. 21, ‘The Power of God’, p. 245

“II.  It is not queried whether passive power (which is the principle of suffering from another) may be granted in God. Since this cannot be supposed without imperfection and change, it is evident that it should be removed far from him. Nor if the generation of the Son or the spiration of the Spirit is expressed in passive terms, does it immediately follow that there is in God passive power (since this denotes a mere relation [schesin] to the persons generating and spirating). But we treat only of the active power, the principle of acting on another.”



On Possibilities & Hypotheticals

See especially, Goudriaan, Aza – ‘Samuel Rutherford on the Divine Origin of Possibility’





Zanchi, Jerome – pp. 65 (rt col, mid), 95 (lt col, mid), 102 (rt col, mid), 109 (rt col, bot), etc.  in Of the Nature of God, or of the Divine Attributes, in 5 Books  (Heidelberg, 1577)

Voet, Gisbert – p. 73 (1/3 way down), 265 (2.)  in Part 5 of the Select Disputations…  (Utrecht, 1669)



Baron, Robert – 3. ‘The 3rd Division of Real Being: it is Explicated in what Way God is Pure Act’  in Philosophy being a Handmaiden to Theology…  (1621), Exercitation 1, ‘On Being & Essence’, pp. 8-12

Voet, Gisbert – ‘The Simplicity that we have said is competent to God we prove by these reasons…’  in ‘Of the Only & Most Simple Essence of God’  in Part 1 of the Select Theological Disputations...  (Utrecht, 1648), pp. 227-9




Related Pages


Of God, the Knowledge of God & of his Attributes

On Divine Simplicity

On the Affections of God

On Absolute & Relative Attributes

That Wrath & Hatred are Not Properly in God


On the Will of God

The Revealed Will

The Decrees of God