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The following query was raised on the review published on 9th October 2008:

“To have a potency to become something in Aristotelian/Thomist teaching does not mean to have the other higher substantial form within it.  In a substantial change a new form is substituted for the old form.  If earth could have the potency to become Adam, could not a lower form have the potency to become a higher form (obviously with the intervention of God)?”

It is appropriate to analyse the realities of act and potency.[1]   It should first be noted that neither act nor potency can be properly defined because each is one of the first (and simple) notions.  St Thomas addresses this point in his commentary on Book IX of Aristotle’s Metaphysics.

Next, as terms, act and potency are not univocal, or equivocal, but analogous.  This means, using the terminology of Logic, that when either is said as a predicate of its inferiors, it signifies not a simple similitude between them, but some sameness and some unsameness, with more unsameness than sameness.  This can be illustrated with the example of another simple notion, good.  Good cannot be defined: it can only described—“that which all things appetise”.  Good when said of a meat pie, when said of a dog, when said of a man, when said of a saint, and when said of God, signifies (in each of these logical inferiors) something same, and something unsame.  The reader will see immediately that the unsameness is much greater than the sameness.[2]   So when act, for example, is said of the essence of water, of the essence of man, and of God’s essence, it signifies in each something more unsame than same.

Thirdly, it must be understood that act and potency constitute the most fundamental division of actual being that can be made.  Their distinction explains the imperfections of mobility, of dependence in causing, of contingency in existence, of limitation of perfection, and of natural order towards end.  It explains the imperfections on the score both of essence (essentia) and existence (ens).  Thus, on the score of essence, bodies are substantially mutable, spiritual souls are substantially finite (limited), and accidents are imperfect, for they are many and specifically distinct.  And on the score of existence, substances (whether corporal or spiritual) since they are contingent, have be (existence) not from self, but from another; and accidents have be not in themselves but in another, i.e., in substances.

From its (Latin) nominal definition actus signifies “does-[be]-ness”.  The word is derived from the Latin verb to do or to act, ago agere.  So act signifies in the first place, operation, or the act of operation.  Next, there is a transferred meaning where act signifies the form whereby some essence is determined in its species, as when we say that something “does be” water, or gold.  This is the act of essence, or essential act.  Thirdly, since every operation presupposes existence, (agere sequitur esse—do follows be), act is taken to designate be, or existence.  When we say that something, e.g. water, exists, we are saying that water “does-be”.  Here act signifies the act of existence, existential act.  Now, every act, as St Thomas says, is a certain perfection.[3] Thus act signifies perfection.  It is that whereby something intrinsically is perfect.[4]

From its (Latin) nominal definition potentia signifies “can-be-ness”, while from its understanding as a species of power it signifies “can-do-ness”.  These two indicate that potency can be either active or passive—in the one case capacity for acting, in the other capacity for receiving.  Thus fire, with its capacity to burn, the plant with its capacity to nourish itself, and man with his capacity to understand, are each examples of active potency.  Whereas, water with its capacity to be hot or cold, and primary matter with its capacity to be water, or fish, or any other material thing, are examples of passive potency.  St Thomas deals with potency in his commentary on Aristotle’s Metaphysics Book V, lecture 14.

“Just as every agent or mover moves something other than itself and acts in something other than itself, so too every patient is acted upon by something other than itself.”

Passive potency is then,

“the principle of movement or of change from another inasmuch as it is another.”  [Ibid. n. 956]

Potency is the subject of act—is actuated by act.  It is imperfection, but not imperfection in the sense of mere absence or privation of perfection (as the lack of speech in a tree, or the lack of a constant temperature in water).  For absence or privation of perfection is non-being existing only in mind (mental being).  But, on the contrary, potency is real capacity for perfection, or natural appetite for perfection.  Hence, potency is the intrinsic reason or principle of perfectibility.  Potency is per se and essentially ordered towards act.

The Appendix to this paper sets out the various modes of act and potency.  Those who study that material will see that passive potency can be either pure or non pure (mixed).  In the present discussion we are concerned with those parts of mixed passive potency called natural and obediential potency.

Natural potency is that potency to which the subject is per se and essentially proportionate.  It is specified from the act whereof it is receptive.  Taken relatively to the power of the sun, water is proportionate to be hot.  Taken relatively to the power of combustion, primary matter is apt to assume a new natural form as when that of wood is replaced by that of carbon, or hydrogen and oxygen are replaced by water.

Obediential potency, in contrast, exceeds the natural potency of the subject.  It is specified not from the act whereof it is receptive, but from the agent whereof this act is the effect.  It is determined by the power of the agent acting.  The more powerful the agent, the higher the potency to which the subject can be raised.

Dr Austin Woodbury, quondam Regent of Sydney’s Aquinas Academy[5] , illustrated the distinction between these two with the mineral, marble.  Marble has a natural potency to be split and, under the operation of natural influences (e.g., earthquake; rock fall), it will manifest this natural potency.  But it has also an obediential potency which enables it to be split artistically.  A sculptor can, depending on his skill, use this potency to produce a passable image of some living creature or a work of majesty like Michelangelo’s David.  The greater the artist, the higher the potency to which the subject material can be raised.  It is in virtue of obediential potency, the Church teaches, that mere men are raised by God to the heights of sanctifying grace.

For natural agents there is a limit.  There can be no obediential potency to an elevation which would destroy the nature to be elevated.  Marble can be elevated to this, that it be a statue of Napoleon, but not to this, that it be living marble, or knowing marble.  Likewise, as St Thomas says,

“[s]ense, since it is utterly material, can in no manner be elevated to something immaterial.  But our intellect, or the angelic intellect, can be elevated by grace beyond its own nature to something higher.” (Summa Theologiae I, 1. 12, a. 4, ad 3; and cf. Contra Gentiles III, 54)

Hence, there is pre-required in the subject a non-repugnance to the height to which the agent seeks to raise it.  This limitation does not, however, apply to God, since His power is infinite.  Obediential potency to God does not presuppose any natural potency.  As John the Baptist remarked exasperatedly to the Pharisees and Sadducees, “God can raise up children for Abraham from these stones.” [Matt. 3: 9]

*                                               *

With this preliminary work out of the way, let us return to the question.

“To have a potency to become something in Aristotelian/Thomist teaching does not mean to have the other higher substantial form within it.  In a substantial change a new form is substituted for the old form.  If earth could have the potency to become Adam, could not a lower form have the potency to become a higher form (obviously with the intervention of God)?”

“It”, the subject of the first sentence, the writer leaves (quite understandably) fairly vague.  This “it” is not a hypothetical existing substance (let’s call it water), but the primary matter which, combined with the appropriate form, makes it be water.  The first sentence is true, then, provided the identity of the subject is spelt out and a one word rider is added, or is understood as added, as below.

For primary matter [t]o have a potency to become something in Aristotelian/Thomist teaching does not mean to have the other higher substantial form within it  actually.”

Let us say the hypothetically higher substantial form is that which would make it be a fish.  The potency (passive potency) to be a fish is not in the water.  It is in the primary matter of which the water is (for the moment) constituted.  That potency is a present reality in the primary matter.[6]   It is, incidentally, this universality of the potency of primary matter which is the reason why all material things corrupt.  Primary matter is, in a sense, always wanting to be something else!

Now let us look at the last sentence:

“If earth could have the potency to become Adam, could not a lower form have the potency to become a higher form (obviously with the intervention of God)?”

There are matters to be clarified here.  First, by “Adam” the writer must be taken to mean “Adam’s body inasmuch as it has life and existence”.  Adam’s soul (as the form of his living body) is included, but not its spiritual (i.e., immaterial) reality.  Also, by “earth” he must mean what we call in metaphysics “secondary matter”; that is, primary matter in combination with the substantial forms of the elements—calcium, carbon, oxygen, hydrogen, nitrogen, sodium, potassium, etc.—and the molecules formed from their combination essential to any living body.

Form (substantial form) is that which determines matter to be this thing or that.  Every form, as said above, is a species of act—the determinate actuation of a potency.  When matter ceases to retain one substantial form in favour of another the form is not elevated or altered but, as the writer has noted, replaced.  It may be replaced by a higher form—as the transient forms of the gametes of male and female animal are replaced by the soul of the embryo offspring.  It may be replaced by a lower—as on its death the body of the animal resolves into its native elements, calcium, carbon, oxygen, hydrogen, nitrogen, sodium, potassium, etc. and their compounds.   But the form does not admit of elevation or degradation because it is by essence not something determined but something that determines.  For “every act is a certain perfection.”

That we should conceive of natural substantial form as if it could undergo alteration is an effect of the subjectivist world in which we live.  We observe a computer program modified and improved: Windows 98 becomes Windows 2000, then Windows XP.  A successor imports modifications to an earlier program.  If this can occur in the world of artifice (human art), why cannot it occur in nature?  The reason is that an artificial form is not like a natural form.[7]   Every work of human art is necessarily imperfect.  But the works of God are, all of them, perfect. [Deut. 32: 4; Ps. 17: 31]  Descartes sought to explain the majesty of those works with a fatuous mechanicism which trivialised the Divine influence.  Darwin brought that explanation to its logical conclusion.  He removed the Divine influence![8]

St Thomas held the view (under the influence of the biology of his day) that from the time of conception in the womb and prior to delivery the human being has a succession of souls—first a vegetative, then a sensitive and ultimately a human, soul.  In Cardinal Schönborn’s Chance or Purpose? we quoted St Thomas’s answer to the question whether there could be more than one soul in man.  It is worthy of note that in giving the answer St Thomas did not suggest that one of these postulated later souls was a development of an earlier one.  This is consistent with his analysis that each soul—vegetative, sensitive, intellective—is specifically different.  Each establishes a different perfection.

Its soul is the substantial form of each living thing.  It is the reason, as St Thomas says quoting Aristotle, for the unity of the living thing.  Its soul is what makes the living thing to be, to live and to be one—all in the same act.

Now, let us complete the response.  The major premise of the argument is—“If earth could have the potency to become Adam…”  But it cannot!  There is no natural potency which would enable “earth” to become a man.  To think so is to follow the arguments of the materialists as, for instance, Dr Michael Denton in the Prologue to his Nature’s Destiny where he says—

“the cosmos is a seamless unity… in which all phenomena including life and evolution and the origin of man, are ultimately explicable in terms of natural processes.” [9]

“Earth” can become man only through obediential potency, a potency specified not from the act whereof it is receptive, but from the agent whereof this act is the effect.  And that, since it requires an agent with infinite power to bring it about, namely God, contradicts radically the whole of the materialist thesis.

There is another problem.  One might properly argue that something material derives from something material.  But when the writer seeks to use that as a premise to argue to the derivation of one form from another the argument fails.  Form is not to form as matter is to matter, for form (i.e., act) signifies perfection while matter signifies only what is perfectible.

Now, it might be objected that since nothing is impossible to God the implementation of Darwinian evolutionary theory cannot be absolutely excluded.  It is this, perhaps, that gives the theologians pause.  But the proposal serves no purpose, for God has already given us an explanation of how He created all natural things, and of how He brought them into existence.[10]   He did not go through a series of transient forms to produce His creatures.  He produced them all—each of them perfect—at once; together; in the moment of creation.  The principle of economy applies to deny the Darwinian thesis: Entities are not to be multiplied unnecessarily.

As an aside it should be noted that in his review of the book by American scientist and metaphysician, Anthony Rizzi, Science before Science[11] , Monsignor John McCarthy of the Roman Theological Forum, exposes a defect in the thinking of that author which is shared by many scientists, Catholics among them.  He remarks—

“Rizzi speculates that it is even likely that human technicians will some day be able to make ‘from scratch’ all of the ingredients of at least simple animal organisms, and that, when all of the material ingredients will be present and properly arranged, the organism will spring to life (p. 252, note 443).”[12]

Rizzi here confuses the physical with the metaphysical (and, indeed, the artificial with the natural).  “In living things,” Aristotle says, “to live is the same as to be.” [De Anima II, 37]  St Thomas adds this commentary:

“Here [Aristotle] uses two arguments: first, the cause of anything as its essence, i.e., form, is the same as the cause of its being, for everything has actual existence through its form.  Now it is the soul that gives being to living things; for their being is precisely their life which they have from the soul.  Hence the soul causes the body as its form…” [In II De Anima, lecture vii, 319]

The essential act of every natural thing, its form, is also its existential act.  The syllogism that follows on the philosophers’ reasoning is simple:

That which gives life to any thing is the same as that which gives it being:
But God alone is that which gives being to any thing;
Therefore, God alone is that which gives life to any (living) thing.

In other words, only God can create the soul of any living thing.[13]   In fairness to Cardinal Schönborn, it should be said that he sees this issue more clearly than Anthony Rizzi.

“In order for life to come into being on our planet, a whole series of preconditions were needed...  Yet these… were—and are—only the framework...  They do not constitute the creative cause of life.  They all play a part… yet the new element in the development of the world, which we call life, cannot be derived from them.  For it… truly needs the creative act of God, the ‘divine spark’...”  [Chance or Purpose? p. 82]


Michael Baker
10th November 2008—St Leo the Great


The Division of Act and Potency

Division of Act[14]

Act is either pure (act without any potency admixed, and therefore neither received in some potency, nor receptive of some further act), i.e., not together under some respect also a certain potency—and this is God.  Or it is non pure (act which is in some manner composed with potency).  If it is non pure, act is to be considered under two respects, 1) in the static order, the order of be; and 2) the dynamic order, the order of do.

Non pure act in the order of be is either:
   essential (or formal, or quidditative) act, and then it is either—
       a) substantial act which is either—
             i) unreceived but receptive (angelic essence); or
            ii) received and receptive (substantial form of material being); or
       b) accidental act, which is received and receptive (accident); or,
   existential (or entitative) act, which is be which is either—
       a) substantial act, i.e., be-in-self; or
       b) accidental act, which is be in and from some substance, i.e., be-in-other.

Non pure act in the order of do is either:
   metaphysical act, which is per se immanent and transcendental action, and is twofold, namely,
       a) know, or
       b) appetise; or it is—
   physical act, which is predicamental action, and then either—
       a) per accidens immanent, (or automotion) such as nutrition, growth etc.; or
       b) utterly transitive action (heteromotion), such as push, cut, corrode, burn, build, etc.

Division of Potency

As said above, potency is either passive or active.

Passive potency is twofold: it is either—
       a) pure, that is, potency which is not in any respect act and this is primary matter (which is actuated by substantial form and in combination with it constitutes a corporeal essence); or
       b) non pure, or mixed potency, which is together potency relative to something, and act relatively to something else (i.e., potency and act in diverse orders), and then, it may be considered as either—
             i) mixed potency taken relatively to some act, and then either—
                    a) potency for be or existence (entitative potency), which is either towards substantial be, or be-in-self (substantial essence), or towards accidental be, or be-in-other (accidental essence); or
                    b) potency towards accident or accidental form (which is the potency of a substance for accidents (accidental potency); or
            ii) mixed potency taken relatively to the power of another agent, and then, either—
                    a)  relative to the power of a natural agent—natural potency; or
                    b)  relative to the power of a superior agent—obediential potency.

Active potency (or power) is “the principle of change or of movement in another, inasmuch as it is another.” [Metaphysics V, c. 12, 1019a; In V Metaphysics, lect. 14, n. 955]  It signifies primarily, then, capacity for acting on another, but is extended to signify capacity of acting in any manner whatsoever, including the power to act immanently.  It is, then, either—
   Subjective power, a principle of action or of operation which is the power of a created agent whose operation (and not merely the effect thereof) is diverse from, and proceeds from the agent, and is either—
             i) power of acting vitally or automotively, which power is called “faculty” and this is either—
power of acting per se transitively but per accidens immanently as occurs, for example, in the power of nutrition; or,
            ii) power of acting per se immanently, and this is either—
                    A. power to know, cognoscitive power, or
                    B. power to appetise, appetitive power; or it is
           iii) power of acting heteromotively (non-vitally) which is called “force”; or,

   Non subjective power which is the power of the uncreated agent, God.

Non subjective power is a principle of an effect, but not of operation itself.  It is the Divine Power, for—

“in God is saved the notion of power as regards this, that it is the principle of an effect, but not as regards this, that it is the principle of the action which is the divine essence.” [Summa Theologiae I, q. 3, a. 3]

St Thomas clarifies this where he says:

“God is pure act, having nothing of potentiality.” [Ibid. I, q. 3, a. 2]


[1]   The material is drawn largely from the text of A. M. Woodbury S.M, Ph.D, S.T.D, [Regent of Sydney’s Aquinas Academy 1944-1974] entitled Ostensive Metaphysics, Treatise I Ontology.

[2]   This is a very sketchy (and inadequate) treatment of the doctrine of analogy.  St Thomas treats of it in a number of his works including the De Potentia, the De Veritate, his commentary on Aristotle’s Metaphysics and in Book I of the Contra Gentiles.

[3]   Summa Theologiae I, q. 5, a. 5, ad 3

[4]   Or, more precisely, that whereby something intrinsically is perfect under some respect.  If something is found to be imperfect, it must be so from a reason other than the act whereby it does be what it is, for imperfection and perfection are opposed contrarily and the Principle of Diverse Reason applies: Not the same is the reason of opposites.

[5]   From 1944 to 1975.  Within ten years the Academy’s governing body, the Australian Marist Order abandoned the teaching of the Church’s philosophy.  The Academy’s teachers faithful to St Thomas’s teaching then formed the Centre for Thomistic Studies.  Cf.

[6]   That primary matter must manifest itself in combination in the elements of secondary matter essential to life—calcium, carbon, oxygen, hydrogen, nitrogen, sodium, potassium, etc. and the molecules formed from them—as well as in the water in which they are contained (whether in suspension or solution), does not affect the validity of the principle.

[7]   Like act, potency, good and other simple notions, form is an analogous term.  When said of natural essences and of artificial ones, form signifies something same but also something unsame, as said above.

[8]   At first, perhaps, only inchoately; but inevitably.  His wife, Emma, could see where Darwin’s theorising was leading him as Dr Michael Denton shows in his Evolution a Theory in Crisis, London (Hutchinson), 1985, pp. 54-5.

[9]   Nature’s Destiny: How the Laws of Biology reveal Purpose in the Universe, The Free Press, New York, 1998, pp. xvii-xviii.  Cf. our review of the book:

[10]   St Thomas’s teaching that much  of what Almighty God created “in the beginning” was created in potency is not to be dismissed on the basis that these elements of creation were given only a mental,  or merely formal, existence.  A fertilised seed may lie in the ground for twenty years before meteorological conditions precipitate its shooting and development.  Yet the plant is really present in the soil in potency.

[11]    The Science before Science, Baton Rouge, IAP Press, 2004.

[12]   Anthony Rizzi’s The Science before Science

[13]   In a world bereft of metaphysics, it is not understood that there are some things that even God cannot do.  He cannot create a square circle, because the postulated thing is intrinsically impossible.  Nor, for a similar reason, can He give to any creature—even the highest of the angels—the power to create because this requires infinite power, and only God possesses it.

[14]   The material sidelined is technical and requires the reader’s careful consideration.  It is not essential to the argument but included for the sake of its completeness.