Aquinas's Little Known Way to God
Aquinas's Little Known Way to God
Notes on "The Argument From Existence"
Principle of causality: Whatever is reduced from potential to actual is actualized by something already actual. Alternatively: Contingent beings demand a cause distinct from themselves.
Summary:
At least some things exist but not in virtue of what they are -- we call them, contingent. But no contingent being can exist unless there exists that which exists in virtue of itself -- and that we call, necessary. So, there is at least one necessary being, something which exists, not just in itself, but through itself and in virtue of what it is.
However, for a being to exist in virtue of what it is, is for that being to be pure actual existence itself, and there can only be one such reality, because pure actual existence is not susceptible to multiplication (features of differentiation). So, there is just one being which is pure actual existence itself -- namely, God -- which is the ultimate cause of everything else that exists.
Procedure:
Aquinas’s argument for God found in the De Ente et Essentia is a causal argument concerning the property of existence.
There are three hurdles to be cleared before launching into Aquinas’s argument for God. We must discuss causality, causal series, and existence. Thus, we’ll briefly discuss causality and whether existence is a property susceptible to causal reasoning.
In short: IF we can argue that causality is real feature of the world and IF we can argue there are types of causal series that cannot regress infinitely (which must include a primary member: a “first cause”, though not necessarily temporally first) and IF we can argue that existence is a causal property susceptible to such a causal series, THEN we’ll be able to arrive at some fundamental, uncaused cause of the existence of things that just is subsistent existence itself -- namely, God.
Causality
Cause: that which contributes positively to the being of another.
Further, causation is a matter of dependency relation. Which is to say, whatever is the effect depends on -- or in some sense, derives from -- the cause(s).
As Elizabeth Anscombe puts it, “... causality consists in the derivativeness of an effect from its causes. This is the core, the common feature, of causality in its various kinds. Effects derive from, arise out of, come of, their causes. For example, everyone will grant that physical parenthood is a causal relation. Here the derivation is material, by fission. Now analysis in terms of necessity or universality does not tell us of this derivedness of the effect; rather it forgets about that. For the necessity will be that of laws of nature; through it we shall be able to derive knowledge of the effect from knowledge of the cause, or vice versa, but that does not show us the cause as source of the effect. Causation, then, is not to be identified with necessitation. If A comes from B, this does not imply that every A-like thing comes from some B-like thing or set-up or that every B-like thing or set-up has an A-like thing coming from it; or that given B, A had to come from it, or that given A, there had to be B for it to come from. Any of these may be true, but if any is, that will be an additional fact, not comprised in A’s coming from B. If we take ‘coming from’ in the sense of travel, this is perfectly evident.”
As noted, effects are not demanded by their cause(s). They are only dependent upon them and rendered intelligible by them. This is clearly the case when it comes to agent causation and libertarian freedom - the ability to choose (x) or not-(x) based on reasons. Plausibly, it is true of phenomena in quantum mechanics, as well, statistical explanations, and so on.
Of course, this assumes we are talking about causes as substances capable of producing effects (that is, as potential cause versus actually causing cause). But inasmuch as an effect is already produced the effect is demanded by the cause -- this is true, but trivial. Obviously, if something is generated it cannot (in the same aspect) be not-generated. However, this is not to say it couldn’t have been otherwise prior (either logically or temporally) to generation.
Example: If I choose to pick up the apple and am picking up the apple, then my ACTING as cause is SIMULTANEOUS with the effect I am producing (my picking up the apple is the same thing as the apple being picked up, seen from differing perspectives), and so the effect is necessitated because there can be no effect without the cause (even if we can “imagine” the effect without imagining the cause). But again, that does not mean prior to my judgment I was necessitated to pick up the apple. I could have picked up a papple (hybrid of apple and pear).
Example 1: The pot is hot because the fire heated it. The causal property of heat has been derived from (and is dependent upon) that which possessed that causal property essentially -- namely, fire -- being in contact with it. Had the fire not come into contact with the pot, the pot would not have been heated, less something else with that causal property had been there to pass it along.
Example 2: I chose to give my wife flowers instead of candy because I favored the reason that flowers last longer over the reason that candy tastes good (because my will has the power to make some finite motivate efficacious!) I could have given my wife candy (all antecedent conditions remaining the same) but freely decided not to. The effect of my wife getting flowers is dependent upon, and rendered intelligible by me, the cause, favoring a reason, though I could have done otherwise. The effect is still dependent upon the cause in this case even if not demanded by it (in this case, demanded by my existence as potential cause).
Causation also involves the actualization of potential - the realization of some possibility of being - by something that is already actual, something already realized, existing, and capable of producing an effect.
This analysis of causation, which underlies the causal principle “whatever is reduced from potency to act is actualized by something already actual” is necessarily true, since 1) from nothing, nothing comes, and 2) potential being qua potential has no actual causal power, otherwise it would not be potential but actual. Think: My potentially writing this article does nothing to teach anybody Aquinas’s De Ente Argument until the article is actually written. Thus, no potential can be responsible for something actual. Therefore, only that which already actually is (in some sense) could bring about some possible reality.
Note: this causal principle is not affirmed inductively by collecting a sufficient number of examples but deductively by disproving two of the three (logically exhaustive) candidates as metaphysical impossibilities and ensuring the third. In other words, we do not conclude that “whatever is reduced from potency to act is actualized by something already actual” because we see some extensive number of examples of this in experience (though we do) and no clear counter examples (also true), rather we see that among the three conceptual alternatives (actual being, potential being, and nothing) only one is metaphysically tenable for producing an effect. Because we can be certain that nothing comes from nothing and that potential qua potential has no actual causal ability, the ONLY LOGICALLY POSSIBLE option is that something comes from something that already, actually is. This is a critical consideration, because this notion of causality is sufficiently general that it holds for any possible reality, any possible universe. It cannot be otherwise.
Regarding the Humean suggestion that because we can conceive of something coming from nothing, therefore the principle of causality is undermined, a brief response borrowing from Ed Feser is in order: To wit, to conceive of an effect without simultaneously conceiving of its cause does nothing to show that it is metaphysically possible for an effect to exist without a cause, anymore than conceiving of a man without simultaneously conceiving of his height does anything to show it is metaphysically possible for a man to exist without having a height — obviously, that is not metaphysically possible. Thus, the move from conceivability to metaphysical possibility is not just question begging, but false.
Additionally, Gyula Kilma has this to say regarding the necessary relation between cause and effect: “... since the agent is a thing that has an active power (an ability to act), on account of which it is capable of bringing into actuality something, the patient, in some respect, namely, in that respect in which it is in potency to become actual, the action of the agent and the actualization of the patient are the same process; as Aquinas put it: ‘… action and passion are not two motions, but they are one and the same motion: for insofar as it is from the agent, it is said to be action, and insofar as it is in the patient, it is said to be passion.’ But then, if the act of the agent as such and the act of the patient as such are one and the same in reality, but distinct only as to how they are conceived, then the one cannot be without the other in reality, even if the one can be conceived without it being conceived as the other: for one and the same thing cannot be there and not be there, no matter how it is conceived; therefore, the act of the per se cause cannot be there without the act of the per se effect, that is to say, the per se effect of a per se cause has to be there as long as the agent is acting and the patient is receiving its action, for the action and the reception are one and the same process of actualization inherent in the patient, coming from the agent.”
Regarding self-causation, we can rule this suggestion out as necessarily false because it would entail that something had to pre-exist itself to cause itself, which is absurd, but also that something would have to both actual (causing) and potential (caused) in the same aspect, which is an explicit contradiction.
Regarding circular causation (A causing B causing A, etc), we can rule this suggestion out as necessarily false, as well, because in a circular arrangement A would be the per se efficient cause of itself (we will cover per se vs accidental causes shortly), no matter how many intermediaries, and because causation is always irreflexive and transitive, a cause can never be related to itself as cause, and circular causation directly contradicts that.
Regarding the objection that quantum mechanics undermines the principles of causality, because it shows things (particles) can begin without a cause, here a brief reply may also be given. For it is untrue that quantum mechanics shows that things can exist without a cause; rather, quantum mechanics (at most) shows that effects are not demanded or necessitated by their underlying cause(s), which is consistent with the causal principle, or simply that the underlying cause might not be obvious, which is also consistent with the causal principle. In the case of certain particles spontaneously emerging, this takes place, as some physicists propose, because of underlying energy states. In short, it is a misunderstanding to say they emerge from nothing because they emerge spontaneously. Spontaneous causation is not something coming from nothing.
Also regarding quantum mechanics, Rob Koons argues the following: “A common objection to any PGC (principle of general causation) appeals to the apparently indeterministic character of the laws of quantum mechanics (in particular, the indeterministic character of wave collapse). Quantum mechanics could be taken as providing empirical evidence that exceptions to any PGC are in fact widespread throughout the physical world. However, this objection confuses being caused with being determined. What quantum mechanics suggests is that indeterministic or probabilistic causation is widespread. When an undetermined quantum result is observed, the result is not uncaused: it was caused by the pre-existing quantum system that had the non-zero objective probability of resolving itself into the observed outcome.”
Furthermore, to deny the causal principle is to deny the principle of sufficient reason, which, as I’ve argued elsewhere, entails a radical, self-defeating skepticism. In short, if things can happen uncaused (and for no intelligible reason whatsoever), then why couldn’t our thoughts happen uncaused (and for no intelligible reason whatsoever)? But if that is the case, then why should we trust any of our thoughts, including the thought that things and events can happen uncaused? There is no escape: the causal principle that “whatever is reduced from potential to actual is actualized by something already actual” is always and everywhere true.
Conclusion: Causation is a real, undeniable feature of the world which involves the actualization of potential being by already actual being. In short, a cause is whatever contributes positively to the being of another.
Causal Series and Infinite Regress
Moving on. There are two types of causal series to consider, one of which (per se, or essentially ordered causal series) factors significantly into Aquinas’s argument for God. They are:
Per Se (or essentially ordered) causal series.
Where the causal property in question is not possessed inherently by subsequent members of the causal series.
Thus, a causal series (x) → (y) → (z) is essentially ordered if when causing (z), (y) borrows from (x) the power to do so.
THUS, in a per se causal series some cause is the cause OF THE CAUSALITY of the series.
For example: the moon reflects light from the sun and so “the moon shining” is something which the moon depends upon the sun to achieve. Thus, if the moon illumines my bedroom, the moon borrows the power of illumination from the sun in doing so. Because while the moon may have the inherent ability to reflect light, the moon does not have the inherent ability to produce light. Thus, the moon does not shine in virtue of what it is, but in virtue of something else -- in this case, the sun.
Furthermore, if the sun ceased to exist the light would “drop out” of the causal series which means the moon (and subsequently the bedroom) would cease to shine, because the sun in this case is the cause OF THE CAUSALITY of the series, with the causality being illumination.
Notice it would not matter how many moons there are reflecting light from one another. Without something which has the ability to produce light in virtue of what it is (i.e. the sun) there would be no light in the causal series to begin with. So, even if there were an infinite number of moons, there would still have to be at least one sun (or some other inherent light source) either within or beyond the series to explain why any moon is reflecting light instead of not.
Consequence: In a per se causal series, because the causal property is derivative or “being borrowed” by subsequent members there must be a primary member or that which has the causal property in virtue of what it is, otherwise the causal property would not enter the series to begin with. Otherwise we would have a collection of passive receivers (receivers and reflectors of light, in the case of moons) but with nothing to receive (no giver/producer of light, and therefore nothing to receive or reflect).
Put differently, in a per se causal series, there cannot be an infinite regress of intermediary causes precisely because the intermediary causes of the series are mere instruments, and without something powering those instruments the instruments would be useless -- i.e. causally inert. To borrow an analogy from Feser, a paintbrush with an infinitely long handle cannot answer why the paint brush is moving, because the handle is but an instrument connecting a person's hand to the brush itself with no inherent power of movement. Extending the handle indefinitely only indefinitely delays (but does not provide) the intelligible explanation for the movement of the paintbrush, which must come from something (i.e. a person, or machine) that has the power of movement in virtue of what it is. Same with the analogy above regarding the sun and the moon. No matter how many moons we add to the causal series (or how we arrange them), we cannot explain why light exists in the series at all just by multiplying the number of moons. Thus, appeals to an infinite regress have no force against the need of per see causal series to have a primary member.
Another way to think about it: If (w) is dependent upon (x), and (y) is dependent upon (z), and (z) is dependent upon (a), and so on and so forth, ad infinitum, the conditions for (w) to exist will never (and could never) be fulfilled, because there is always 1+ more condition we could go in an infinite series, meaning the ultimate fulfilment of conditions needed for (w) to exist can never be reached.
Thus, (w) remains forever conditional, always “iffy,” but never actual. Dependent upon, dependent upon, dependent upon, etc, etc…
See the problem? It is one of construction. Just as you could never add white tiles to the point of building a purple floor, nor could you add dependent realities to the point of creating an independent reality, nor passive receivers (of some property) to the point of getting a generator (of that same property).
But notice this. The whole of reality is independent in terms of existence, because beyond “the whole of reality,” there is (by definition) nothing. And so, nothing could cause “the whole of reality,” which means not *everything* can be a caused reality, otherwise the whole of reality (even collectively) would be dependent upon something beyond itself in order to exist -- i.e. In need of a cause -- making it impossible to exist, because there could never be a cause beyond the whole of reality. But reality exists -- it is here. So, there must be something foundational, standing independently. Not everything can be caused; not everything can be dependent. In short, positing an infinite regress of caused, dependent things does nothing to escape the conclusion that there must be at least one uncaused, independent reality to explain why anything dependent exists instead of not.
The critical consideration is that in a per se causal series, the causality of the series is DEPENDENT (though not necessarily instantaneous) upon the action of some primary cause. Should the primary cause not exist, the causality of the series itself would not exist. If the sun weren’t emitting photons, the moon would never have begun to shine.
Accidental causal series.
Where the causal property in question is possessed inherently by subsequent members of the causal series.
Thus, a causal series (x) → (y) → (z) is accidentally ordered if when causing (z), (y) does not borrow from (x) the power to do so.
Example: If Bob begs Harry and Harry begets Frank, Bob’s ongoing existence is not necessary for the begetting of Frank by Harry, because once Harry is born (and develops to a certain age) Harry has the power intrinsic to himself to produce a son, and does not borrow or derive that power from his father Bob. Of course, Harry could not beget Frank if he were not first begotten by Bob, but Bob’s concurrent existence is no longer needed to explain the begetting of Frank after Harry is already begotten. Hence the causal series described above is accidentally, rather than essentially, ordered.
The critical consideration for an accidental causal series is that since the casual property (or ability to produce the causal property) in question is possessed inherently by each of the members of the series, such a series does not demand a primary member (because we can explain the causality by the immediately preceding member), and so, in theory, could regress to infinity.
Keep these causal series in mind because they will become relevant later in Aquinas’s argumentation for God, since Aquinas’s claim is that his arguments involve a per se causal relationship, and, that being the case, must include a primary member.
Finally, notice that “primary member” does not mean “first member” in the sense of temporal ordering, such as someone who flicks the first domino. While it MAY be the case that the primary member is first in the temporal sense, it does not have to be so. “Primary member” means only that which possesses the causal property in virtue of what it is and has the ability to pass that property along to other members in the series. This is important because even if some causal series doesn’t have a “first member” (goes on infinitely, for example) that would not mean it doesn’t have a primary cause. For example: even if the universe were eternal, that wouldn’t mean the universe doesn’t have a cause if 1) contingent existence is something which demands a causal explanation and 2) the universe (which is contingent) doesn’t explain its own existence. If there were a per se causal series extending infinitely that would just mean a primary cause is required beyond that series to explain why it exists instead of nothing.
Having considered the nature of causality and differences between causal series, we can now turn our attention toward existence to ask whether the existence of things might itself pertain to causal reasoning which traces back to a primary member.
Existence
First, we should consider whether a thing’s existence is a property similar (in however loose a sense) to other properties we ascribe to it. If so, then we can talk meaningfully about something’s existence as a property that is potentially caused (assuming that something doesn’t possess existence inherently) and begin a causal hunt for something responsible for actualizing the existence of things.
Certain analytic philosophers -- following Frege, Russell and Quine -- deny that existence is a first-order predicate and instead think of existence as a “property of concepts,” or that which is expressed by the existential quantifier, translated to mean “there is an (x) such that (x) if an (f)” which says there is some property (for example: “being a tiger”) that has been instantiated. In other words, to say that tigers exist is just to say, “there is at least one (x) such that (x) is a tiger.”
The problem with the “Frege-Russel-Quine” view of existence is that to make sense of property instantiation we must presuppose existence, since no property can be instantiated without some individual already existing. And whatever presupposes existence cannot explain it.
Turner Nevitt critiques the Frege-Russell-Quine position as follows, “Take the statement. ‘Planets exist,’ and now consider Vulcan (the mistakenly posited inter-Mercurial planet). Does Vulcan instantiate the property of being a planet? If so, then the analysis of existence in terms of property instantiation is mistaken, since Vulcan does not in fact exist, so its instantiating the property of being a planet does not show that planets exist. But if Vulcan does not instantiate the property of being a planet, of course that can only be because it does not in fact exist, which shows that existence is presupposed by property instantiation, rather than being explained by it.”
Feser (again in Five Proofs) offers his own critique in arguing, “There is, in any event, ample reason to doubt that the notion of ‘specific existence’ captures everything that needs to be captured by an analysis of existence. Consider that when we are told that ‘cats exist’ means that ‘there is at least one x such that x is a cat’ or that something falls under the concept of being a cat, there is still the question of what makes this the case, of what it is exactly in virtue of which there is something falling under this concept. And the answer to this further question is, as Knasas and others have pointed out, what the Thomist is getting at when he argues that the existence of a thing is distinct from its essence (in this case, from the essence of a cat), and must be imparted to it, so as to actualize what is otherwise merely potential, if that thing is to be real.”
So, the existence of any individual object is indeed a property, however unique. Regardless, the existence of any individual thing stands in need of explanation. Why is it?
Thus, when considering existence, we can meaningfully ask what accounts for the existence of any individual thing. Do things exist in virtue of what they are, or do they derive existence from something beyond themselves?
For example: My ability to laugh flows from my being a rational animal, even if some external factor (say, a clown) is used to activate it, sometimes. Whereas my being “warmed by the sun” is a property I possess derivatively, borrowed from the sun’s rays shining upon my pale physique. I do not make myself warmed by the sun (though I can make myself laugh); the sun does.
So, which is existence? Is existence something things possess in virtue of what they are, or is existence something imparted to them?
Aquinas is prepared to answer that in the case of everything except God, all contingent, qualitatively finite beings derive their existence from God for every moment they exist.
The Real Distinction
To see why Aquinas thinks the contingent existence of finite things traces back to the self-existence of a “uniquely unique” and qualitatively infinite being (i.e. God), we must consider his arguments for the real distinction between the essence and existence of any finite thing.
As stated, Aquinas holds for anything other than God there is a real distinction between the essence (or “what-ness”) of a thing and its esse or act of existence (the “is-ness”).
A real distinction is one that holds independently of how we think or talk about something: it is, in other words, not merely a verbal distinction (bachelor vs unmarried man) nor mental distinction (the glass being half full vs half empty), but a distinction that attains in things themselves.
A real distinction, however, does not entail separability. As David Oderberg explains, the circumference and radius of a circle are really distinct (as proved mathematically) though you could never have one without the other in concrete reality.
Once the real distinction has been established, we must, then, according to Aquinas’s causal reasoning, trace back to that in which there is no distinction between essence and existence -- back to that which exists in virtue of what it is; i.e. pure actual existence itself (God!) - to explain why any contingent thing exists and not nothing instead. And that Aquinas will argue is God.
Arguments for Real Distinction
Argument 1 for the Real Distinction: Knowing essence without existence.
Suppose you describe to an extremely sheltered person the essences of a lion, pterodactyl, and unicorn. Assuming this person has never lived outside a cave, they would not be able to tell you -- from a mere essential description of each creature -- which currently exists, which previously existed but has gone extinct, and which has never existed.
This suggests that we can know the essence of a thing without knowing whether that something exists, hence support for there being a real distinction between the essence of any finite, particular thing and its actual existence -- otherwise to grasp the essence of a thing would be to grasp its existence, which is not the case. To know the latter we must venture out and have a look.
Objection: But does this not beg the question that we have a complete understanding of a thing’s essence? Perhaps the reason we do not know whether something exists is because we don’t know everything there is to know about its essence? Reply: Here, two responses are in order, borrowing from David Oderberg and Edward Feser. First, notice this. To say of a lion that it is a reptile is to misconceive what a lion is. But to say that no lions exist is to get something factually wrong, but not essentially wrong (for lions COULD go extinct) and therefore not to misconceive what a lion is. What this suggests is that even if we knew all there is about a lion down to the last essential detail, we would know a lion is not a reptile, but we would not know whether a lion exists. Thus, having an incomplete grasp of something’s essence -- which is the case for many if not most things of our experience -- does not mean we don’t know enough to see there is a real distinction between the essence of a thing and its existence -- otherwise to say lions do not exist WOULD be to misconceive the essence of what it is to be a lion, and that is not the case. Furthermore, once we know that a lion is not a reptile, we will know that about any lion that has existed, currently exists, or could exist in the future. However, even if we know some lion currently exists, we do not know whether lions have always existed or will exist always. Why? Simply because there is a real distinction between essence and existence among qualitatively finite things.
Objection: If essence and existence were really distinct, then we should be able to have them occur separately, which is never the case. So they must not be really distinct. Reply: Gyula Klima shows what is wrong with this objection in saying, “... this assumption is obviously false: for it is clearly possible to have distinct, yet necessarily co-occurring items in reality. For example, it is clear that the triangularity of any particular triangle (its having three angles) is not the same as its trilaterality (its having three sides), unless sides and angles are the same items. But it is also clear that one cannot have a particular triangularity without a particular trilaterality. So, we have two really distinct items here, which are nevertheless inseparable in reality.”
Finally -- and this is somewhat of a secondary point -- but to know what a thing is, is different from knowing how a thing is. We can know that something is gold without knowing it’s melting temperature (an inseparable accident) and we can know that a metal before us is melting without knowing that that metal is gold. Thus we should not think that to not know everything about a thing -- including all its proper accidents -- means we do not know what something is.
Argument 2 for the Real Distinction: The contingency of things.
The most obvious affirmation of things not existing in virtue of what they are is our regular experience of their arrival and departure from reality. Things come into existence -- lions, particles, Whitesnake albums -- and pass from it. But if something existed in virtue of what it is, then it would exist necessarily, and could never come in, nor depart, from reality. It would simply and always BE.
In other words, if something exists in virtue of what it is and does not receive existence from another, then it could never not be, it could never fail to exist. But things of our experience are radically contingent and fail to exist all the time. So, there must be a real distinction between what those things are and their act of existence.
Objection: Why say contingent things have a real distinction between essence and existence, rather than merely having a cause and/or potential for non existence? Reply: Clearly, if something existed in virtue of what it is, it would thereby not have a potential for non-existence and would also be incapable of having a cause, because there would be no point at which it did not exist. The objection misses the point.
Argument 3 for the Real Distinction: The multiplicity of being.
Aquinas begins with a hypothetical that if -- if, if, if -- something existed in virtue of what it is (whose essence and existence were identical), that something must be pure actual existence, existing through itself. Or pure actual existence, for short.
Why so? Because if there were any part, feature, aspect, factor, dimension, etc, of this reality that were NOT an act of existence existing through itself, then that part, feature, aspect, factor, dimension, etc, would (by definition!) NOT BE an act of existence, existing through itself, and so would HAVE to be caused. After all, if something doesn’t exist through itself, it exists through another.
This entails that whatever else this hypothetical necessary being is, it must be a pure act of existence, existing through itself, which is susceptible to no differentiating features.
But for something to be susceptible to multiplication is for something to be susceptible to differentiating features (that is, some way of telling one instance apart from another instance). But since pure actual existence, existing through itself is not susceptible to any differentiating features, it is not susceptible to multiplication. Therefore, it can be one and only one. If such a being exists, it would not just be unique, but uniquely unique.
Restated: Whatever else this hypothetical reality is (whose essence just is existence itself), it must be a pure act of existence existing through itself, and, because of that, uniquely unique. Why so?
First, if this hypothetical reality -- i.e. a reality which exists in virtue of itself, whose essence is just is existence itself -- were not active (or actual), then it would need to be activated (caused), which makes no sense, because then it would NOT exist in virtue of what it is, but in virtue of something else, which is contradictory. Upon this realization, we can deduce something else: that the hypothetical reality must be a pure (read: uncomposed, absolutely simple) act of existence, existing through itself. The argument is as follows:
If this hypothetical reality were not a pure act of existence existing through itself, then there would be a part (or dimension, feature, aspect, etc.) within this hypothetical reality that was different from the act of existing through itself.
But if there were a part (feature, aspect, etc.) within this hypothetical reality that was different from the act of existing through itself, that part or dimension would then be caused in its existence, because it would either NOT be actual or NOT be existing through itself. But then we’d have an uncaused-caused (or independent-dependent) reality, which is contradictory.
So, this hypothetical reality must be a pure act of existence existing through itself. It is not only utterly unique, but uniquely unique -- there could not, in principle, be more than one reality that exists in virtue of what it is, whose essence is identical to existence.
Conclusion: This leads us to conclude that for any reality where there is, or could be, more than one instance -- dogs, particles, stalks of corn (i.e. any qualitatively finite reality) -- they are not that which exists in virtue of what it is, but that which exists in virtue of something else. They are metaphysically composed realities: a limited essence that is imparted with an act of existence from something beyond itself. They are, in a word, caused realities, standing in need of external explanation.
Aquinas’s Little Known Way to God: Putting It All Together
Acknowledging the real distinction between essence and existence among qualitatively finite things sets in place the final piece needed to engage a sequence of per se causal reasoning, since the causal property in question (existence) is not possessed inherently by the subjects under investigation -- that is, by any finite, limited being. Rather, all qualitatively finite instances of being receive or borrow existence from something beyond themselves, and because they do not possess existence in virtue of what they are, they must derive existence at all times throughout their being present in reality. They are thoroughly and ongoingly caused to exist, not just when they began to exist (if they began to exist; some may be eternal) but as they continue to exist. In other words, they are not only brought into existence, but held in existence, by something beyond themselves. We should want to know: What is that thing?
Since we have already argued that a per se series of causes must involve a primary member -- i.e. that which possesses the causal property of the series in virtue of what it is, and thereby has the power to pass that causal property along to other members in the series -- we can engage per se causal reasoning as follows. Because certain things exist, but only in a derivative or participatory fashion, there must be a primary member in any causal series involving the existence of things which do not account for their being actively present in reality in virtue of what they are. There must, in other words, be that which exists in virtue of itself and, therefore, whose essence just is existence itself. Otherwise no contingent thing would exist.
What we have done at this stage is simply to show that the previously assumed hypothetical reality -- that is, a reality which exists in virtue of itself and which must be the pure act of existence, existing through itself -- is demonstrably actual. Such a reality is required -- in fact, demanded by the causal reasoning -- to explain why anything exists instead of nothing upon experiencing a world suffused with contingent realities whose essence is really distinct from their act of existence: things which exist, but need not exist, and so require an extrinsic explanation for their inclusion into reality. That explanation can be found only in that which exists in virtue of itself, whose essence just is existence itself, is uniquely unique, and transcends any qualitative limitation or restriction on being.
At this point, more needs to be done to show why this being whose essence just is existence is to be identified with God (as traditionally understood), but we can briefly examine a few reasons why Aquinas believes this to be the case. For one thing, this entity is the ultimate cause of everything else which exists, and surely if God is anything, God is that. Next, this entity exists in a purely and fully actual way -- it can impart existence to any logically possible reality, yet receives existence from nothing beyond itself -- which is textbook omnipotence. Further, because this being transcends all bounds and limitations on being (because all finite being is participatory being in their act of existence) this being must be trans-spatial and trans-physical -- that is, beyond the material universe. Furthermore:
1) it is not susceptible to multiplication through differentiating features (meaning it is uniquely unique and therefore one);1
2) is ontologically simple since parts require differentiating features which the unconditioned reality does not have;
3) is necessary because it cannot be caused nor destroyed and just is pure existence itself;
4) is immutable because it is purely actual and has no potentials to be actualized (and change requires actualization of potential);2
5) is perfectly good for the same reason, since goodness is the actualization of some potential relevant to (namely, that which fulfills) the natural perfection of a thing;3
6) Is immaterial and eternal because all material and time-bound realities have potential (to be here vs there, earlier vs later, older vs younger, etc.);
6) is omniscient since whatever is in the effect must in some way be found in its total cause and because the ultimate cause of everything else which exists is immaterial it must contain the essences of what it causes eminently in the form of knowledge -- that is, in an intellectual way;4
7) and is unconditionally loving since it grants the most fundamental good -- which is the good of existence -- to everything without those things having done anything to merit it.
Another way to support the non-compositeness of God is this: Complexity entails parts (true by definition). But the unconditioned reality is a pure act of existence existing through itself — that is, comprised of no parts whatsoever, for reasons already provided. Therefore, the unconditioned reality is non-composite and utterly simple. Furthermore, since parts entail limitation/restriction (the parts must be somewhere the whole is not, and/or do something the whole does not, etc.) the unconditioned reality must be inherently unlimited/unrestricted. No parts = no restriction = absolute simplicity and power.
Change being the actualization of potential. For a defense, see Ed Feser, Scholastic Metaphysics: A Contemporary Introduction (Neunkirchen-Seelscheid, Germany: Editiones Scholasticae, 2014), 31-36.
Example: I have the potential for more knowledge and it is good to the extent I actualize that given I have a rational nature. Knowledge perfects me. For a full defense see, David Oderberg, The Metaphysics of Good and Evil, (Abindgon, UK: Routledge, 2020), Part I: A Theory of Good as Fulfilment, Kindle.
To deny this is to suggest something can come from nothing, which is absurd.