How Metaphysical Certitudes Anchor Proofs for God

This brief essay is not intended to be a complete presentation of the classical proofs for God’s existence as proposed by St. Thomas Aquinas and his disciples. Even partially full treatment of these arguments would require book-length analysis.1 Many eminent Thomists — both classical and contemporary — offer comprehensive presentations.2

Rather, I note that many contemporary skeptics and atheists attack such proofs by rejecting the basic metaphysical principles from which they proceed. Thus, my present purpose is simply to defend our ability to know those basic principles with perfect certitude. Also, I will show how the mind can legitimately use such principles transcendentally, so as to prove God’s reality and know something of his nature.

Two Perfect Certitudes

There are at least two fundamental truths that appear so evident that no one really doubts them, or, at least, they are bound to accept them in their minds as absolutely true, even if they defend statements that appear to contradict them. They are: (1) that being cannot both be and not be from the same perspective and (2) that from absolute non-being nothing comes to be by itself. Some may wish to add other primary certitudes, but these are ones that most all human beings seem unable to deny in practice when correctly understood.

Of course, the principle of non-contradiction can be given intellectual defense.3 But my point here is that everyone really must employ this principle in practice. Even analytic philosophers who claim that existence is not a predicate find themselves unable to think of reality in terms other than that of being and non-being — dichotomously opposed. They may claim that it is merely a logical proposition to say that the same predicate cannot be affirmed and denied of the same subject. Still, their own minds, like those of the rest of us, are unable to avoid thinking of all things in terms of either being or non-being. Even trying to reduce truth to mere probabilities entails affirming decisively that something is merely probable and/or just how much it is probable.

The logical realm in which the analytic philosopher dwells is restricted to the conceptual order. If one reduces the concept of being to merely the conceptual order, the full implications of being will be missed. But, we do not first encounter being in a concept or as a pure abstraction. Rather, we encounter being in lived experience. As the eminent Thomist, Jacques Maritain, puts it, the first thing we know is being: Scio aliquid esse. I know something to exist.4

In affirming something to be or to exist, I encounter being first, not as a mere concept, but in a judgment of being — an affirmation of real existence, either intramental or extramental in nature. It is critical to note that this encounter, this lived experience, is the first thing that anyone knows or can know. This means that all further analysis is secondary to and presupposes what is given in this primary experience. That is to say, you cannot, in fact, come up with a secondary theory which somehow comes back and judges or counters this initial experience. All valid knowledge is built from and must be interpreted in terms of this absolute and undoubtable starting point.

Why Doubt Is Impossible

Why do I say that this affirmation of being directly encountered in lived experience is undoubtable? One has to think first of what it means to doubt. To doubt requires that it be possible to be wrong about something. But, to be wrong about something, there has to be a difference between what one thinks or says and what exists in reality. For example, I can doubt whether my car is in my garage, since I am here in my house and the car is not in front of me, even though I am certain that I parked it in my garage. That is, since there is a distinction between reality as I know it and reality in itself, it is possible that I am wrong. Thus, there is basis to doubt the truth of my belief.

Still, in my direct experience of something in any act of knowing, there cannot be any ontological or physical separation between the act of knowing and its own content. That is, the act of knowing itself is a union with something known. Were it not, I would simply not be conscious of anything at all. The act of knowing is a union having two distinct aspects or terms, which we call (1) the knower and (2) the object known. Were these distinct aspects of the act of knowing entirely separated realities, nothing would be known at all, since the union of knower and known would not exist.

That is why, in the immediate act of lived experience, we cannot actually doubt that we are having an experience, or knowledge, of something real.

As noted earlier, we may not know whether what we know is intramental or extramental. That does not matter to the reality as such of what is known. It only matters as to the state of being or mode of existence that the object known may have. That is, what is known may be a real extramental object or it may merely be an image, a fantasy, a concept of something, or a purely subjective experience with no external corollary. Such distinctions are irrelevant, since whatever is encountered is real in its own order. As such, it has some form of existence or reality which we call by the term, “being.” In affirming the reality of what I experience, I am making what is called a judgment of being.

This is not a mere concept of being, since a concept may refer to that which is or is not. Yet, even a concept, recognized as such, is a being in its own conceptual order. That is, even a concept of a unicorn, when known, is real as a concept. Thus, it presents itself as a being – the being of a concept existing in a mind.

From this judgment of something existing in some manner, we then abstract the concept of being. But being as conceptualized is not identical to the fullness of being as known in the lived experience, since the content of the experience itself is real, whereas the concept of being as a concept is recognized as, perhaps, not referring to anything real beyond itself at all. Curiously, I can still recognize the reality of the concept of being itself, which then has actual existence in its own conceptual order!

This is how the mind first comes to know being with certitude and why it knows, in the same act, that being is not non-being. The mind grasps the very nature of being and knows that it is able to do so in the very act of doing it. That is why we are all so perfectly certain that being is and cannot be non-being.

This is not merely some logical “rule,” but the most basic law of being or reality itself. No one can honestly doubt this while being aware of his actual experience of anything as existing. Even some hypothetical distant astral object about which we think we know nothing at all is subject to this instinctively metaphysical certitude. For, we are certain that either that possible object exists or it does not – and that, if it does exist, it cannot both exist and not exist simultaneously from the same perspective.

All this is merely a somewhat lengthy way of discovering that the mind is naturally comported with being itself in such manner as to know being and one of its most fundamental principles: the metaphysical principle of non-contradiction. This truth it grasps with perfect certitude – a truth which even the rankest skeptic cannot help but implicitly assume in his every judgment.

Still, some skeptics argue that the principle does not hold good at the submicroscopic level – offering experiment-based claims of submicroscopic actual contradictions using examples such as wave-particle duality. What they fail to notice is that their own submicroscopic observations would themselves by meaningless unless they assume that what is observed is what it is and not something else.

That is also why all ordinary human beings — even little children — know with certitude that something either is or is not and cannot both be and not be. The mind knows being by its very nature. Should it not do so, then nothing could ever be known for sure. In fact, nothing could be known at all – since reality could always be other than what we know.

The Second Perfect Certitude

In addition to the fact that things cannot contradict themselves, everyone knows with absolute certitude that you cannot get something from absolutely nothing. This truth is simply an application of the principle of sufficient reason. Unlike sufficient reason, this subset principle is evident even to those who might otherwise attack sufficient reason itself.

Some argue that you can get something from nothing, when the “nothing” in question is a quantum vacuum. This misconception is readily corrected once one understands that a quantum vacuum is not the “absolute nothing” which the philosopher is talking about. Rather, a quantum vacuum is simply the lowest possible energy state found in physical reality. It may be “almost nothing,” but it is still really something!

Again, even little children know that, if the magician’s hat is really empty, there is no way to get a rabbit out of it. In metaphysical terms, what is totally lacking in being cannot be a sufficient reason for anything, including rabbits.

The principle of sufficient reason can be rationally defended — and I have done so elsewhere.5

Essentially, the mind knows itself as fitted to know being, which is why we are so naturally certain of the basic truth that being cannot both be and not be. In like manner, the mind demands sufficient reasons for everything that exists, since, just as the mind demands reasons for everything it knows with certitude, so does it grasp this certitude in terms of the being or reality that supports it.

Thomistic philosopher Benignus Gerrity succinctly defends the principle that everything needs a sufficient reason in terms of being as follows:

“The intellect, reflecting upon its own nature, sees that it is an appetite and a power for conforming itself to being; and reflecting upon its acts and the relation to these acts to being, it sees that, when it judges with certitude that something is, it does so by reason of compulsion of being itself. The intellect cannot think anything without a reason; whatever it thinks with certitude, it thinks by compulsion of the principle of sufficient reason. When it withholds judgment, it does so because it has no sufficient reason for an assertion. But thought — true thought — is being in the intellect. The intellect is actual as thought only by virtue of some being in it conforming it to what is; whatever the intellect knows as certainly and necessarily known, it knows as the self-assertion of a being in it.”6

No One Really Thinks Something Comes From Nothing

While not every speculative thinker will grant the universal validity of the Thomistic principle of sufficient reason, it is really impossible for anyone’s mind to countenance that something could come to be from absolutely nothing at all. While some thinkers make the false claim that “existential inertia” is possible,7 it is quite another matter when something “pops into being” from nothingness, since that is the sudden appearance of something that was not at all there in the first place. It is far easier to assume that what is already in existence may continue in existence of its own accord than it is to understand how something with absolutely no prior existence should appear out of nowhere.

That is why no one really takes seriously the notion that something can come to be from absolutely nothing all by itself — since in this latter case there is not even a prior existent from which existence can continue to be.

We never, in fact, see something come from nothing. Indeed, this is why materialists hold that the universe, in some form or other, had no beginning in time. Even in the atheist’s mind, if something really came from no presupposed matter, then they fear they would have to concede God’s existence!

Even atheists implicitly recognize that being cannot come from absolute non-being. This reveals the true insight at the root of this principle (that being cannot come from non-being). This shows that the human mind absolutely grasps the nature of being and its most evident implications, since, if we did not really know the nature of being, we would never be so certain that you cannot get something from absolutely nothing — being from total non-being!

The plain fact is that no one even suggests that something could possibly come from nothing. Atheistic materialists avoid that possibility by insisting that something has always existed, specifically, something physical. So, they argue, whatever begins to exist comes to be from pre-existing matter.

Nor do theists say that something, namely this material world or any form of creation, comes to be from nothing. Theists maintain that creation may presuppose nothing finite or material, but that God has always existed and that the world proceeds from the infinite power of God’s creative act.

This shows the human mind’s absolute certitude of the truth that you cannot get something from absolutely nothing. Everyone takes it as given that whatever exists now must either have always existed, or else, come into existence in some manner from something that previously existed.

The mind sees clearly that the nature of being absolutely demands this eternal truth, namely, that being can come to be solely from being. There are no exceptions to this metaphysical rule. This shows how powerfully the mind grasps a most fundamental truth about being, one so universal and transcendental that it must necessarily govern the behavior of all beings in existence or which could ever even possibly exist!

How This Applies to the Proof from Motion

While St. Thomas’s First Way tells us that “it is certain and evident to our senses that in the world some things are in motion,”8 it is also certain and evident to our minds that things cannot cause their own motion, since motion entails the coming-to-be of something that was not previously there in the same exact way it was prior to the motion. Some new quality of existence must come-to-be — even if it is merely a difference in spatio-temporal location.

But, it is precisely because you cannot get something from nothing that things in motion require a cause of that motion — a cause that cannot already be found in the finite world in which we live. The key insight is that what is new in a change is new precisely because it possesses some distinct quality of being that distinguishes it from all that previously existed in our finite universe.

That is also the basic insight of the Aristotelian distinction between potency and act, since what is in potency to some quality is in a state of non-being with respect to that quality – while what is in act now possesses that quality. Yet, when expressed as “potency and act,” many people reject this as an archaic doctrine. And yet, considered simply as something that has non-being with respect to some specific quality, it should be just as easy to see that that “something” cannot give to itself the being it lacks as it is to see that you cannot get something from nothing.

In fact, this is the same essential insight that I have myself employed in presenting the argument from motion in a way that many might not even recognize as simply a variation on the first way of St. Thomas — since I studiously avoided using the terminology of potency and act! My argument may appear to be somewhat novel, when, in fact, it is simply St. Thomas Aquinas’s classical First Way looked at from a different perspective.9

Once again, the point of all this is not the argument itself, but to recognize that the argument rests on the basic insight that you cannot get being from non-being and that the human mind is absolutely certain of the truth of this principle because it sees its truth in the same act with which it knows the being of anything at all. We may not be able to explain why the intellect has such perfect certitude, since to understand why the mind “sees” this truth with such clarity in seeing that it identifies with being itself would require understanding why the mind exists and acts as it does. But, to know why the mind exists as it does one would have to have invented or created the mind itself, something which man has not done.

Still, it is much like skipping down stairs two at a time. We can (when young and agile enough) perform this act. But if you try to explain to yourself how you are able to do it at the same moment you are doing it, you would likely wind up in the emergency room with a broken leg! Still, this limitation on one’s knowledge in no way lessens the certitude that one is doing this athletic act when engaged in it. So, too, the inability to explain why and how the mind is so created that it can know the basic truths of being does not lessen the fact that we do so and have the ability to do so with certitude.

Maritain’s Warning

Jacques Maritain warns us not to confuse the being of metaphysics with the being of logic. In his book, A Preface to Metaphysics, the eminent metaphysician writes:

“This mistake has, in fact, been made by the moderns, many of whom maintain that this being as such is a mere word, a linguistic residuum, or else that it is a universal frame whose value is purely logical, not ontological.”10

Maritain later explains, “For by definition none of the real functions of being, but only its conceptual functions, are the proper and the direct object of logical study. There could be no more serious error than to suppose that the being of metaphysics is this being envisaged under the aspect of conceptual being. . . .”11

Again, he affirms that “. . . logic is the science of conceptual being and not a science of real being.”12

Not by mere conceptualization, which is the first act of the mind, does the intellect first grasp existence. Rather, existence is first known in a judgment. “It is to existence itself that the intellect proceeds when it formulates within itself a judgment [the second act of the mind] corresponding to what a thing is or is not outside the mind. . . . But the intellect and its act are fulfilled by existence affirmed or denied by a judgment, by existence attained — as it is lived or possessed by a subject — within the mind, within the mind’s intellectual act itself.13

Finally, the whole point of all this is that when the metaphysician talks about being, he is referring to existence or being as “esse ut exercitum,” that is, existence which is first known in a judgment “of the actual existence of corruptible things,” which is made “through the instrumentality of the senses.” On the contrary, the logician “. . . envisages esse . . . only to regard it as itself an essence, esse ut significatum [being as signified].”14

In light of all the above, it is clear why Maritain insists, “Being is not a genus, but a transcendental.”15 For, a genus is a category within the science of logic, not metaphysics.

And that is why Thomists insist that the metaphysical concept of being is analogous and able to be licitly applied both to creatures and the uncreated God, since it is not a univocal logical concept at all, but a metaphysical knowledge attained in and from an existential judgment formed when the mind encounters any reality at all.

But Are We Merely Prisoners in an Epistemic Matrix?

The bottom line is that the human mind forms the transcendental knowledge of being, not as a mere concept within the mind, but by a judgment of being based on actual encounter with reality. As Maritain puts it: Scio aliquid esse. I know something to exist.

Some have raised the skeptical hypothesis that, perhaps, our minds are inherently limited to the knowledge they have, but that this knowledge reflects only an incomplete grasp of the whole of reality. Thus, like prisoners in a matrix, we think we know universal truth, whereas we have no way of realizing that our minds do not and cannot grasp the whole of reality. Therefore, any “universal” principles our mind enunciates can never be known to be truly universal.

Now this skepticism might be warranted if all we knew of being was merely essential in nature. For example, if we encountered a chicken for the first time, we might form a concept of “chicken-ness” which would guarantee that, to paraphrase Kant, this knowledge would hold good for all possible chickens. Thus, if we encountered something and were assured that this thing was a chicken, then we would already know something of its nature. But, if we encountered a “non-chicken,” then our knowledge of chicken-ness would be of no avail. Thus, there can, indeed, be a world of things the human mind has never encountered — a world whose nature would be quite unknown to it.

But the metaphysical concept of being is genuinely transcendental, since the mind, as Benignus says above, “sees” being. Once we form the concept of being, we know that anything we can possibly encounter must be some form of being or reality. If it is, it follows the laws of being. If it is not, then there is nothing there to violate those laws. Hence, the mind does encompass all possible reality in its grasp of basic metaphysical principles.

How First Principles Can Lead to God’s Existence

I have no intention here of presenting the finished proofs for God’s existence, since my goal in this essay was simply to show that we have apodictic, objective certitude of those first principles of being that can be used to demonstrate the existence of classical theism’s God.

We have certitude of the needed first principles: identity, non-contradiction, sufficient reason, and causality. Causality flows from sufficient reason easily, the moment one realizes that a thing must either be its own sufficient reason, or, to the extent that it is not, it needs an extrinsic sufficient reason to explain that in it which it does not itself explain. That extrinsic sufficient reason is simply another name for a cause.

Starting with the evidence of our senses, St. Thomas’s famous Five Ways show that various aspects of finite things require causes, most evidently, to explain the motion found in the things that fill our physical world. That one cannot go to infinity in taking prior causes is implicit in the need for a sufficient reason for these causes, which, were they to recede to infinity, would never be fulfilled.16

As stated earlier, my purpose here is merely to show how we can be perfectly certain that some foundational principles of metaphysics are universally and transcendentally true. These principles are key premises in the proofs for God, but they are not the proofs themselves. Thus, in its primary intuition of being, the mind knows the absolute truth that things cannot both be and not be. Even atheistic skeptics constantly presume this truth to be transcendentally valid, whenever they probe for and allege that somehow the notion of God entails a contradiction in terms, for example, that evil in the world is contradictory to an all-good God. If the principle of non-contradiction were not transcendentally true, their objection would have no force.

What has justly been called the natural metaphysics of human intelligence is, therefore, critically vindicated. Every sane human being knows that things are what they are, that things cannot both be and not be from the same perspective, that things need an explanation and that if they do not explain themselves, something else must explain them. We know these things to be objectively and universally true, precisely because our minds naturally “see” being just as our senses sense sensible objects.

Despite the claims of skeptics who cannot escape presuming these same principles themselves, we are rightly certain that such knowledge of first principles of being are true, just as one cannot sit on a roofing nail and yet honestly deny the reality of a painful experience.

With these metaphysical first principles of being safely in hand, the Thomistic philosopher can then safely examine such classical proofs for God as offered by the Angelic Doctor himself in his famous Five Ways. Each way entails some starting point, such as (1) things in motion, (2) an order of efficient causes, (3) things that are able to be and not be, (4) beings that are more and less good, true, noble and the like, and (5) signs of governance of the world.17

As I said at the outset, many competent Thomists have presented complete expositions of these proofs. My sole concern here has been to defend, against the errors of modern skeptics, those basic principles of being that are foundational to such proofs. That purpose has been accomplished.

A Postscript on Epistemological Realism

Epistemological realism claims that our primary knowledge is of a real world existing independently of human knowledge. While epistemological realism is not itself a metaphysical first principle, St. Thomas begins all his proofs for God’s existence with the data of direct sense experience of the physical world around us. This is not a matter of merely accepting common sense, but is based on critical reflection as well.

Without presenting a full study of epistemology, one can still make the case for epistemological realism by reflecting on the logical presuppositions of natural science. Since most skeptics today accept the findings of natural science, one need merely notice that the entire scientific method presupposes our being able to take measurements and observations of the physical world around us. This is to presuppose epistemological realism.

Nonetheless, I would note that some proofs, such as the one from motion, need not depend on epistemological realism anyway. That is because, even if all we knew was merely internal, subjective experiences, we could still argue to God’s existence from the reality of subjective changes that are immediately evident within subjective experience.

  1. Dennis Bonnette, Aquinas’ Proofs for God’s Existence (Martinus-Nijhoff: The Hague, 1972).
  2. For example, among classical commentators would be included John Capreolus, John of St. Thomas, Sylvester of Ferrara, Dominico Banes, and Cajetan. More eminent contemporaries would include A.D. Sertillanges, Reginald Garrigou-Lagrange, Etienne Gilson, Jacques Maritain, Cornelio Fabro, Victor Preller, Joseph Owens and others.
  3. Dennis Bonnette, “The Principle of Non-Contradiction’s Incredible Implications,” Strange Notions,
  4. Jacques Maritain, The Degrees of Knowledge (New York: Charles Scribner’s Sons, 1959), 71–81.
  5. Dennis Bonnette, “‘Existential Inertia’ vs. Almighty God,” Strange Notions,
  6. Benignus Gerrity, Nature, Knowledge, and God (Milwaukee, WI: Bruce Publishing Company, 1947), 400–401.
  7. Bonnette, “‘Existential Inertia’ vs. Almighty God.”
  8. Summa Theologiae, I, a. 2, q. 3, c.
  9. Dennis Bonnette, “How ‘New Existence’ Implies God,” Strange Notions,
  10. Jacques Maritain, A Preface to Metaphysics (New York; Sheed & Ward, 1939), 27.
  11. Maritain, A Preface to Metaphysics, 36.
  12. Maritain, A Preface to Metaphysics, 42.
  13. Maritain, A Preface to Metaphysics, 21.
  14. Maritain, A Preface to Metaphysics, 38.
  15. Maritain, A Preface to Metaphysics, 37.
  16. Dennis Bonnette, “Why An Infinite Regress Among Proper Causes Is Metaphysically Impossible,” Strange Notions,
  17. Summa Theologiae, I, a. 2, q. 3, c.
Dennis Bonnette, PhD About Dennis Bonnette, PhD

Dennis Bonnette, PhD, retired in 2003 as a full professor of philosophy at Niagara University in Lewiston, New York, where he was chairman of the philosophy department from 1992 to 2002. He received his doctorate in philosophy from the University of Notre Dame in 1970. Dr. Bonnette taught philosophy at the college level for more than 40 years, and continues teaching, offering free courses at the Aquinas School of Philosophy. He has published many scholarly articles and two books, with the third edition of his Origin of the Human Species (Sapientia Press) appearing in 2014. His web site is


  1. Christos Yannaras convinced me how wrong-headed and destructive this mindset is to Christianity and how the Western Church went drastically off course the moment Anselm put pen to paper.


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