Why Does Anything Exist? The Esse-Essence Argument for God

You know exactly what a unicorn is: a horse with a horn, more or less. You can picture it, describe it, define it. So why aren't there any? What's missing?

The thing that's missing is what Thomas Aquinas calls esse: the act of existing. And the fact that it's missing from unicorns but present in horses tells you something important. What a thing is and whether a thing is are two genuinely different features of reality. This is Aquinas's distinction between essence and esse, and if you follow it carefully, it leads to one of the most powerful arguments for the existence of God ever constructed.

In the video, I walked through the core of the argument. In this post, I want to fill in the material I had to skip: the different types of infinity, the objections to the causal principle, and the debate over whether "subsistent esse" is even a coherent concept.

Part 1: The Esse/Essence Distinction

The argument begins with an observation. Take any real thing: a horse, a tree, a human being. There are two aspects to it. Its essence (what it is) and its esse (the fact that it is). Your essence is everything that makes you the kind of thing you are: rational animal, biological organism, embodied consciousness. Your esse is the sheer actuality of you being here rather than not being here.

These two are genuinely distinct. You can fully understand what a phoenix is without knowing whether one exists. You can understand the entire essence of "human being" without that telling you whether any particular human being is actual. If essence and esse were identical, understanding what a thing is would automatically settle whether it exists. But it doesn't. So they're distinct.

An important clarification: "distinct" doesn't mean "separable." You can't peel the esse off a thing and put it on a shelf. They're distinct the way a heart and its beating are distinct. You never encounter one without the other in a living body, but they're genuinely different principles. The heart is the structure; the beating is the activity that makes it alive. Essence is the structure of a thing; esse is the act that makes it real.

From this, Aquinas draws a critical conclusion: since esse isn't part of any essence, it must come to the essence from without. It's not something the essence generates on its own. It's received. And anything that receives its esse from something else is, in the relevant sense, caused.

Part 2: Could There Be Something Whose Essence Is Esse?

If every ordinary thing has esse distinct from its essence, is there anything where that distinction collapses, where what-it-is just is the act of existing?

Aquinas argues that if such a being existed, it would be what he calls subsistent esse, or self-standing existence. Not a thing that happens to exist, but existence itself, standing on its own. And he argues there could only be one such being, because there are only three ways to multiply a thing, and none of them work for pure esse.

You can multiply something by adding a differentiating feature, the way "animal" is multiplied into species by adding "rational" or "equine." But if you add anything to pure esse, it's no longer pure. You can multiply something by receiving a form in diverse matter, the way the form "horse" is multiplied into many individual horses. But subsistent esse can't be material, because material beings depend on matter for their being, and subsistent esse depends on nothing. Or you can have an absolute thing received in multiple subjects, the way the sun's heat is received in many objects. But that's not multiplying the source; it's participation. The sun is still one.

So if subsistent esse exists, there's exactly one of it.

Part 3: The Causal Argument

Now the argument proper. Every esse/essence composite receives its esse from outside itself. A thing can't cause its own existence; it would have to exist before it existed. So every composite depends on an extrinsic cause for its esse.

This generates a causal chain. Each composite gets its esse from something. If that something is also a composite, it too depends on a further cause. The question is whether this chain can extend infinitely.

Part 4: The Types of Infinity

This is the part I skipped in the video, and it's important, because Aquinas doesn't just assert that an infinite regress is impossible. His position is more nuanced than that.

Actual vs. Potential Infinity

A potential infinity is a series that can always be extended by one more member, but which is never actually completed. Think of counting: you can always add one more number, but you never arrive at a completed infinity. Time, for Aquinas, is potentially infinite in this sense. One moment follows another without end, but the whole series is never "all there" at once. The same goes for the division of a continuum: you can always divide further, but you never finish dividing.

An actual infinity is a completed totality with no terminus, like a line that extends infinitely in both directions, fully present all at once.

Per Se vs. Per Accidens Causal Series

This distinction matters even more than the actual/potential one.

A per accidens causal series is one where each cause does its work and then steps aside. Think of a father and son. The father causes the son to exist, but then the father can die and the son goes on existing and can father his own children. Each link in the chain is independent of the others. The replacement saws a builder goes through are another example: one saw breaks, you get another. There's no causal dependency between the first saw and the second. The relation between them is succession, not dependency.

Aquinas actually allows that a per accidens series might extend to infinity. It's conceivable that fathers have been begetting sons forever, with no first father. Nothing in the logic of the series demands a first member, because each link is self-standing once it exists.

A per se ordered causal series is fundamentally different. In this kind of series, every member depends on the prior member right now, in this very moment, for its causal power. The classic example: a hand pushes a stick, which pushes a stone. The stone only moves because the stick is pushing it, and the stick only pushes because the hand is moving it. Take away the hand and the whole chain goes dead.

In a per se series, an infinite regress is impossible. Here's why. No intermediate member in the series has any causal power of its own. Each one is an instrument; it only causes insofar as it's being actuated by something prior. If the series extends infinitely, then you have an infinite line of instruments with no agent. Every mirror is reflecting, but there's no light. Every link in the chain is borrowing power, but nobody has any power to lend.

Why the Esse Chain Is Per Se

Aquinas's critical move is to argue that the causal chain of esse is per se, not per accidens. And the reason is straightforward. In a per accidens series, the cause can cease to be without its effect ceasing to be. The father dies; the son keeps existing. But an esse/essence composite cannot exist apart from whatever is causing its esse right now. It doesn't have esse essentially; it only participates in it. So the cause of its esse must be operating at every moment, not just at some point in the past.

This means the chain of esse must terminate in a first cause: something that has causal power with respect to esse in its own right, not derivatively.

Part 5: Objections to the Causal Principle

The causal premise of the argument (that every esse/essence composite requires a cause for its esse) has attracted significant pushback. Here are the main objections and the Thomistic responses.

Objection 1: Esse as a Brute Primitive

Why can't esse just be a brute fact, an uncaused, non-intrinsic property that simply obtains with no explanation?

The Thomistic response: this doesn't work once you understand what essence and esse are. Essence and esse are related as potency and act. No essence would exist without esse; the essence is a capacity for existence, and esse is the actualization of that capacity. And no esse/essence composite needs to exist; its non-existence is always conceivable. Given both of these facts, the question "Why does this essence have esse rather than not?" is a perfectly reasonable one, and it demands a cause.

Objection 2: Hume on Constant Conjunction

Hume argued that causation is just regular succession, one event following another. We never observe a necessary connection between cause and effect; we only observe patterns. If that's right, Aquinas's causal principle (that esse requires a cause) is just a generalization from experience that could, in principle, fail.

The response comes in two parts. First, Hume's argument proves too much. As Elizabeth Anscombe pointed out, you can conceptually separate a rose from its particular shade of red, but you can't separate a rose from color in general. Analogously, you can separate a particular cause from a particular effect, but that doesn't mean cause and effect are separable as such. Second, we do in fact experience necessary connections: dependent properties like risibility (the capacity to laugh), which clearly depends on rational nature, or light in the air, which clearly depends on the sun. These aren't mere regularities; they're intelligible dependencies.

Objection 3: Causation Is Unobservable

A stronger Humean line: there is nothing in experience that reveals a necessary connection between cause and effect, so necessary connection is not an objective feature of the world.

The Thomistic response: this claim only follows if you accept Humean empiricism, the view that all we receive from experience are atomic sense impressions with no inherent intelligibility. But Humean empiricism has its own problems. On that view, we only ever receive the empirical counterparts of objects: raw sense data that carry no conceptual content. If that's right, then our sense data can't inform any judgment about reality, and they can't function as justification for any judgment either. The framework that was supposed to make causation less obscure ends up making everything less intelligible.

Objection 4: Causality Needs Reductive Analysis

Some philosophers argue that causal notions like necessity and dependency are obscure and need to be re-parsed in cleaner terms, ideally in purely extensional terms amenable to first-order quantificational logic.

The Thomistic response: the demand for reductive analysis presupposes that the extensional, quantificational framework is the clear one. But that framework is only "clearer" if you've already accepted the empiricist assumptions that motivate it. The Aristotelian-Thomistic framework has its own account of clarity: intelligible connections between act and potency, cause and effect, form and matter. Insisting that these be re-parsed in Humean terms is begging the question.

Objection 5: Stroud's Indispensability Argument

Barry Stroud argued that the necessary connection between cause and effect is indispensable to our thought about the real world, but that this shows it's a feature of our thought rather than of the world itself.

The Thomistic response is blunt: this is a non sequitur. The fact that a concept is indispensable to thought about reality doesn't entail that it's merely a feature of thought. The indispensability might be evidence that the concept tracks something real.

Part 6: Is Subsistent Esse Even Coherent?

Even if the argument's logical structure is sound, several philosophers have challenged the conclusion itself: the idea that there could be a being that just is existence. These objections are worth taking seriously.

Kenny's Objection: Existence Isn't a Real Predicate

Anthony Kenny argued that subsistent esse is absurd. Existence, he claimed, can only mean one of two things: specific existence (what it is for a given species to be instantiated, roughly in Frege's quantificational sense) or individual existence (the existence of this particular horse, this particular human). God can't be specific existence, because there's no species for God to instantiate. And God can't be individual existence, because individual existence is just the fact of being what you are, which doesn't entail anything ontologically special.

The Thomistic response: Kenny is importing a Fregean framework and insisting Aquinas play by its rules. But Aquinas doesn't share that framework. For Aquinas, esse is not a quantifier or a logical predicate. It's the most fundamental act in reality, the act by which anything is real at all. Kenny's objection assumes the very view of existence that Aquinas is rejecting. And the Fregean view has its own unresolved problems, particularly when it comes to accounting for the existence of individuals as opposed to the instantiation of concepts.

Kenny's Second Objection: No Esse/Essence Distinction

Kenny also argued that there is no real distinction between essence and esse, that the existence of an entity is simply tied to its essence.

The response: this assumes Aquinas treats essence and esse as separable parts, like bricks in a wall. But they're not parts; they're principles, the way matter and form are distinct principles in Aristotle's hylomorphism. You can't separate form from matter in a material substance, but they're still really distinct. The same goes for essence and esse.

Kenny's Third Objection: God as a Minimal Property

If God is pure esse, Kenny argued, then God is at best the thinnest, most minimal property that everything shares: bare existence, the lowest common denominator of reality.

The response: this confuses two things Aquinas carefully distinguishes. Esse commune is the common existence shared by all things, the bare fact that things exist, considered abstractly. It is indeed thin and minimal. But esse divinum is existence that admits of no further addition because it is already complete and perfect in itself. It's not the lowest common denominator; it's the fullness of actuality from which everything else derives by participation. Esse commune participates in esse divinum. Confusing the two is like confusing the light reflected in objects with the sun itself.

Plantinga's Objection: Properties Need Subjects

Alvin Plantinga objected that esse is a property, and properties can't exist on their own. They need subjects to be instantiated in. So "subsistent esse" is incoherent.

The Thomistic response: this gets the ontological order backwards. Ordinary properties depend on their subjects. Redness depends on the rose; shape depends on the object. But esse is not an ordinary property. Esse is that without which there would be no subject at all. It's not that esse needs a subject to exist in; it's that subjects need esse to exist. Insisting that esse must inhere in a subject is like insisting that a cause requires its effect. It reverses the direction of dependence.

Plantinga's Second Objection: This Isn't the God of the Bible

Plantinga also pressed the question of whether subsistent esse could possibly be a personal God, the kind of being who speaks, acts, loves, and enters into covenants.

Eleonore Stump offered one response: God can be both esse (when considered as the source from which all being flows) and ens, an entity or individual being (when considered in Himself). This is counterintuitive, but reality sometimes is. Photons are both particles and waves. The deeper reality admits of descriptions that seem opposed at a lower level of analysis. Other Thomists take a more direct route: esse tantum (a being that is nothing but the act of existing) is a subsisting individual, and there is no principled reason a subsisting individual can't be personal.

Part 7: The Argument Summarized

(1) In everything we experience, essence (what a thing is) and esse (that a thing is) are really distinct.

(2) Whatever has esse distinct from its essence does not account for its own existence.

(3) What does not account for its own existence receives its esse from an extrinsic cause.

(4) The causal chain of esse is a per se ordered series, where each member depends on the prior right now.

(5) A per se ordered series cannot regress to infinity.

(6) Therefore, there must be a first cause of esse.

(7) The first cause cannot be an esse/essence composite (otherwise it would need a cause for its own esse).

(8) So the first cause must be a being whose essence is its esse: subsistent esse.

(9) There can be at most one subsistent esse.

(10) Therefore, there exists exactly one being that is pure subsistent existence, and this is what we call God.

Conclusion

What makes this argument distinctive is where it starts. It doesn't begin with the motion of the planets or the fine-tuning of physical constants. It begins with the most basic fact about anything real: that it didn't have to be real. The gap between what a thing is and the fact that it is, a gap so ordinary we barely notice it, turns out to demand an explanation. And when you follow the explanation to its terminus, you arrive at something that has no gap: a being whose very nature is to be.

The objections are serious, and I've tried to present them fairly. But I think the Thomistic responses hold up. The Fregean and Humean frameworks that generate the strongest objections have their own deep problems, and in many cases the objections rest on importing assumptions that Aquinas has principled reasons to reject.

Whether you find the argument convincing or not, it deserves to be understood on its own terms. And those terms (essence, esse, act, potency, participation) are richer and more precise than they first appear. Aquinas wasn't playing word games. He was trying to answer the most fundamental question there is: why is there something rather than nothing?