Kirk MacGregor’s New Natural Theological Argument for the Trinity

I've been attending the Evangelical Philosophical Society (EPS) meetings since 2015. They are always a highlight of my year as I get to travel to new cities and meet thousands of like-minded people from around the world. Many of these people are my heroes. Many others are my “frienemies”—brothers and sisters in Christ who love me but oppose some of my theological positions (and that sentiment is mutual). One thing is for sure: it’s always iron sharpening iron (Prov. 27:17).

I often present papers that I’ve been working on at these events, and I absolutely love listening to my heroes and frienemies present papers themselves.

But last November, in Boston at the 2025 EPS meeting, I had the privilege of listening to one of my heroes give what might be the best paper I’ve ever heard at an EPS conference—yes, even better than the one I gave with my coauthor Phil Kallberg at the same event (click here to watch Is Divine Determinism a Different Gospel?).

Dr. Kirk R. MacGregor—who wrote the foreword to the first edition of my book Human Freedom, Divine Knowledge, and Mere Molinism—has taught me so much over the years. He has taken me under his wing and helped me transition from a “mere online apologist” into a philosophically inclined theologian who contributes to the academic literature. In my opinion, when it comes to Molinism, he’s top of the line.

This year, however, MacGregor expanded his mastery of philosophical theology and applied his high-powered brain to something many have long requested: a natural-theological argument for the Trinity.

Can the Trinity Be Known Apart from Scripture?

For years, people have been asking whether it is possible to argue for the Trinity without appealing to Scripture—using only reason and natural theology.

We’ve gotten close.

Some philosophers have argued that the one true God must be at least a duality—that perfect love requires more than a solitary individual. Although such arguments do not prove the Trinity, the Trinity certainly makes sense of them. My good friend and colleague Dr. Adam Lloyd Johnson wrote his doctoral dissertation on this topic and recently published it as a book titled Divine Love Theory. The idea, roughly, is that objective moral goodness—and especially love—finds its ultimate grounding in the eternal, triune love relationship within God Himself.

Arguments like these are excellent. They show that Christianity makes sense of objective morality and that love is more fundamental to ultimate reality than the physical universe. That’s pretty cool.

Others, like William Lane Craig, have done tremendous work showing that the concept of the Trinity is logically coherent. Contrary to what is often said from pulpits, the Trinity is not a contradiction or an incomprehensible paradox. When I hear someone say that, I usually respond with: “Speak for yourself. I understand it just fine—and so do hundreds of teenagers I’ve trained on MAVEN trips over the years!”

To put it simply: "God is one what and three whos."

Where’s the contradiction?

Notice what I did not say. I did not say God is one person and three persons. I did not say God is one God and three Gods. Those are contradictions--and therefore, false. This is proper: God is one what (one being or substance) and three whos (three persons).

A Helpful Illustration: Cerberus

To help connect these dots, consider an illustration William Lane Craig has made famous.

I do not think the Trinity is as “mysterious” as most people assume. Much of this clarity comes from my study of the immaterial soul and substance dualism. I do not merely have a soul; rather, I am a soul who has a body—and who can survive the death of that body. One day, I will receive a glorified body.

If that is coherent, then it is coherent to say that God is one immaterial substance with three sets of cognitive faculties.

While most analogies of the Trinity fail (and often cross the line into heresy), Craig offers an illustration that—while admittedly controversial—helps illuminate key concepts.

Cerberus is the three-headed guard dog of Greek mythology. The three heads cooperate to function as one effective guard dog. The idea of a three-headed animal is not incoherent. In fact, when my son was in elementary school, he once found a two-headed snake in the neighbor's yard. If two-headed snakes can exist, then a three-headed dog is at least conceivable.

Now imagine Hercules is bitten by Cerberus. Would he say, “Cerberus bit me,” or “One of Cerberus’ heads bit me”? Either statement would make sense. Cerberus is one canine being, yet each head is also canine because it is a part of Cerberus.

Now suppose Cerberus is a rational creature with three minds—or three sets of cognitive faculties. Each head could say, “I think that…”. If Cerberus is slain and survives bodily death as an immaterial soul, then it is conceivable that one immaterial soul substance exists with three centers of consciousness.

Of course, this illustration is imperfect. Cerberus—whether considered as a three-headed dog or as a single immaterial soul with three centers of consciousness—is still a finite, created, contingent being, whereas God is necessary, maximally great, and divine. The point of the illustration is modest: it shows the conceptual coherence of one substance with three whos—not a metaphysical identity between God and a mythical dog.

If this is conceivable for Cerberus, it is certainly not a problem for a maximally great God.

But What If We Didn’t Have the Bible?

Now for the big question.

Suppose a deep-thinking person were born on a remote desert island with no access to Scripture. Could that person, through reason alone, come to the conclusion that a maximally great God exists—and that this God is tri-personal?

If Kirk MacGregor were stranded on that island, the answer is a resounding yes!

Here is Kirk MacGregor’s New Natural Theological Argument for the Trinity—presented exactly as he formulated it:

Kirk MacGregor’s Argument

1. God is the one and only maximally great being.

2. A maximally great being essentially possesses every great-making property.

3. Being all-loving is a great-making property.

4. Therefore, God is essentially all-loving (from 1 – 3).

5. Love possesses two essential qualities: selfless mutuality and non-possessiveness.

6. Therefore, God is essentially selflessly mutual and essentially non-possessive (from 4 – 5).

7. Selfless mutuality requires a community of at least two persons.

8. Non-possessiveness requires a community of at least three persons.

9. Therefore, God is essentially a community of at least three persons (from 6 – 8).

10. Any divine person must exist necessarily, not merely contingently.

11. Exactly three divine persons are necessary and sufficient to fulfill the conjunction of selfless mutuality and non-possessiveness.

12. Therefore, any community of divine persons greater than three will include at least one member who exists contingently (from 11).

13. Therefore, no community of divine persons can be greater than three (from 12, 10).

14. Therefore, God is essentially a community of exactly three persons (from 9, 13).

BOOM!

MacGregor did it.

This argument does not appeal to a single verse of Scripture. It relies solely on perfect-being theology, careful reasoning, and reflection on the nature of love. Of course, every premise can be discussed and debated—but the argument shows that a natural-theological case for the Trinity is not only possible, but serious and sophisticated.

Dr. MacGregor has not yet published this argument, but he graciously gave me permission to share it here. He will be joining us on the FreeThinking Ministries YouTube channel soon to defend the premises and answer objections.

If you have questions, pushback, or objections, drop them in the comments below—and let us know what we should ask him.

Stay reasonable (Isaiah 1:18),

Dr. Tim Stratton