The Modal Trilemma Argument for the Necessary Existence of God
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Definition
By God I mean an omnipotent, omniscient, morally perfect personal being.
Necessary existence is not included in this definition. The argument does not begin by defining God as necessary. Instead, it begins with the familiar attributes traditionally associated with maximal greatness and examines what follows from them.
The goal of the argument is to determine the modal status of such a being—whether such a being would be impossible, contingent, or necessary.
⸻
Clarifying A Priori Reasoning
Before presenting the argument itself, it is important to clarify how a priori reasoning from properties works. Critics sometimes claim that statements such as “God is good” are trivial because goodness is supposedly built into the definition of God. But this confuses a tautology with a genuine a priori inference.
Consider a simple geometric example.
Geometric version
1.If a shape has eight equal sides and eight equal angles, then it is an octagon.
2.This shape has eight equal sides and eight equal angles.
Therefore:
This shape is an octagon.
The conclusion follows necessarily, but it is not a meaningless restatement. Instead, we identified a set of properties that entail octagonhood.
Now consider a parallel structure in the moral case.
Moral version
1.A being with perfect knowledge of all value-relevant facts and perfect power to act on that knowledge cannot fail to do what is objectively best.
2.A maximally great being possesses perfect knowledge and perfect power.
Therefore:
The maximally great being is morally perfect.
If a being is morally perfect in every possible situation, it is good. Thus the statement “God is good” is not definitional but the conclusion of a chain of reasoning.
Just as
eight equal sides + eight equal angles → octagon
we get
perfect knowledge + perfect power → moral perfection → goodness.
Understanding this structure matters because the modal reasoning below proceeds in the same way: it does not define God into existence but explores what follows from the attributes of maximal greatness.
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The Argument
Premise 1
God is defined as an omnipotent, omniscient, morally perfect personal being.
These attributes describe a being that would possess maximal power, maximal knowledge, and perfect goodness.
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Premise 2
Every candidate being must fall into one of three modal categories: impossible, contingent, or necessary.
A being is impossible if it cannot exist in any possible reality.
A being is contingent if it exists in some possible realities but not others.
A being is necessary if it exists in every possible reality.
These three possibilities exhaust the modal options.
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Premise 3
If God exists, God would be the ultimate foundation of reality.
A being with unlimited knowledge, power, and moral perfection would not merely be another object within reality but the deepest explanatory ground of it.
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Premise 4
The ultimate foundation of reality cannot be contingent.
If the ultimate ground of reality existed in some possible realities but not others, we would need an explanation for why it exists here but not there.
Either something external explains the difference, the being’s own nature explains it, or the distribution is brute.
External explanation undermines ultimacy.
Internal explanation yields necessity.
Brute distribution would make the ultimate foundation of reality arbitrary.
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Premise 5
Therefore a maximally great being must be metaphysically independent.
A maximally great being cannot depend on external causes or unexplained modal distribution. Its existence cannot flicker on and off across possible realities.
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Premise 6
If God exists at all, God must exist necessarily rather than contingently.
Once contingency is ruled out for a maximally great being, the remaining modal options are necessity or impossibility.
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… continued in comment below
@LatFilosof@TheDrewHaas@limitandmind I still stand by my response. His tableau is correct; but the it doesn’t change the fact that if God’s not contingent, the only way it’s possible God does not exist is for him to be totally and entirely impossible across all possible worlds. Is he?
@LatFilosof@TheDrewHaas@limitandmind If God is not contingent then God’s nonexistence is only possible if God is entirely impossible. So the question is, is he? Why? How?
Which is why I’ve tried to strictly break the MOA down to this: which modal category does the MGB (God) belong in? Necessary (existing in all possible worlds), contingent (existing in some but not all possible worlds), or impossible (existing in exactly 0 possible worlds)
I feel like that’s the least question begging way to do it. The funny thing is, I’ve put AI to the ringer on this and it has consistently over and over and over affirmed that God is actually metaphysically necessary when you force it to choose between necessary, contingent, or impossible (and sometimes having to point out to it when it says such a being can’t be contingent but later starts trying to act like it might be contingent)
@LatFilosof@TheDrewHaas@limitandmind From where I’m sitting, there is no difference between God being contingent and God being equally possible or not possible across all possible worlds.
Can you expand on how there is?
@LatFilosof@TheDrewHaas@limitandmind And this is doing the inevitable dance of treating God as contingent even after we logically rule out contingency for a Maximally Great Being.
It’s exhausting but I get why everyone’s minds keep going back to them being “equal” and God is still “possible” as ≠ contingent MGB.
It keeps things symmetrical by fiat when they’re really not. The argument below (actually posted as a comment on Joe’s post) makes it so that you can’t just say “okay so there’s a possible world God exists in, and if he’s possibly necessary then he exists in all of them, but here’s this one world he doesn’t exist in, so then he doesn’t exist in any of them.”
That’s keeping contingency alive when it’s already been ruled out for the Maximally Great Being. You’d need to be able to explain why God is impossible in all worlds, not just one, if you accept God can’t be possibly contingent and this is why:
Major Premise 1:
The Maximally Great Being (MGB) is defined as a being that exists necessarily if he exists at all.
Formally: □(G → □G).
Minor Premise 2:
A contingent being is one that exists in some but not all possible worlds.
Formally: ◇G ∧ ¬□G.
Premise 3:
In S5 modal logic, if something is possibly necessary, it is necessary.
Formally: ◇□p → □p.
This is what makes the modal ontological argument (MOA) non-probabilistic and binary.
Premise 4:
The Reverse Modal Ontological Argument (RMOA) mirrors the MOA only in form by beginning with ◇¬G (“it is possible that the MGB does not exist”).
However, once the MGB is defined by □(G → □G), this “symmetry” collapses: asserting ◇¬G means claiming that a necessarily existent being is possibly nonexistent—an incoherent move in S5.
In S5, ◇¬G → □¬G can only hold if the concept of an MGB is impossible (internally contradictory), not if it is merely “possibly false.”
Premise 5:
From (1) and (3), we derive that ◇G ⇒ □G; therefore, assuming ◇¬G directly conflicts with (1), because the MGB’s necessary existence precludes possible non-existence unless the very concept of maximal greatness is incoherent.
Intermediate Conclusion 6:
Thus, both {□(G → □G), ◇G ∧ ¬□G} and {□(G → □G), ◇¬G} are inconsistent in S5.
A “contingent MGB” cannot exist.
The only two coherent modal outcomes are:
• □G (God necessarily exists), or
• □¬G (God is impossible).
Premise 7:
Weaker modal systems (K, T, S4) restrict accessibility between possible worlds, preventing an evaluation of God from the entire modal landscape.
Doing so implicitly localizes God to certain worlds and makes him contingent by definition (which, as established in the premises above, is impossible).
Premise 8:
Participation in the full ensemble of possible worlds is what grounds the MGB’s necessity.
If you limit your modal field to partial accessibility, you lose transworld necessity and end up analyzing a regional deity—a “god” who was never the MGB in the first place.
Final Conclusion 9:
Therefore, moving the argument out of S5 into a weaker system is not an improvement but a retreat that confuses necessity with contingency and destroys the coherence of the MGB concept.
The only serious metaphysical options in S5 are:
- □G (God necessarily exists), or
- □¬G (God is impossible).
Coda 10 – Pascal’s Wager:
Pascal’s Wager does not engage any of this real metaphysics.
It treats “possibility” as a matter of personal risk assessment, not modal necessity.
It’s a probabilistic parlor game beside the genuine philosophical contest of S5, where the question isn’t whether belief pays off but whether the MGB is possible or impossible in principle.
My day job is insurance. I feel like most insurance professionals have no idea how useful a good understanding of modal logic could be for them.
@limitandmind and I have had a couple really cool convos about this in the past because he’s on the data/probability (actuarial) side of things and I’ve been on risk selection and management.
Knowing what sort of things are possible or necessary under x/y/z conditions is what it’s all about. I’m not trying to grand stand here, but at the end of the day, it’s not all that complicated. You can even get into it with evolution (which I know you love to think and write about).
After all, evolution isn't just a story about what happened. It's a story about what could’ve happened and what couldn't and what still could or couldn’t happen. Certain mutations are possible. Others aren't. Certain biological structures can arise under particular constraints. Others seem to be ruled out by chemistry, physics, or genetics. I’d go as far as to say a lot of biological structures get ruled out just by the laws of logic alone. All of that is modal reasoning.
@LatFilosof@TheDrewHaas@limitandmind I believe it’s pretty straightforward that S4 (or K or T) doesn’t allow you to access the entirety of modal space, so there’s absolutely no way to be able to tell if a being is possibly necessary in anything other than S5.
I would be happy to talk to Joe or anyone else about it.
I’ve been studying modal logic very hard for a few years now and it gets so badly abused, I don’t blame anyone for disliking it. The various logics have their uses, but what Schmid did with the MOA/RMOA and moving the argument to a weaker logic is a perfect example of why it rightfully gets hated on.
S5 is the only logic you can use to determine if something is possibly necessary. S4 and any other weaker logic doesn’t allow you to access all possible worlds, so you’d have no way of ever distinguishing between a contingent or necessary thing.
I don’t think this is done intentionally to stack the deck or anything like that, but they would argue the deck is stacked in God’s favor. It is not. Anything can only be either necessary, contingent, or impossible. The system itself is indiscriminate. It solely depends on a particular thing’s intrinsic properties (i.e. essence, haecceity) to determine which of the 3 categories the thing belongs in.
It’s a shame it is so misunderstood. Because I’ve become utterly convinced it’s the best way to examine God’s existence. You can take a simple argument such as the one below and it’s logically and metaphysically fool proof. But epistemologically our minds play tricks on us and we end up making ridiculous points like Brandon T Adams in the comments does, which never actually refutes that God is possible and therefore necessary.
If you can convince me just one of these premises is false, I will drop out of my doctoral program now and never step foot in church again:
1. Any candidate being is either necessary, contingent, or impossible.
2. An omnipotent and omniscient being cannot be contingent, because contingency would require some deeper modal reality determining its existence, undermining its maximal knowledge and power, and making it less fundamental than the reality upon which it depends.
3. No contradiction, incoherence, or modal defect has been shown in the concept of such a being; therefore, God is not impossible.
C. Therefore, God is necessarily existent, and it is impossible for God not to exist.
This actually tells us a lot. Mainly that Matthew probably did actually write his gospel first. Mark was in a hurry to translate it from Aramaic to Greek while the church in Rome was running for their lives to not be turned into Nero’s “human street lamps.”
Christians already knew the very same creed Paul recites in 1 Corinthians 15:3-7 as the first/most important thing he learned about following Christ (which was also the first/most important thing he taught others about following Christ) and we know these missionary journeys were already happening in the early 40s AD, and the creed itself is obviously prior to that.
What does the creed say? Just that Christ died, was buried, resurrected, and then appeared to a crap ton of people, including people who previously didn’t accept his Messianic claims.
So yeah, the belief that Jesus was resurrected goes back to immediately after Jesus death. Everyone knew about it. Mark didn’t have to include it in a sloppy, hurried account about what all went down during Jesus ministry for the Greeks who couldn’t read Matthew’s Aramaic gospel to know about and encourage them while they were running for their lives.
This actually tells us a lot. Mainly that Matthew probably did actually write his gospel first. Mark was in a hurry to translate it from Aramaic to Greek while the church in Rome was running for their lives to not be turned into Nero’s “human street lamps.”
Christians already knew the very same creed Paul recites in 1 Corinthians 15:3-7 as the first/most important thing he learned about following Christ (which was also the first/most important thing he taught others about following Christ) and we know these missionary journeys were already happening in the early 40s AD, and the creed itself is obviously prior to that.
What does the creed say? Just that Christ died, was buried, resurrected, and then appeared to a crap ton of people, including people who previously didn’t accept his Messianic claims.
So yeah, the belief that Jesus was resurrected goes back to immediately after Jesus death. Everyone knew about it. Mark didn’t have to include it in a sloppy, hurried account about what all went down during Jesus ministry for the Greeks who couldn’t read Matthew’s Aramaic gospel to know about and encourage them while they were running for their lives.
In The Dark Knight, Alfred tells the story about the thief in Burma who stole precious gems only to throw them away. His point was that some people just want to see the world burn.
The Joker burns a mountain of cash just to prove that money, power, and the systems built around them don’t matter to him.
Now obviously the Joker is evil. Murder is evil. Chaos for its own sake is evil. But I’ve always thought Alfred’s insight was only half baked. There are actually two very different reasons someone might want to see the world burn:
1) because they hate the world.
2) because they think the world deserves better.
Maybe that’s why Revelation doesn’t end with civilization being gradually improved. It ends with heaven and earth being destroyed and a new creation taking its place.
So if wanting corruption, greed, death, lies, pride, injustice, and every rotten thing built on top of them to burn makes me sound a little like the Joker, then so be it. I’m not rooting for the fire. I’m rooting for what comes after it.
The Modal Trilemma Argument for the Necessary Existence of God
⸻
Definition
By God I mean an omnipotent, omniscient, morally perfect personal being.
Necessary existence is not included in this definition. The argument does not begin by defining God as necessary. Instead, it begins with the familiar attributes traditionally associated with maximal greatness and examines what follows from them.
The goal of the argument is to determine the modal status of such a being—whether such a being would be impossible, contingent, or necessary.
⸻
Clarifying A Priori Reasoning
Before presenting the argument itself, it is important to clarify how a priori reasoning from properties works. Critics sometimes claim that statements such as “God is good” are trivial because goodness is supposedly built into the definition of God. But this confuses a tautology with a genuine a priori inference.
Consider a simple geometric example.
Geometric version
1.If a shape has eight equal sides and eight equal angles, then it is an octagon.
2.This shape has eight equal sides and eight equal angles.
Therefore:
This shape is an octagon.
The conclusion follows necessarily, but it is not a meaningless restatement. Instead, we identified a set of properties that entail octagonhood.
Now consider a parallel structure in the moral case.
Moral version
1.A being with perfect knowledge of all value-relevant facts and perfect power to act on that knowledge cannot fail to do what is objectively best.
2.A maximally great being possesses perfect knowledge and perfect power.
Therefore:
The maximally great being is morally perfect.
If a being is morally perfect in every possible situation, it is good. Thus the statement “God is good” is not definitional but the conclusion of a chain of reasoning.
Just as
eight equal sides + eight equal angles → octagon
we get
perfect knowledge + perfect power → moral perfection → goodness.
Understanding this structure matters because the modal reasoning below proceeds in the same way: it does not define God into existence but explores what follows from the attributes of maximal greatness.
⸻
The Argument
Premise 1
God is defined as an omnipotent, omniscient, morally perfect personal being.
These attributes describe a being that would possess maximal power, maximal knowledge, and perfect goodness.
⸻
Premise 2
Every candidate being must fall into one of three modal categories: impossible, contingent, or necessary.
A being is impossible if it cannot exist in any possible reality.
A being is contingent if it exists in some possible realities but not others.
A being is necessary if it exists in every possible reality.
These three possibilities exhaust the modal options.
⸻
Premise 3
If God exists, God would be the ultimate foundation of reality.
A being with unlimited knowledge, power, and moral perfection would not merely be another object within reality but the deepest explanatory ground of it.
⸻
Premise 4
The ultimate foundation of reality cannot be contingent.
If the ultimate ground of reality existed in some possible realities but not others, we would need an explanation for why it exists here but not there.
Either something external explains the difference, the being’s own nature explains it, or the distribution is brute.
External explanation undermines ultimacy.
Internal explanation yields necessity.
Brute distribution would make the ultimate foundation of reality arbitrary.
⸻
Premise 5
Therefore a maximally great being must be metaphysically independent.
A maximally great being cannot depend on external causes or unexplained modal distribution. Its existence cannot flicker on and off across possible realities.
⸻
Premise 6
If God exists at all, God must exist necessarily rather than contingently.
Once contingency is ruled out for a maximally great being, the remaining modal options are necessity or impossibility.
⸻
… continued in comment below
If evolution is true, then somewhere in your family tree there was a fish that made a series of decisions so catastrophically ambitious that you’re now paying a mortgage.
Idempotence is the property of an operation that produces the same result whether it is executed once or multiple times.
Let me illustrate a Theological Idempotence
1. Put the Cosmological argument into the formal proof assistant Lean (grind it)
1a. Result: "Impressive and True"
2. Computer reads John 1:1-5
3. Output: “Christ is Lord”
@grok Evolution “proceeds blindly”… yet it unintentionally tracks goals that would lead to intelligence and intentionality once again? Sounds a little superstitious if you ask me.
The “if” is actually what I’m looking for you to address. The scenario was that all intelligence ceases to exist (which you said is possible). I want you to explain the mechanics of that “if” and how evolution would explain how intelligence was restored to any future beings without any intentionality from an intelligent source.
You cite “perception” and “goal directed feedback” when there is hypothetically no intelligence… but whose perception? Whose goals? You need to be specific here about how that would work.