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A Slingshot from S4 to S5 establishing the Modal Ontological Argument?

…Or why the “strong” atheologian, i.e. the atheologian who holds that there is no omniscient, omnipotent, and omnibenevolent being, must say that ♢Θ semantically entails ☐Θ in S4.

Θ is the proposition that necessarily there is an omniscient, omnipotent, and omnibenevolent being.  

That is:

Kx ≝ x is omniscient
Px ≝ x is omnipotent
Bx ≝ x is omnibenevolent
Θ ≝ ☐(∃x)[(Kx ∧ Px) ∧ Bx]

Consider the following:

1. It is false that ♢Θ semantically entails ☐Θ in S4.

If that is true, then:

2. There is a world in which the valuation of ♢Θ at that world in S4 is true, and the valuation of ☐Θ at that world in S4 is false.

But this is just to say…

3. ♢♢Θ

That is, there is a world in which it is true that ♢Θ.  Moreover, it is an axiom of S4 that ♢♢p → ♢p, and so:

4. ♢Θ

But given our definition for “Θ”, we can say:

5. ♢☐(∃x)[(Kx ∧ Px) ∧ Bx]

Since S5 is just an extension of S4, if something is possible in S4 it is also possible in S5.  Given that ♢☐p → ☐p is an axiom in S5:

6. ☐(∃x)[(Kx ∧ Px) ∧ Bx]

And since ☐p → p in S5 (axiom M/T), we can conclude:

7. (∃x)[(Kx ∧ Px) ∧ Bx]

Hence, the committed “strong” atheologian must say that ♢Θ semantically entails ☐Θ in S4.  Moreover, since S4 is strongly complete, the atheologian is committed to: 

♢Θ ⊢S4 ☐Θ

I’d like to see that deduction. 

[Update]: One objection that I have encountered is that the move from 5 to 6 seems to switch frameworks from S4 to S5, and so the argument is invalid. The argument does not presume S4 as the framework, but rather attempts to exploit an intuition about what is semantically entailed about ♢Θ in S4. In other words, if you grant that such entailment doesn’t hold in S4, I think it follows that you are committed to ♢♢Θ in S4 and S5, which of course is just to say that you are committed to ♢Θ in S5. So from the framework of S5, and its related axioms, you would have to be committed to Θ.

In an attempt to more clearly show how I am not applying axioms of S5 in S4, here is a more formal representation of the argument. Add to our key, the following:

T ≝ true
F ≝ false
V(ω)M(P) = … the valuation at ω in model M of proposition p equals…

1. (∀p)(∀q)~[p ⊨S4 q] → (∃ω){[V(ω)S4(p) = T] ∧ [V(ω)S4(q) = F] (premise)
2. (∃ω){[V(ω)S4(p) = T] ∧ [V(ω)S4(q) = F] → ⊨S4♢p} (premise)
3. (∀p){⊨S4♢p → (∃ω){[V(ω)S5(p) = T]} (premise)
4. (∀p)(∃ω){[V(ω)S5(p) = T] → ⊨S5♢p} (premise)
5. (∀p)[⊨S5♢♢☐p → ⊢S5☐p] (premise)
6. ~[♢Θ ⊨S4 ☐Θ] (premise)
7. (∀q)~[♢Θ ⊨S4 q] → (∃ω){[V(ω)S4(♢Θ) = T] ∧ [V(ω)S4(q) = F] (1 UI)
8. ~[♢Θ ⊨S4 ☐Θ] → (∃ω){[V(ω)S4(♢Θ) = T] ∧ [V(ω)S4(☐Θ) = F] (7 UI)
9. (∃ω){[V(ω)S4(♢Θ) = T] ∧ [V(ω)S4(☐Θ) = F] (6,8 MP)
10. [V(w)S4(♢Θ) = T] ∧ [V(w)S4(☐Θ) = F (9 EI)
11. [V(w)S4(♢Θ) = T] (10 Simp)
12. (∃ω)S4(♢Θ) = T] (11 EG)
13. (∃ω){[V(ω)S4(♢Θ) = T] → ⊨S4♢♢Θ (2 UI)
14. ⊨S4♢♢Θ (12,13 MP)
15. ⊨S4♢♢Θ → (∃ω){[V(ω)S5(♢Θ) = T] (3 UI)
16.(∃ω){[V(ω)S5(♢♢Θ) = T] → ⊨S5♢♢Θ (4 UI)
17. ⊨S4♢♢Θ → ⊨S5♢♢Θ (15,16 HS)
18. ⊨S5♢♢Θ (14,17 MP)
19. ⊨S5♢♢☐(∃x)[(Kx ∧ Px) ∧ Bx] (18 Def “Θ”)
20. ⊨S5♢♢☐(∃x)[(Kx ∧ Px) ∧ Bx] → ⊢S5☐(∃x)[(Kx ∧ Px) ∧ Bx] ∧ Bx] (5 UI)
21. ⊢S5☐(∃x)[(Kx ∧ Px) ∧ Bx] ∧ Bx](19,20 MP)

The Dilemma Once More

P1. If it is possible that necessarily there is an omniscient, omnipotent, omnibenevolent being, necessarily there is an omniscient, omnipotent, omnibenevolent being. (From axiom 5 of S5)[1]

P2. Either the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being” entails the proposition “there is gratuitous evil and suffering” or it is not the case the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being” entails the proposition “there is gratuitous evil and suffering”. (From the Law of the Excluded Middle)[2]

P3. For all propositions p if there is some proposition q such that it is not the case that p entails q, then possibly p. (Contraposition of the Principle of Explosion)[3][4]

C1. If it is not the case the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being” entails the proposition “there is gratuitous evil and suffering”, it is possible that necessarily there is an omniscient, omnipotent, omnibenevolent being. [From P3][5]

C2. If it is not the case the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being” entails the proposition “there is gratuitous evil and suffering”, necessarily there is an omniscient, omnipotent, omnibenevolent being. [From P1 and C1, Hypothetical Syllogism][6]

P4. If the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being” entails the proposition “there is gratuitous evil and suffering”, gratuitous evil and suffering is not counter-evidence to the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being”.[7]

C3. Either necessarily there is an omniscient, omnipotent, omnibenevolent being, or gratuitous evil and suffering is not counter-evidence to the proposition “necessarily there is an omniscient, omnipotent, omnibenevolent being.” (From P2,C2,P4 Constructive Dilemma)[8][9]

[1] The axiom in S5 can be found here: https://en.m.wikipedia.org/wiki/S5_(modal_logic). So, given the axiom 5 of S5: ♢p → ☐♢p

Here is the proof for P1:

Let

Kx ≝ x is omniscient
Px ≝ x is omnipotent
Bx ≝ x is omnibenevolent

1 ~ ☐(∃x)[(Kx ∧ Px) ∧ Bx] (Assump. CP)
2 ~ ☐~~(∃x)[(Kx ∧ Px) ∧ Bx] (1 DN)
3 ♢~(∃x)[(Kx ∧ Px) ∧ Bx] (2 ME)
4 ☐♢~(∃x)[(Kx ∧ Px) ∧ Bx] (3 Axiom 5)
5 ☐~~♢~(∃x)[(Kx ∧ Px) ∧ Bx] (4 DN)
6 ☐~☐(∃x)[(Kx ∧ Px) ∧ Bx] (5 ME)
7 ~☐(∃x)[(Kx ∧ Px) ∧ Bx] → ☐~☐(∃x)[(Kx ∧ Px) ∧ Bx] (CP 1-6)
8 ~☐~☐(∃x)[(Kx ∧ Px) ∧ Bx] → ~~☐(∃x)[(Kx ∧ Px) ∧ Bx] (7 Contra)
9 ~☐~☐(∃x)[(Kx ∧ Px) ∧ Bx] → ☐(∃x)[(Kx ∧ Px) ∧ Bx] (8 DN)
10 ♢☐(∃x)[(Kx ∧ Px) ∧ Bx] → ☐(∃x)[(Kx ∧ Px) ∧ Bx] (9 ME)

[2] The Law of the Excluded Middle can be found here: https://en.m.wikipedia.org/wiki/Law_of_excluded_middle

[3] Contraposition can be found here: https://en.m.wikipedia.org/wiki/Contraposition

[4] The Principle of Explosion can be found here: https://en.m.wikipedia.org/wiki/Principle_of_explosion

Here is the proof that P3 is the contrapositive of the Principle of Explosion, which we will state as follows: (∀p)[~♢p → (∀q)(p ⊨ q)], for all propositions p, if p is impossible, then for all propositions q1, p entails q.

1 (∀p)[~♢p → (∀q)(p ⊨ q)] (Principle of Explosion)
2 ~♢φ → (∀q)(φ ⊨ q) (1 UI)
3 ~(∀q)(φ ⊨ q) → ~~♢φ (2 Contra)
4 (∃q)~(φ ⊨ q) → ~~♢φ (3 QN)
5 (∃q)~(φ ⊨ q) → ♢φ (4 DN)
6 (∀p)(∃q)~(p ⊨ q) → ♢p] (5 UG)

[5] Here is the proof that C1 follows from P3:

Let

G ≝ ☐(∃x)[(Kx ∧ Px) ∧ Bx]
E ≝ ‘there is gratuitous evil and suffering’

1 (∀p)(∃q)~(p ⊨ q) → ♢p] (P3)
2 ~(G ⊨ E) (Astump. CP)
3 (∃q)~(G ⊨ q) → ♢G (1 UI)
4 (∃q)~(G ⊨ q) (2 EG)
5 ♢G (3,4 MP)
6 ~(G ⊨ E) → ♢G (205 CP)
7 ~(G ⊨ E) → ♢☐(∃x)[(Kx ∧ Px) ∧ Bx] (6 def. of ‘G’)

Thus Line 7 (C1) follows from Line 1 (P3), QED.

[6] Hypothetical Syllogism can be found here: https://en.m.wikipedia.org/wiki/Hypothetical_syllogism

[7] This premise is defended on given a Bayesian interpretation of counter-evidence:
(∀p)(∀q){[P(p|q)<P(p)] ⊃ Cqp} (read as: for all proposition p and q, if the probability of q given p is less than the probability of q unconditioned, then q is counter-evidence for p).

If we assume G ⊨ E, then by Logical Consequence P(E|G) = 1, but if E is counter-evidence to G, then it must be the case that P(G|E) < P(G). But both of these statements about probabilities cannot be true.

According to Bayes’ Theorem:

P(E|G) = [P(E)/P(G)] x P(G|E)

So given P(E|G) = 1

We can infer:

P(G)/P(G|E) = P(E)

But given 0 ≤ P(E) ≤ 1, it is not possible for P(G)/P(G|E) = P(E) and P(G|E) < P(G), as whenever the denominator is less than the numerator, the result is greater than 1.

Hence, we must reject the assumption that [P(E|G) = 1] ∧ [P(G|E) < P(G)]. This provides us with the following defense of P4:

1 ~{[P(E|G) = 1] ∧ [P(G|E) < P(G)]} (Result from the proof by contradiction above)
2 ~[P(E|G) = 1] ∨ ~[P(G|E) < P(G)] (1 DeM)
3 [P(E|G) = 1] → ~[P(G|E) < P(G)] (2 Impl)
4 [G ⊨ E] → [P(E|G) = 1] (by Logical Consequence)
5 [G ⊨ E] → ~[P(G|E) < P(G)] (3,4 HS)

And line 5 is just what is meant by P4.

[8] Constructive Dilemma can be found here: https://en.m.wikipedia.org/wiki/Constructive_dilemma

[9] The proof of the entire argument is as follows:

1 ♢☐(∃x)[(Kx ∧ Px) ∧ Bx] → ☐(∃x)[(Kx ∧ Px) ∧ Bx] (Premise)
2 (G ⊨ E) ∨ ~(G ⊨ E) (Premise)
3 (∀p)(∃q)~(p ⊨ q) → ♢p] (Premise)
4 [G ⊨ E] → ~[P(G|E) < P(G)] (Premise)
5 ~(G ⊨ E) (Assump CP)
6 (∃q)~(G ⊨ q) → ♢G (3 UI)
7 (∃q)~(G ⊨ q) (5 EG)
8 ♢G (6,7 MP)
9 ~(G ⊨ E) → ♢G (5-8 CP)
10 ~(G ⊨ E) → ♢☐(∃x)[(Kx ∧ Px) ∧ Bx] (9 definition of ‘G’)
11 ~(G ⊨ E) → ☐(∃x)[(Kx ∧ Px) ∧ Bx] (1,10 HS)
12 ☐(∃x)[(Kx ∧ Px) ∧ Bx] ∨ ~[P(G|E) < P(G)] (2,4,11 CD)

The Dilemma Theodicy

  1. By definition, God is a maximally great being, i.e. an omnipotent, omniscience, morally perfect being in every possible world.
  2. Any argument against God’s existence that depends on a premise of the form “If God were to exist, then we would expect there to be x” (hereafter, the “counterfactual” premise) must have a justification, either by way of a trivial entailment, given the incoherence of the concept of God, and so the impossibility of the existence of God, or by way of the defense of a substantive counterfactual implication, given a thoroughgoing conceptual analysis of the concept of God, and the sorts of states of affairs implied by God’s existence.
  3. If the justification for the “counterfactual” premise is by way of a trivial entailment, given the incoherence of the concept of God, and so the impossibility of the existence of God, then the justification for the “counterfactual” premise begs the question of any argument against God’s existence that depends upon the “counterfactual” premise, which means the argument containing the “counterfactual” premise is informally fallacious.
  4. If the justification for the “counterfactual” premise is by way of a defense of a substantive counterfactual implication, given a thoroughgoing conceptual analysis of the concept of God, and the sorts of states of affairs implied by God’s existence, then the justification depends upon the metaphysical possibility of God, and the sorts of states of affairs that obtain in the nearest possible worlds where God exists, which also serves as a justification for the possibility premise of the modal ontological argument, by which the existence of God can be directly demonstrated from His metaphysical possibility, based upon an axiom of S5.
  5. But, a successful argument cannot be informally fallacious, nor can a successful argument depend on a justification that directly implies the contradictory of the its conclusion.
  6. So, no argument against God’s existence that depends on the “counterfactual” premise is successful.

Escaping the horns would require a substantive justification of the counterfactual premise that does not imply any real metaphysical possibility of God.  Would such a justification be compelling enough for a theist, or neutral party to accept the truth of the counterfactual premise? 

A Formal Version of the Third Way

I believe by using mereological sums, I avoid the charge of the quantifier shift fallacy.

D1: God is the x such there is not some y by which x receives the necessity it has, and x is a member of the essentially ordered causal series by which things receive their necessity .
P1. For all x, if it is possible that x does not exist, then there is a time at which x does not exist.
P2. If there is a time at which the mereological sum of everything does not exist, then there does not exist now the mereological sum of everything.
P3. If there exists now some x, then there exists now the mereological sum of everything.
P4. I exist now.
P5. If necessarily there exists the mereological sum of everything, then there is some x that necessarily exists, and x is a part of the mereological sum of everything.
P6. If there is some x that necessarily exists, then if for all x, x necessarily exists, then there is some y such that x receives the necessity it has from y, only if there is an essentially ordered causal series by which things receive their necessity and it does not regress finitely.
P7. For all z it is not the case that there is an x, such that both x is a member of the essentially ordered causal series by which things receive z and it is not the case that z regresses finitely.
P8. For all x, if x necessarily exists, then x is a member of the essentially ordered causal series by which things receive their necessity.
P9. For all x, if there is not some y by which  x receives the necessity it has, and x is a member of the essentially ordered causal series by which things receive their necessity, then for all z, there is not some y by which z receives the necessity it has, and z is a member of the essentially ordered series by which things receive their necessity, and z is identical to x.
C1. God necessarily exists.

Note: D1 tells us that God does not receive his necessity from any other cause, but, being a part of the causal series by which things receive their necessity, is the cause of necessity in other things.

Let:
E!x ≝ x exists
E!t ≝ x exists at time t
Fx ≝ x regresses finitely
Oxy ≝ x is a member of essentially ordered causal series y
Rxy ≝ x receives the necessity it has from y
σ<x,P> ≝ the mereological sum of all x that P.
σ<e,E!> ≝ (∀x)[E!x ⊃ (x ≤ e)] & (∀y)[(y ≤ e) ⊃ (∃z)(E!z & (y ⊗ z)]1
e ≝ everything
g ≝ (ɿx)[~(∃y)Rxy & Oxl]
i ≝ I (the person who is me)
l ≝ the causal series by which things receive their necessity
n ≝ now

1. (∀x)[♢~E!x ⊃ (∃t)~E!tx] (premise)
2. (∃t)~E!tσ<e,E!> ⊃ ~E!nσ<e,E!> (premise)
3. (∃x)E!nx ⊃ E!nσ<e,E!>(premise)
4. E!ni (premise)
5. ☐E!σ<e,E!> ⊃ (∃x)[☐E!x &(x ≤ e)] (premise)
6. (∃x)☐E!x ⊃ {(∀x)[☐E!x ⊃ (∃y)Rxy] ⊃ (∃x)[Oxl & ~Fl]} (premise)
7. (∀z)~(∃x)[Oxz & ~Fz] (premise)
8. (∀x)[☐E!x ⊃ Oxl] (premise)
9. (∀x){[~(∃y)Rxy & (Oxl & Fl)] ⊃ (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = x)]} (premise)
10. ♢~E!σ<e,E!> (IP)
11. ♢~E!σ<e,E!> ⊃ (∃t)~E!tσ<e,E!> (1 UI)
12. (∃t)~E!tσ<e,E!> (10,11 MP)
13. ~E!nσ<e,E!> (2,12 MP)
14. (∃x)E!nx (4 EG)
15. E!nσ<e,E!> (3,14 MP)
16. E!nσ<e,E!> & ~E!nσ<e,E!> (13,15 Conj)
17. ~♢~E!σ<e,E!> (10-16 IP)
18. ☐E!σ<e,E!> (17 ME)
19. (∃x)[☐E!x &(x ≤ e)] (5,18 MP)
20. ☐E!μ & (μ ≤ e) (19 EI)
21. ☐E!μ (20 Simp)
22. (∃x)☐E!x (21 EG)
23. (∀x)[☐E!x ⊃ (∃y)Rxy] ⊃ (∃x)[Oxl & ~Fl] (6,22 MP)
24. ~(∃x)(Oxl & ~Fl)] (7 UI)
25. ~(∀x)[☐E!x ⊃ (∃y)Rxy] (23,24 MT
26. (∃x)~[☐E!x ⊃ (∃y)Rxy] (25 QN)
27. (∃x)~[~☐E!x ∨ (∃y)Rxy] (26 Impl)
28. (∃x)[~~☐E!x & ~(∃y)Rxy] (27 DeM)
29. ~~☐E!ν & ~(∃y)Rνy (28 EI)
30. ☐E!ν & ~(∃y)Rνy (29 DN)
31. ☐E!ν (30 Simp)
32. ☐E!ν ⊃ Oνl (8 UI)
33. Oνl (31,32 MP)
34. ~(∃x)[Oxl & ~Fl] (7 UI)
35. (∀x)~[Oxl & ~Fl] (34 QN)
36. ~[Oνl & ~Fl] (35 UI)
37. ~Oνl ∨ ~~Fl (36 DeM)
38. ~~Oνl (33 DN)
39. ~~Fl (37,38 DS)
40. Fl (39 DN)
41. ~(∃y)Rνy (30 Simp)
42. Oνl & Fl (33,40 Conj)
43. ~(∃y)Rνy (Oνl & Fl) (41,42 Conj)
44. [~(∃y)Rνy & (Oνl & Fl)] ⊃ (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = ν)] (9 UI)
45. (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = ν)] (43,44 MP)
46. ~(∃y)Rνy & Oνl (33,41 Conj)
47. [~(∃y)Rνy & Oνl] & (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = ν)] (45,46 Conj)
48. [~(∃y)Rνy & Oνl] & (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = ν)] & ☐E!ν (31,47 Conj)
49. (∃x){[~(∃y)Rxy & Oxl] & (∀z)[(~(∃y)Rzy & Ozl) ⊃ (z = x)] & ☐E!x} (48 EG)
50. ☐E!g (49 Theory of Descriptions)

QED

1Formulation of definition for everything based influenced by Filip, H. (n.d.) “Mereology”. Online: https://user.phil-fak.uni-duesseldorf.de/~filip/Mereology.pdf

A Modest Formulation of the Ontological Argument

In this post, I have formulated Anselm’s argument for the necessary existence of a being than which none greater can be conceived.  However, I have noted that the argument depends upon a two-place “greater than” predicate that functions with something like the Neo-Platonic “Great Chain of Being” in mind.  Some thing, x, is conceived to be greater than y in the sense that x is understood to have more capacities or has an essence that can be actualized to a greater degree. For example, a plant is understood to contingently exists, grows, takes in nutrients, and reproduces. An animal is understood to be greater in the sense that it too contingently exists, grows, takes in nutrients, and reproduces, but it also has capacities like sentience, and can self-move, etc. So the greater something is, the more powers/more capacities it is understood to have. If God exists, then God would be that being which none more powerful could be conceived, which is just to say “none greater”. I find the metaphysics where a two-place “conceivably greater than” predicate can be objectively exemplified to be extremely plausible. There is an objective sense in which I have greater capacities and abilities than a flea.

The argument is as follows:

D1. Some x is an Anselmian God if and only if x is conceivable, it is not the case that there is something that is conceivably greater than x, and x necessarily exists.

P1. There is some x conceivable such that there is nothing conceivably greater than x.

P2. For all x, if the possibility of failing to conceive of x implies the possibility that x doesn’t exist, x is mentally dependent (premise).

P3. For all x, if x is mentally dependent, there is some y such that y is conceivably greater than x (premise).

P4. If there is some x such that necessarily there is some z and z is identical to x, and x is an Anselmian God, then necessarily there exists an Anselmian God.

Therefore,

C1. Necessarily, there is an Anselmian God.

That is the argument in ordinary language. To show that it is a formally valid syllogism, I offer the following formal deduction:

Let,

Cx ≝ x is conceived
Mx ≝ x is mentally dependent
Gxy ≝ x is conceived to be greater than y
Θx ≝ (∃x){[♢Cx & ~(∃y)♢Gyx]& ☐(∃z)(z=x)} (Def Θx)

1. (∃x)[♢Cx & ~(∃y)♢Gyx] (premise)
2. (∀x){[♢~Cx ⊃ ♢~(∃z)(z=x)] ⊃ Mx} (premise)
3. (∀x)[Mx ⊃ (∃y)♢Gyx] (premise)
4. (∃x)[☐(∃z)(z=x)& Θx] ⊃ ☐(∃x)Θx (premise)
5. (∀x){[♢Cx & ~(∃y)♢Gyx] ⊃ [♢~Cx ⊃ ♢~(∃z)(z=x)]} (IP)
6. ♢Cμ & ~(∃y)♢Gyμ (1 EI)
7. [♢~Cμ ⊃ ♢~(∃z)(z=μ)] ⊃ Mμ (2 UI)
8. Mμ ⊃ (∃y)(♢Gyμ) (3 UI)
9. [♢~Cμ ⊃ ♢~(∃z)(z=μ)] ⊃ (♢Gyμ)(7,8 HS)
10. ♢Cμ & ~(∃y)♢Gyμ] ⊃ [♢~Cμ ⊃ ♢~(∃z)(z=μ)] (5 UI)
11. ♢~Cμ ⊃ ♢~(∃z)(z=μ) (6,10 MP)
12. (∃y)♢Gyμ (7,9 MP)
13. ♢Gνμ (12 EI)
14. ~(∃y)♢Gyμ (6 Simp)
15. (∀y)~(♢Gyμ) (14 QN)
16. ~♢Gνμ (15 UI)
17. ♢Gνμ & ~♢Gνμ (13,16 Conj)
18. ~(∀x){[♢Cx & ~(∃y)♢Gyx] ⊃ [♢~Cx ⊃ ♢~(∃z)(z=x)]} (5-17 IP)
19. (∃x)~{[♢Cx & ~(∃y)♢Gyx] ⊃ [♢~Cx ⊃ ♢~(∃z)(z=x)]} (18 QN)
20. (∃x) ~{~[♢Cx & ~(∃y)♢Gyx] ∨ [♢~Cx ⊃ ♢~(∃z)(z=x)]} (19 Impl)
21. (∃x){~~[♢Cx & ~(∃y)♢Gyx] & ~[♢~Cx ⊃ ♢~(∃z)(z=x)]} (20 DeM)
22. (∃x){[♢Cx & ~(∃y)♢Gyx] & ~[♢~Cx ⊃ ♢~(∃z)(z=x)]} (21 DN)
23. (∃x){[♢Cx & ~(∃y)♢Gyx] & ~[~♢~Cx ∨ ♢~(∃z)(z=x)]} (22 Impl)
24. (∃x){[♢Cx & ~(∃y)♢Gyx] & ~[☐Cx ∨ ♢~(∃z)(z=x)]} (23 ME)
25. (∃x){[♢Cx & ~(∃y)♢Gyx] & [~☐Cx & ~♢~(∃z)(z=x)]} (24 DeM)
26. (∃x){[♢Cx & ~(∃y)♢Gyx] & [~☐Cx & ☐(∃z)(z=x)]} (25 ME)
27. [♢Cμ & ~(∃y)♢Gyμ] & [~☐Cμ & ☐(∃z)(z=μ)] (26 EI)
28. ~☐Cμ & ☐(∃z)(z=μ) (27 Simp)
29. ☐(∃z)(z=μ) (28 Simp)
30. [♢Cμ & ~(∃y)♢Gyμ] (27 Simp)
31. [♢Cμ & ~(∃y)♢Gyμ] & ☐(∃z)(z=μ) (29,30 Conj)
32. Θμ (31 Def “Θx”)
33. ☐(∃z)(z=μ) & Θμ (29,32 Conj)
34 (∃x)[☐(∃z)(z=x) & Θx] (33 EG)
35. ☐(∃x)Θx (4,34 MP)

QED

Indeed, I find the above argument very persuasive. However, there may be some who are resistant to the notion that the two-place “conceivably greater-than” predicate can actually and objectively be exemplified. For such a person, I propose a more modest version of the argument. The more modest version is that, since C1, i.e. “☐(∃x)Θx”, is provable given P1-P4,one can argue that if P1-P4 are jointly possible, C1 is possible, and so an Anselmian God necessarily exists. This follows given S5 in modal logic, which says that ◊☐P entails ☐P. The argument can be formally proved as follows:

Let, also:

P1 ≝ (∃x)[♢Cx & ~(∃y)♢Gyx]
P2 ≝ (∀x){[♢~Cx ⊃ ♢~(∃z)(z=x)] ⊃ Mx}
P3 ≝ (∀x)[Mx ⊃ (∃y)♢Gyx]
P4 ≝ (∃x)[☐(∃z)(z=x) & Θx] ⊃ ☐(∃x)Θx
C1 ≝ ☐(∃x)Θx

36. ◊[(P1 & P2) & (P3 & P4)] (premise)
37. [(P1 & P2) & (P3 & P4)] ⊢ C1 (premise; proved by 1-35)
38. [◊[(P1 & P2) & (P3 & P4)]& {[(P1 & P2) & (P3 & P4)]⊢ C1}] ⊃ ◊C1 (premise)
39. ◊[(P1 & P2) & (P3 & P4)] & {[(P1 & P2) & (P3 & P4)] ⊢ C1} (36,37 Conj)
40. ◊C1 (38,39 MP)
41. ◊☐(∃x)Θx (40 Def “C1”)
42. ☐(∃x)Θx (41 by “S5”)

QED (again)

Since (37) is established, and (38) merely argues that if premises are jointly possible, and those premises prove some conclusion, then the conclusion is possible, (38) is relatively uncontroversial.  So, if one objects that P1-P4 are not actually true, but admits that they are at least broadly logically, or metaphysically compossible, then one ought to agree that, necessarily, an Anselmian God exists.

Some Proposed Corrections to Maydole’s Temporal Contingency Argument

Robert Maydole presents an interesting argument for a supreme being, called the temporal contingency argument.  The argument is a long deduction, and so is seen as somewhat difficult to comprehend. The version that I am critiquing appears in the Blackwell Companion to Natural Theology and appears as follows (with highlighted lines that I believe are problematic)[1]:

Maydole-TCA3

These errors are not fatal to the argument, however.  Here is a quick workaround that I think preserves the spirit of Maydole’s deduction (using nested conditional proofs and the identity rule, for example).  I’ve simplified some of the lexicon, but if pretty much follows Maydole’s definitions.  A revised deduction is as follows:

Bx ≝ x begins to exist at some time and ceases to exist at some time
Tx ≝ x is temporally necessary
Cx ≝ x is temporally-contingent
Fx ≝ x exists for a finite period of time
≝ Only finitely many things have existed to date
≝ Something presently exists
≝ There was a time when nothing existed
Sxy ≝ x is a sufficient reason for the existence of y
Wx ≝ x is without any limitations
Gxy ≝ x is greater than y
Sx ≝ (~◊(∃y)Gyx & ~◊(∃y)(x≠y & ~Gxy))
 
Deduction

1. P (premise)
2. M (premise)
3. (
∀x)(Cx ⊃ Bx) (premise)
4. (∀x)(Bx ⊃ Fx) (premise)
5. ((∀x)Fx & M) ⊃ N (premise)
6. N ⊃ ~P (premise)
7. (
∀x)(Tx ≡ ~Cx) (premise)
8. (∀x)Cx (IP)
9. Cμ ⊃ Bμ (3 UI)
10. Cμ (8 UI)
11. B
μ (9,10 MP)
12. B
μ ⊃ Fμ (4 UI)
13. Fμ (11,12 MP)
14. (∀x)Fx (13 UG)
15. (∀x)Fx & M (2,14 Conj)
16. N (5,15 MP)
17 ~P (6,16 MP)
18. P & ~P (1,17 Conj)
19. ~(
∀x)Cx (8–18 IP)
20. (∃x)~Cx (19 QN)
21. ~Cν (20 EI)
22. Tν ≡ ~Cν (7 UI)
23. (T
ν ⊃ ~Cν) & (~Cν ⊃ Tν) (22 Equiv)
24. (~C
ν ⊃ Tν) (23 Simp)
25. Tν (21,24 MP)
26. (∃x)Tx (25 EG)
27. (
∀x)(∃y)Syx (premise)
28. (∀x)[(∃y)Syx ⊃ (∃z)(Szx & Szz)] (premise)
29. (∀x)(∀y)[(Tx & Syx) ⊃ ~Cy] (premise)
30. (∀y)[(Ty & Syy) ⊃ Wy] (premise)
31. (∀y)[Wy ⊃ ☐(∀z)(z≠y ⊃ Gyz)] (premise)
32. ~◊(∃y)Gyy (premise)
33. 
☐(∀x)(∀y)(Gxy ⊃ ~Gyx) (premise)
34. (∃y)Syν (27 UI)
35. (∃y)Syν ⊃ (∃z)(Szν & Szz) (28 UI)
36. (∃z)(Szν & Szz) (34,35 MP)
37. Suν & Suu (36 EI)
38. (∀y)[(Tν & Syν) ⊃ ~Cy] (29 UI)
39. (Tν & Suν) ⊃ ~Cu (38 UI)
40. Suν (37 Simp)
41. Tν & Suν (25,40 Conj)
42. ~Cu (39,41 MP)
43. Tu ≡ ~Cu
 (7 UI)
44. (Tu ⊃ ~Cu) & (~Cu ⊃ Tu) (43 Equiv)
45. ~Cu ⊃ Tu (44 Simp)
46. Tu (42,45 MP)
47. Suu (37 Simp)
48. Tu & Suu (46,47 Conj)
49. (Tu & Suu) ⊃ Wu (30 UI)
50. Wu ⊃ 
☐(∀z)(z≠u ⊃ Guz) (31 UI)
51. Wu (48,49 MP)
52. ☐(∀z)(z≠u ⊃ Guz) (50,51 MP)
53. ☐(∀z)(~z≠u ∨ Guz) (52 Impl)
54. ☐(∀z)(~z≠u ∨ ~~Guz) (53 DN)
55. ☐(∀z)~(z≠u & ~Guz) (54 DeM)
56. ☐~(∃z)(z≠u & ~Guz) (55 QN)
57. ~◊(∃z)(z≠u & ~Guz) (56 MN)
58. 
☐~(∃y)Gyy (32 MN)
59. ☐(∀y)~Gyy (58 QN)
60. (∀y)~Gyy (CP)
61. μ=ν (CP)
62. ~Gμμ (60 UI)
63. ~Gμν (61,62 IR)
64. μ=ν ⊃ ~Gμν (61-63 CP)
65. (∀y)~Gyy ⊃ (μ=ν ⊃ ~Gμν) (60-64 CP)
66. ☐[(∀y)~Gyy ⊃ (μ=ν ⊃ ~Gμν)] (65 NI)
67. ☐(μ=ν ⊃ ~Gμν) (59,66 MMP)
68. ☐(∀x)(∀y)(Gxy ⊃ ~Gyx) & ☐(∀z)(z≠ν ⊃ Gνz) (33,52 Conj)
69. [☐(∀x)(∀y)(Gxy ⊃ ~Gyx) & ☐(∀z)(z≠ν ⊃ Gνz)] ⊃ ☐[(∀x)(∀y)(Gxy ⊃ ~Gyx) & (∀z)(z≠ν ⊃ Gνz)] (theorem)
70. ☐[(∀x)(∀y)(Gxy ⊃ ~Gyx) & (∀z)(z≠ν ⊃ Gνz)] (68,69 MP)
71. {[(∀x)(∀y)(Gxy ⊃ ~Gyx) & (∀z)(z≠ν ⊃ Gvz)] ⊃ (μ≠ν ⊃ ~Gμν)} (theorem)
72. ☐(μ≠ν ⊃ ~Gμν) (70,71 MMP)
73. [☐(μ=ν ⊃ ~Gμν) & ☐(μ≠ν ⊃ ~Gμν)] ⊃ ☐[(μ=ν ∨ μ≠ν) ⊃ (~Gμν ∨ ~Gμν)] (theorem)
74. ☐(μ=ν ⊃ ~Gμν) & ☐(μ≠ν ⊃ ~Gμν) (67,72 Conj)
75. ☐[(μ=ν ∨ μ≠ν) ⊃ (~Gμν ∨ ~Gμν)] (73,74 MP)
76. ☐(μ=ν ∨ μ≠ν) (theorem)
77. ☐(~Gμν ∨ ~Gμν) (75,76 MMP)
78. ☐(~Gμν ∨ ~Gμν) ⊃ ☐~Gμν (theorem)
79. ☐~Gμν (77,78 MP)
80. (∀z)☐~Gzν (79 UG)
81. (∀z)☐~Gzν ⊃ ☐(∀z)~Gzν (theorem)
82. ☐(∀z)~Gzν (80,81 MP)
83. ☐~(∃z)Gzν (82 QN)
84. ~◊(∃z)Gzν (83 MN)
85. ~◊(∃z)Gzν & ~◊(∃z)(z≠ν & ~Gνz) (57,84 Conj)
86. Sν (85 def “S”)
87. (∃x)Sx (86 EG)

[1]R. Maydole. 2012. “The Ontological Argument”. The Blackwell Companion to Natural Theology. Ed. W.L. Craig & J.P. Moreland. Malden, MA: Blackwell Publishing. Document image retrieved from <http://commonsenseatheism.com/wp-content/uploads/2009/05/irrefutable.png>.

A Voltairean Argument for God’s Existence

This post is a variation on what I have called an indispensability argument.  My original formulation can be found here, and I have made some further comments here. In this post, I thought I would do a take on the argument using Voltaire’s famous dictum “Si Dieu n’existait pas, il faudrait l’inventer” as an explicit premise (Epistle to the author of the book, The Three Impostors, 1768).  As an aside, it is commonly supposed that, since Voltaire was critical of organized religion, he was an atheist.  Voltaire was a deist. In fact, in the poem where he says that if God does not exist, it would be necessary to invent him, Voltaire doesn’t merely refer to God as some generic super-being, but as the “supreme essence.”  So it seems that he has something like a perfect being, or the God of the philosophers, in mind, at least in this poem.  I find the following argument cogent, and I think historical reflection makes the premises plausible. Thoughts are always appreciated, of course, though I anticipate some objections below.

  1. If God does not actually exist, it is necessary to invent the concept of God. [Voltairean Premise]
  2. For all x, if it is necessary to invent the concept of x, the concept of x is logically coherent. [Premise]
  3. If the concept of God is logically coherent, God actually exists. [By S5 and the logical possibility of God as a perfect being is necessarily existent and essentially perfect]
  4. For all x, x does not actually exist, or x actually exists. [Law of the Excluded Middle]

Therefore, God actually exists. Proof:

  1. Either God actually exists, or it is necessary to invent the concept of God. [From 1 Material Implication]
  2. If it is necessary to invent the concept of God, the concept of God is logically coherent. [From 2 Universal Instantiation]
  3. If it is necessary to invent the concept of God, God actually exists. [From 3, 6 Hypothetical Syllogism]
  4. God does not actually exist, or God actually exists. [From 4 Universal Instantiation]
  5. If God actually exists, God actually exists. [From 8 Material Implication]
  6. Either God actually exist, or God actually exists. [From 5, 7, and 9 Constructive Dilemma]
  7. God actually exists. [From 10 Tautology]

In this argument, I want to grant the Voltairean Premise, though I suspect most atheists would attack it with a Laplacean counter that “I have no need for that hypothesis.” Indeed, Laplace did not have a need to invoke God to explain the motion of the planets, but I don’t think that was Voltaire’s point. Rather, he was talking about the need of the concept of God for social cohesion. But, I think the concept of God plays a larger role than merely grounding natural law for a social contract, or putting the fear of hellfire into the hearts of the criminally minded and depraved. There is a necessity of God in many aspects of philosophical speculation. It is out of the concept of God that various philosophical concepts found further development, such as the notions of free will, personhood, simplicity, and aseity. The concept of God has helped thinkers clarify concepts surrounding Being, substance, essence, the relationship between eternality and time, etc. I suspect that the concept of God, a perfect being, was necessary in the intellectual development of our civilization. Whether one thinks that God is currently necessary to ground human rights and dignity, natural law, it happened that way historically. So it is important to note that the concept of this God, the God of the philosophers, is one that is both maximally great and fecund.

If the concept of God, a perfect being, is incoherent then such a history would be surprising, since incoherent concepts are not really all that necessary for anything. I take a concept to be incoherent if the sense of the concept is implicitly contradictory. Such a concept would not be any more necessary for deriving other philosophically interesting concepts than any other incoherent concept. For, impossibilities trivially imply anything and everything. Nonetheless, real work and reflection has gone into inferring the attributes and implications of the God of the philosophers. It is true that theologians and philosophers have come to contrary conclusions from the concept of God, but the steps by which they reach those contrary conclusions are comprehensible and not merely based on an explicit use of the principle of explosion or by being arbitrary. Often times the dispute is based on one philosopher taking an attribute or the concept of perfection to have a different sense than what another philosopher thinks. They genuinely disagree. So, it is not the case that they are simply picking out contradictions—contradictions that they would bashfully agree are there within the concept of God all along— and reaching contrary conclusions. They are actually disagreeing on basic definitions of terms that they think are implied by perfection. That being said, there is some consensus that has grown around perfect being theology. For instance, God’s power does not imply the ability to do the logically impossible, and God cannot make free-agents always do what is morally right. There are still genuine disputes over the details of a maximally great being, or a perfect being, but few would dispute that such a being would be necessary, omnipotent, omniscient, and morally perfect. Some dispute whether God’s omniscience is propositional. For instance, if God is absolutely simple, there can be no composition in God’s knowledge, and so it cannot be based on the composition of subject terms and predicates in the mind of God. But these sorts of disputes are not willy-nilly where anything goes. The disputes are rigorous, and based on careful definitions. So, it seems to me that while the concept of God is not settled upon by all philosophers, there are definite rules around how to do natural theology, and limits upon what the God concept entails.

One might also argue that, though the concept of God, the God of the philosophers, is incoherent, various aspects of the concept are coherent, and it is those aspects that have been fecund in the history of philosophy.  This doesn’t seem to be the case, however.  Rather, it is typically the confluence of various divine attributes that have generated so many ideas.  Perhaps even more to the point, if classical theism and absolute divine simplicity are granted, then these philosophers are not really considering a confluence of God’s attributes, but one essence that reveals itself to us an a variety of ways.  That thought itself has produced some of the most penetrating theology in Judaism, Christianity, and Islam.  The entire Summa Theologiae is built upon this foundation, brick by syllogistic brick.  Perhaps that brick was all straw, but the Summa itself has produced entire schools of philosophy and theology. I think the concept of God was a historical necessity and philosophical necessity, one born out of a reflection on the divine, the perfect, and the infinite. That this concept is both necessary and incoherent would be surprising since, as I have said, any incoherent concept could do the job of generating random inferences.  I don’t think that is what the concept of God has been doing in our history.  I don’t think it is there as an incoherency from which surprising and profound thoughts emerge.  The concept of God gives us traction in a way that a round-square does not.  Round-squares or squared-circles might in some sense be “meaningful” concepts, but they are not necessary to invent.  In fact, it is not entirely clear that they are concepts, at least in the sense that they can be conceived in the mind.  It seems more the case that one is conceiving of roundness and squareness and noting that they cannot be predicated of the same Euclidean plane figure.  They are more an oddity, a conceptual contradiction.  Their use is merely as a stand-in for any obvious instance of an impossibility.

As for premises (3) and (4), they are relatively uncontroversial rules of logic, and I will not go into defending them here. I know some people lament S5, but the issue is not whether the axiom is true, but rather, whether we genuinely know whether something is logically possible rather than, say, merely epistemically possible. I think my defense of (2) makes it clear that I am not merely saying that the God concept is conceivable, but that it contains no incoherency in it. So, I think that if Voltaire’s dictum is right, and the necessity of a concept implies its coherence, we have good reason to think God actually does exist.

SEP update on Medieval Theories of Modality

There have been some important updates to the SEP entry “Medieval Theories of Modality” by Simo Knuuttila. Here is an excerpt pertaining to my interests in the contemporary analysis of Aristotle:

There are several recent works on Aristotle’s modal syllogistics, but no generally accepted historical reconstruction which would make it a coherent theory. It was apparently based on various assumptions which were not fully compatible (Hintikka 1973, Striker 2009). Some commentators have been interested in finding coherent layers of the theory by explicating them in terms of Aristotle’s other views (van Rijen 1989; Patterson 1995). There are also several formal reconstructions such as Rini 2010 (modern predicate logic), Ebert and Nortmann 2007 (possible worlds semantics), various set-theoretical approaches discussed in Johnson 2004, and Malink 2006 (mereological semantics).

I’m going to take a closer look at Striker’s position, as I am not convinced that Aristotle’s modal syllogistic is based on assumptions that are “not fully compatible”. I think the issue is one of getting clear on Aristotle’s metaphysics at the time that the Prior Analytics were composed, and to realize that some of those metaphysical presuppositions did not remain constant as Aristotle went on to work on De Caelo and Metaphysics. I like Malink’s approach of using the Topics in order to understand what is going on. Perhaps a post or two dedicated to the “Two Barbaras” problem is in order!

Revised Meta Modal Ontological Argument in QML

Several weeks ago I posted an ontological argument that I had hoped would overcome many of the powerful parody objections employed against the various Hartshorne-Malcolm-Plantinga modal arguments.  Unfortunately, when I tried to symbolize it, an error became quite obvious.  The lesson is that I should symbolize the arguments before posting them.  This new version essentially reaches the same conclusion I had sought, but it makes use of a two-place predicate.  It’s a simple solution, but the results are quite compelling, at least as far as I can tell (I look forward to potential criticisms).

But before I delve into the argument, I would like to address a worry recently raised on an excellent blog, Third Millennial Templar (the post is linked here).  The concern is whether this argument somehow confuses or conflates epistemic possibility with the relevant modal possibility (metaphysical or broad-logical) needed in a modal ontological argument.  And this worry is well-founded.  After all, the motivation behind (1) is based upon Graham Oppy’s admission that it is an open question whether there is a sound ontological argument that is yet to be found.  In other words, it is at least an epistemic possibility that a sound ontological argument exists.

Nonetheless, I don’t think that this meta modal argument conflates epistemic possibility with other modal possibilities.  Rather, it makes use of epistemic possibility as only part of the background justification for (1).  The rest of the justification comes from the fact that while assertions bear an onus, an epistemic possibility receives the benefit of the doubt for being logically possible.  It would be ruinous to our modal epistemology if we demand positive proof for every logical possibility.  Therefore, we default to the position that something is logically possible unless and until it can be shown to be impossible.  The onus is on the one claiming impossibility, as that is the stronger claim.  The problem with earlier versions of the ontological argument is that, while granting logical possibility to God leads to the conclusion that God exists, maintaining the proof commits one to special pleading so as to not permit the logical possibility that God does not exist.  The benefit of the doubt must be granted to both the existence and non-existence of something, unless there are independent reasons to think that thing is necessary or impossible.  Granting both possibilities to God results in a symmetrical anti-ontological argument that just as easily disproves God’s existence.  Consequently, there is no reason to prefer the conclusion of the ontological argument to that of the anti-ontological argument from reason alone.  So to claim that these earlier ontological arguments serve as disproof for their anti-ontological counterparts is unfounded.  Had one started from the assumptions of the anti-ontological arguments, they would have found equal disproof for the premises of the ontological argument.  But which argument holds logical priority?  Neither!

This argument is different.  While it still grounds the logical possibility of the first premise on the benefit of the doubt, it is not disrupted by symmetrically granting the possibility of its contradictory.  Fair is fair!  To push the argument further two varieties of parody arguments are considered, possibility is granted, and they are shown to be consistent with the conclusions of the meta modal ontological argument. So while older versions of the ontological arguments are blocked by symmetry, this argument is not.  Again, we might be tempted to restrict the benefit of the doubt, or presumption of possibility, in light of this proof, but such a restriction seems a bit ad hoc and potentially destructive to modal reasoning generally.  We’d have to propose a principle that prevents this argument, but still permits other varieties of modal proofs that rely upon benefit of the doubt based modal reasoning.  But struggling to manufacture just the right restrictions is merely to assume a conclusion and to work backwards to prevent an argument that conflicts with that conclusion!  This would be reminiscent of the old logical positivist project of developing a working verification principle that restricts meaning to only those propositions that positivists thought should be meaningful.  Any restrictive principle they developed was either too restrictive, not restrictive enough, or self-defeating.  All of this is to say that it is legitimate to assume the logical possibility of something that is epistemically possible, so long as one is also willing to grant the logical possibility of the contradictory.  That is, one should presume possibility of something not known to exist actually or necessarily only if the possibility is granted to both the existence and non-existence of the possibility in question and there are no known reasons to think it impossible.

The argument is as follows…

Let

Ax =df x is a sound modal ontological argument concluding to the existence of a sufficiently defined divine being.
Cx =df x is the conclusion of a sound modal ontological argument that asserts the existence of a sufficiently defined divine being.
Θxy =df x is sufficiently defined as a divine being by proposition y.

T1. ◊(∃x)Fx → (∃x)◊Fx (Barcan Formula)
T2. ◊□(∃x)Fx → □(∃x)Fx (S5 axiom)

1.  ◊(∃x)Ax (premise)
2.  ◊(∃x)Ax → ◊(∃y)Cy (premise)
3.  (∀y)(◊Cy → ◊□(∃z)Θzy) (premise)
4.  ◊(∃y)Cy (1,2 MP)
5.  ◊(∃y)Cy → (∃y)◊Cy (T1)
6.  (∃y)◊Cy (4,5 MP)
7.  ◊Cu (6 EI)
8.  ◊Cu → ◊□(∃z)Θzu (3 UI)
9.  ◊□(∃z)Θzu (7,8 MP)
10.  ◊□(∃z)Θzu → □(∃x)Θzu (T2)
11.  □(∃x)Θzu (9,10 MP)
12.  (∃z)Θzu (11, NE)

To prove no disruption on first level symmetry, we grant

13.  ◊¬(∃x)Ax (premise)

And (13) is shown to be consistent insofar as one might defend this premise,

14.  ◊¬(∃x)Ax → (∀y)(◊¬(∃z)Θzy ∨ ◊(∃z)Θzy) (premise)

To prove there is no disruption what might be called a second level symmetry, consider the following additions:

Bx =df x is a sound modal anti-ontological argument concluding to the non-existence of a sufficiently defined divine being.
Dx =df x is the conclusion of a sound modal anti-ontological argument that asserts the non-existence of a sufficiently defined divine being.

15.  ◊(∃x)Bx (premise)
16.  ◊(∃x)Bx → ◊(∃y)Dy (premise)
17.  (∀y)(◊Dy → ◊□¬(∃z)Θzy) (premise)
18.  ◊(∃y)Dy (15,16 MP)
19.  ◊(∃y)Dy → (∃y)◊Dy (T1)
20.  (∃y)◊Dy (18,19 MP)
21.  ◊Dv (20 EI)
22.  ◊Dv → ◊□¬(∃z)Θzv (17 UI)
23.  ◊□¬(∃z)Θzv (21,22 MP)
24.  ◊□¬(∃z)Θzv → □¬(∃x)Θzv (T2)
25.  □¬(∃x)Θzv(23,24 MP)
26.  ¬(∃z)Θzv (25, NE)
27.  ¬(∃z)Θzv · (∃z)Θzu (12,26 Conj)

It is not evident that (27) is a direct contradiction without the further premise,

28*.  v = u (premise)

But there is no reason to presume this identity, at least there is no more reason to assume (28*) than there is to presume,

28′. v ≠ u (premise)

Further, we should take the fact that a contradiction would be generated by claiming identity between v and u as prima facie evidence that they are not identical.  And so, this version of the meta modal ontological argument successfully demonstrates that there exists a being that is sufficiently defined as divine by some proposition.  In other words, a divine being exists, which is shown by these last two steps,

29.  (∃z)Θzu (27, Simp)
30.  (∃x)(∃z)Θzx (29, EG)

That is, by (30) we have proved that there exist some x and some z such that z is sufficiently defined as a divine being by proposition x.  Or, to put it simply, there exists some such being that can be sufficiently defined as a divine being.  As far as I can tell, that means that God exists.

In future posts, I hope to defend the key premises in a bit more detail, along with my use of the S5 axiom and Barcan Formula.  In the meantime, I would appreciate any challenges, criticisms, questions, or suggestions.

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