Brian Bosse
"The Brain"
I realize there are many Christians who think the traditional arguments for the existence of God are not sound. I would like to explore this claim with the ontological argument. I will present a modified argument based on the formal modal argument presented in Hartshorne’s The Logic of Perfection, Open Court, 1962, p. 51.
A Formal Presentation of the Ontological Argument
p = there exists a God such that He is a perfect being.
Modal Operators
□p = p is necessarily true. That is to say, that in all possible worlds p is true.
◊p = p is possibly true. That is to say, there exists a possible world where p is true.
p = p is actually true. That is to say, in the actual world, p is true.
It should be noted that we can define both □ and ◊ in terms of each other. For instance:
Rule N: □p ↔ ¬◊¬p.
Rule P: ◊p ↔ ¬□¬p.
Logical Rules
A. Disjunctive Syllogism: [(a V b) Λ ¬b] → a
B. Modus Ponens: [(a → b) Λ a] → b
C. Modal Modus Tollens: [□(a → b) Λ □¬b] → □¬a
D. Substitution: [(a V b) Λ (b → c)] → (a V c)
E. Becker’s Postulate: □a → □□a; ◊a → □◊a (Modal status is always necessary.)
F. Excluded Middle: a V ¬a
G. Modal Axiom: □a → a
Formal Proof
1. □(p → □p) (Anselm: It is necessarily the case that if there exists a perfect God, then this God necessarily exists.)
2. ¬□¬p (Anselm: It is not necessarily the case that there does not exist a perfect God. This is the same as saying: It is possible for there to exist a perfect God, i.e. ◊p by Rule P.)
3. □p → p (Rule G)
4. □p V ¬□p (Rule F)
5. ¬□p → □¬□p (Rule E)
6. □p V □¬□p (Rule D – 4 and 5)
7. □¬□p → □¬p (Rule C – 1)
8. □p V □¬p (Rule D – 6 and 7)
9. □p (Rule A – 8 and 2)
10. p (Rule B – 3 and 9)
If this proof is not sound, where and why does it break down?
Sincerely,
Brian
A Formal Presentation of the Ontological Argument
p = there exists a God such that He is a perfect being.
Modal Operators
□p = p is necessarily true. That is to say, that in all possible worlds p is true.
◊p = p is possibly true. That is to say, there exists a possible world where p is true.
p = p is actually true. That is to say, in the actual world, p is true.
It should be noted that we can define both □ and ◊ in terms of each other. For instance:
Rule N: □p ↔ ¬◊¬p.
Rule P: ◊p ↔ ¬□¬p.
Logical Rules
A. Disjunctive Syllogism: [(a V b) Λ ¬b] → a
B. Modus Ponens: [(a → b) Λ a] → b
C. Modal Modus Tollens: [□(a → b) Λ □¬b] → □¬a
D. Substitution: [(a V b) Λ (b → c)] → (a V c)
E. Becker’s Postulate: □a → □□a; ◊a → □◊a (Modal status is always necessary.)
F. Excluded Middle: a V ¬a
G. Modal Axiom: □a → a
Formal Proof
1. □(p → □p) (Anselm: It is necessarily the case that if there exists a perfect God, then this God necessarily exists.)
2. ¬□¬p (Anselm: It is not necessarily the case that there does not exist a perfect God. This is the same as saying: It is possible for there to exist a perfect God, i.e. ◊p by Rule P.)
3. □p → p (Rule G)
4. □p V ¬□p (Rule F)
5. ¬□p → □¬□p (Rule E)
6. □p V □¬□p (Rule D – 4 and 5)
7. □¬□p → □¬p (Rule C – 1)
8. □p V □¬p (Rule D – 6 and 7)
9. □p (Rule A – 8 and 2)
10. p (Rule B – 3 and 9)
If this proof is not sound, where and why does it break down?
Sincerely,
Brian