Plantiga's ontological argument.
November 8, 2011 at 6:28 pm
(This post was last modified: November 8, 2011 at 6:30 pm by Mystic.)
This is from Wikipedia:
Alvin Plantinga has presented another version of the argument. The conclusion he provides logically follows from the premises, assuming axiom S5 of modal logic - if possibly p, then necessarily possible p and if possibly necessarily p, then necessarily p. A version of his argument is as follows[43]:
A being has maximal excellence in a given possible world W if and only if it is omnipotent, omniscient and wholly good in W; and
A being has maximal greatness if it has maximal excellence in every possible world.
It is possible that there is a being that has maximal greatness. (Premise)
Therefore, possibly it is necessarily true that an omniscient, omnipotent and perfectly good being exists.
Therefore (by axiom S5) it is necessarily true that an omniscient, omnipotent and perfectly good being exists.
Therefore, an omniscient, omnipotent and perfectly good being exists.
This argument has two controversial premises: The axiom S5 and the "possibility premise" that a maximally great being is possible.
S5 is widely but far from universally accepted. For instance, Paul Almond strongly disagrees with the argument based on the "incoherence, incorrectness and triviality" of axiom S5.[44]
The more controversial premise is the "possibility premise". One objection by Richard M. Gale, professor emeritus of philosophy at University of Pittsburgh, is that the "possibility premise" begs the question, because one only has the epistemic right to accept it if one understands the nested modal operators, and if one understands them within the system S5 (without which the argument fails) then one understands that "possibly necessarily" is basically the same as "necessarily"
Now axiom S5 can be derived from the proposition "Possibly P, implies necessarily possibly P".
The argument that it's circular doesn't seem that convincing because it's arguing that if it's possible, then it's necessarily based on this axiom, but it's not simply stating it's necessarily.
Now the controversial axiom seems to be if God is possible in a possible world P. But I don't see how this is a disputed premise, how can it be that God is not possible in any possible world?
However the premise " A being has maximal greatness if it has maximal excellence in every possible world." Does not mean a Being has maximal greatness only if has maximal greatness in every possible world. Rather it seems if there is no possible world with a being with more possible greatness, then it's the maximal greatness.
The conclusion doesn't seem to follow then. However it can be argued a necessary being is possible in a world p. What is meant by necessary is not simply necessary for that world, but necessary in all worlds. But to argue that as possibly true, you have to know that God is necessary in this world and necessary for all possible worlds. So it seems rather circular to do so.
Alvin Plantinga has presented another version of the argument. The conclusion he provides logically follows from the premises, assuming axiom S5 of modal logic - if possibly p, then necessarily possible p and if possibly necessarily p, then necessarily p. A version of his argument is as follows[43]:
A being has maximal excellence in a given possible world W if and only if it is omnipotent, omniscient and wholly good in W; and
A being has maximal greatness if it has maximal excellence in every possible world.
It is possible that there is a being that has maximal greatness. (Premise)
Therefore, possibly it is necessarily true that an omniscient, omnipotent and perfectly good being exists.
Therefore (by axiom S5) it is necessarily true that an omniscient, omnipotent and perfectly good being exists.
Therefore, an omniscient, omnipotent and perfectly good being exists.
This argument has two controversial premises: The axiom S5 and the "possibility premise" that a maximally great being is possible.
S5 is widely but far from universally accepted. For instance, Paul Almond strongly disagrees with the argument based on the "incoherence, incorrectness and triviality" of axiom S5.[44]
The more controversial premise is the "possibility premise". One objection by Richard M. Gale, professor emeritus of philosophy at University of Pittsburgh, is that the "possibility premise" begs the question, because one only has the epistemic right to accept it if one understands the nested modal operators, and if one understands them within the system S5 (without which the argument fails) then one understands that "possibly necessarily" is basically the same as "necessarily"
Now axiom S5 can be derived from the proposition "Possibly P, implies necessarily possibly P".
The argument that it's circular doesn't seem that convincing because it's arguing that if it's possible, then it's necessarily based on this axiom, but it's not simply stating it's necessarily.
Now the controversial axiom seems to be if God is possible in a possible world P. But I don't see how this is a disputed premise, how can it be that God is not possible in any possible world?
However the premise " A being has maximal greatness if it has maximal excellence in every possible world." Does not mean a Being has maximal greatness only if has maximal greatness in every possible world. Rather it seems if there is no possible world with a being with more possible greatness, then it's the maximal greatness.
The conclusion doesn't seem to follow then. However it can be argued a necessary being is possible in a world p. What is meant by necessary is not simply necessary for that world, but necessary in all worlds. But to argue that as possibly true, you have to know that God is necessary in this world and necessary for all possible worlds. So it seems rather circular to do so.
