## The Validity of Plantinga’s Ontological Argument

In 1974 Alvin Plantinga developed a modal version of the ontological argument, which is as follows:

1. The property of being maximally great is exemplified in some possible world.
2. The property of being maximally great is equivalent, by definition, to the property of being maximally excellent in every possible world.
3. The property of being maximally excellent entails the properties of omniscience, omnipotence, and moral perfection.
4. A universal property is one that is exemplified in every possible world or none.
5. Any property that is equivalent to some property that holds in every possible world is a universal property.
6. Therefore, there exists a being that is essentially omniscient, omnipotent, and morally perfect (God).

Let,

Ax =df x is maximally great

Bx =df x is maximally excellent

W(Y) =df Y is a universal property

Ox =df x is omniscient, omnipotent, and morally perfect

1 ◊(∃x)Ax                                                     pr

2

### 10 Comments to “The Validity of Plantinga’s Ontological Argument”

1. Hey there, Max! I love your posts – I read all of them as they come out. I’m an undergraduate philosophy major – so reading your work is very inspiring.

About the ontological argument: I know it uses modal logic, right? And modal logic a type of symbolic logic?

Can you recommend a book or online introduction to this type of logic? Either modal or symbolic? I’m really interested in trying to learn this material outside of school.
I’m taking a formal logic class next semester, but I would love to get a head start.

2. Michael,
You might look into Kenneth Konyndyk’s book:
http://www.amazon.com/Introductory-Modal-Logic-Kenneth-Konyndyk/dp/0268011591
He introduces the various systems of modal logic.

3. I appreciate both of those responses! I’ll definitely be looking into those. Thanks!

4. I would say Plantinga’s books themselves, like The Nature of Necessity, are excellent resources on modal logic. He did a lot of groundwork. As an undergrad, you should also hopefully have access to journals for free through your library. If you go to a resource, say the Stanford Encyclopedia of Philosophy, and look at their references, you should get some good articles. One article I found interesting was by Michael Tooley called Plantinga’s Defence of the Ontological Argument (Mind, 1981). In it, Tooley gives some reasons why this argument may not work due to reliance on certain questionable factors in modal logic. I’d get your feet wet in modal logic before reading it, though.

Hope that helps.

5. What about that objection that his premise is the same as his conclusion?

• Where do you see that? 6 is the conclusion and I don’t see how that is equivalent to any of the preceding premises because that would certainly be an issue.