Plantinga's Modal Ontological Argument for God

Instructor: Joshua Sipper

Dr. Sipper holds a PhD in Education, a Master's of Education, and a Bachelor's in English. Most of his experience is in adult and post secondary education.

Dr. Alvin Plantinga is regarded as one of the foremost religious philosophers of the contemporary era. His modal ontological argument for foundational religious necessity is seen as an almost airtight defense of religion.

Dr. Alvin Plantinga

Have you ever tried to prove something by purely reasoning it out based on what makes the most logical sense? This is the basic idea of modal ontological analysis. Dr. Alvin Plantinga, professor of philosophy at Notre Dame, is an expert in this particular type of philosophical analysis and argumentation. In fact, his modal ontological argument is considered one of the most articulate and comprehensive arguments for the existence of God to date.

Basically, Plantinga's argument looks at the how God in possible worlds is necessary and uses this point to show how he is necessary for all possible worlds. A more in-depth analysis of Plantinga's argument is forthcoming, but it is often all about what is possible and necessary.

What is an Ontological Argument Anyway?

The ontological argument for God's existence was first laid out in the form we see today by Anselm of Canterbury (1033--1109) who was a monk living in France and England and writing about philosophy and theology. Anselm wrote the ontological argument from the perspective of someone without the need for prior information about or experience of God, or a priori.

So how does this work? Anselm lays out his argument like this:

God is the greatest being one can conceive --> Is there a being that meets the definition we assign to God? --> If so, then I have an understanding of God in my own mind that is not based on prior understanding --> I then have an understanding of God's existence --> Hence, God exists in the understanding of a person --> But, God cannot exist in the understanding alone because He is the greatest being that can be conceived, thus God must exist in reality which is greater than understanding alone --> Therefore, God exists.

St Anselm was the originator of the Ontological Argument.
Anselm of Canterbury

What Does Modal Mean?

To put it simply, modal logic is a type of logical argumentation that uses words like 'possible' and 'necessary' to guide thoughts toward a conclusion. For instance, you could say that it is 'possible' to learn by merely listening to a teacher talk about a topic, but it is 'necessary' to study in order to pass the test. This is a very simple expression of the modal argument, but it gets the point across.

Basically, in modal logic, you are trying to show that if some things are possible, then they must exist or make some kind of difference in the real world.

A philosopher using modal logic will also say that some things are 'necessary'. For example, a common phrase in modal logic is that God is a 'necessary being' or that if God did not exists, then nothing else could either.

Modal logic often uses the terms possible and necessary.
Modal Logic

Putting the Pieces Together: Plantinga's Modal Ontological Argument

Dr. Plantinga's modal ontological argument includes many of the aspects of Anselm's original argument but includes various additions and changes. Plantinga basically uses a possible world analysis. In other words, he says that in any possible world, something might be actual and that there are many possible worlds, so the possible must be actual in one of those many possibilities. He then takes that actuality to the next level by saying that in that possible world, the actual thing, since it is actual, must be necessary and therefore must exist in all possible worlds.

Here's how it breaks down:

1. If God exists, He must exist necessarily

2. Either God exists necessarily or He doesn't

3. If God doesn't have necessary existence, then He necessarily doesn't


4. Either God has necessary existence, or he necessarily doesn't

5. If God necessarily doesn't have necessary existence, then God necessarily doesn't exist


6. Either God has necessary existence, or he necessarily doesn't exist

7. It is not the case that God necessarily doesn't exist


8. God has necessary existence

9. If God has necessary existence, then God exists


10. God exists

As you can see, Plantinga uses the word necessarily over and over again to move his argument along. While this might seem redundant, it's (no pun intended) necessary. As you examine the argument, around numbers 6 and 7 it can begin to get sort of fuzzy. So, let's break it down just a little bit more.

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