By David P. Diaz, Ed.D.
Anselm of Canterbury, an Italian Benedictine monk, philosopher, and theologian, is credited with originating the ontological argument. The ontological argument considers the possibility that a maximally great being exists. The argument is primarily philosophical. That is, it doesn’t appeal to empirical (i.e., scientific) evidence but depends on internal reflection and reasoning.
Like other theistic arguments, there are many versions of the ontological argument. In modern times, the one offered by philosopher Alvin Plantinga has emerged as a frontrunner. It attempts to show that if it is possible that a maximally great being exists, then a maximally great being exists necessarily.
Is it possible to develop a general concept of a maximally great being? What would it be like? What attributes would it possess? A “maximally great being” can be defined as one that would have at least the following qualities (and perhaps others): (1) It would know everything that there is to know (i.e., it would be omniscient); (2) it would be maximally powerful (i.e., it would be omnipotent); and (3) it would be morally perfect (i.e., it would possess unlimited goodness). Ask yourself, “Is such a being conceivable, at least in some possible world?”
Plantinga’s argument goes something like this:
Premise 1: It is possible that a maximally great being exists.
Premise 2: If 1, then a maximally great being exists in some possible world.
Premise 3: If such a being exists in some possible world, it exists in every possible world.
Premise 4: If such a being exists in every possible world, then it exists in the actual world.
Premise 5: And if it exists in the actual world, then a maximally great being exists.
Conclusion: A maximally great being exists.
One can challenge premise 1 and say that it is impossible that a maximally great being exists. However, unless one possesses all knowledge, how could one claim that anything is impossible? No one knows the limits of what we can and cannot know. Indeed, no one knows what there is to be known. Therefore, it seems possible that a maximally great being does exist.
On the other hand, one might legitimately question Premise 3: If a maximally great being exists in some possible world, why must it also exist in every possible world? In response, one might say: For any being that is maximally great, it is greater for such a being to exist in all possible worlds than in just one possible world. Therefore, if a maximally great being exists in any possible world, it must exist in every possible world. In other words, a being wouldn’t be maximally great if it only existed in some possible worlds, so it must exist in every possible world.
Not everyone who reflects on the concept of a maximally great being will accept it. Moreover, the argument is not intended to “prove” the existence of God but, rather, is only intended to establish the rational acceptability of believing in such a being. In other words, those who accept this argument can be rationally justified in doing so. Plantinga concedes that a rational person need not accept this argument and claims only that a rational person could accept it. In other words, one could be rational and deny this argument but one is also rationally justified in believing it.
About the Author
David P. Diaz, Ed.D., is an author, retired college professor, and publisher of Things I Believe Project. His writings have spanned the gamut from peer-reviewed technical articles to his memoir, which won the 2006 American Book Award. Dr. Diaz holds a Bachelor’s and Master of Science degree from California Polytechnic State University, a Master of Arts in Philosophical Apologetics from Houston Christian University, and a Doctor of Education specializing in Computing and Information Technology from Nova Southeastern University.
 A possible world does not refer to a parallel dimension or some specific place in a multiverse; it simply refers to a possible description of reality. To say that a being exists in a possible world is just to say that if the world were that way, then such a being would have existed.
 From William Lane Craig, Defenders Class: The Ontological Argument for God – Part 1 (Defenders Class: March 14, 2011).