Alvin Plantinga’s Modal Ontological Argument

In this video, the Modal Ontological Argument developed by Alvin Plantinga in his work, The Nature of Necessity, is explained in easy to understand terms. This video is used courtesy of Inspiring Philosophy. Subscribe to his YouTube channel at:


Christian. Apologist. Undergrad. Missio Deo

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4 comments on “Alvin Plantinga’s Modal Ontological Argument
  1. William says:

    So I have a few objections to Plantinga’s modal ontological argument.

    1. First of all, Plantinga did not intend this argument to prove the existence of God. His only goal was to show that believing in God is reasonable, since a reasonable person can accept the premise that it is possible for God to exist, not that the argument should convince an atheist to believe in God.

    2. Atheistic philosophers have since denied even this status to the modal ontological argument, however, pointing out that the premise that it is possible that a necessary being exists is far too close to the conclusion that the necessary being actually exists to make the argument successful. It’s just another question begging argument.

    3. The first premise, which says that it is possible that God exists, is unsupported. We can only say whether or not something is logically possible without proof in simple cases that we have experience with, like the idea of grass, not in complex cases removed significantly from our experience, like the idea of God. For this kind of concept, we need proof, which is why proofs that such and such a concept is logically consistent are common in mathematics.

    4. The problem of evil infers the nonexistence of God from the existence of gratuitous evil – actually, since God is claimed to be a necessary being, the atheist only needs to say that gratuitous evil is logically possible. If gratuitous evil is logically possible, therefore, the ontological argument must be unsound. The resolution of this conflict will have largely to do with whether we have a stronger intuition that it is possible that God exists or that it is possible for there to be gratuitous evil, and the atheist may well have a stronger intuition of the latter.

    5. S5 modal logic, which Plantinga’s argument depends upon, is controversial, so it might be possible to prove God’s existence using S5 because S5 is invalid rather than because God actually exists.

    6. We can summon various Gaunilo’s island style objections to the modal ontological argument. The video objects to Gaunilo’s island in the form of the greatest conceivable unicorn, by saying that the unicorn is contingent rather than logically necessary. However, this backfires, because there is no more reason why an omnipotent, omniscient mind should be logically necessary than there is why a magical unicorn should be logically necessary.

    I conclude that the modal ontological argument fails, because it is circular, depends on multiple unsupported assumptions, ignores counterevidence, and can easily be parodied.

    • To be frankly honest, my area of expertise is not in modal logic, or philosophy of religion, as much as it is in theology and Christian apologetics. That being said, I do want to offer some answers to these objections as I understand them. Also, I should be clear that my belief in the existence of God does not rest solely on the modal ontological argument; nor does Christian theism stand or fall alongside the modal ontological argument (or any ontological argument for that matter). With that in mind I will proceed:

      1. I concede as much to you as to say that Plantinga does not intend for the ontological argument to be a de facto proof of the existence of God. Plantinga is fairly harsh in his critique of Anselm’s Ontological argument in his work “God And Other Minds,” going so far as to say that it, “smacks to much of magic.”

      2. You say, “Atheistic philosophers have since denied this status to the ontological argument,”… and that,”the premise that it is possible there is a necessary being is far too close to the conclusion.” You call this question begging. However, it seems to me that the outright atheistic rejection of even the slightest possibility of necessary existence is itself question begging. It is almost as if they are saying, “necessary existence would yield this result and hence we reject it for the sake of rejecting the result.” It doesn’t seem founded to me. There is a vast amount of philosophic work done in the fields of the possibility of necessary existence as demonstrated through the Principle of Sufficient Reason (see Leibniz) or some sufficiently weak causal principle (see Alexander R. Pruss). The arguments presented from these principles for necessary existence are valid, and do overcome many of the problems that have been raised in Leibnizian cosmological arguments. Calling it question begging seems out of hand, especially considering that Plantinga does not go out of his way to explain why it is that God’s existence is possible.

      3. You say, “The first premise, which says that it is possible that God exists, is unsupported.” Since you offer no definitive proof that God does not exist, then, by your standard, the claim that “It is possible that God does not exist,” is on par with the claim that God does exist. However, I would posit, along with the majority of Christian philosophers and theologians, that Natural Theology provides sufficient reason for us to be justified in believing that God exists.

      4. The problem of evil has been posited in many different ways, by many different thinkers throughout the ages. However, many Free Will defenses that have been presented provide a framework in which God and evil can co-exist. For sake of space in this comment, I will not take time to belabor the points of these free will arguments. Rather I will urge readers to reference Alvin Plantinga’s Free Will Defense, (presented in God And Other Minds), along with many other free will answers to the problem of evil.

      5. The controversial nature of S5 modal logic does not guarantee it’s invalidity. Frankly, that is the extant of my ability to answer this point, and my ignorance on this particular topic shows. I will put up a logical proof from Robert Maydole in the Blackwell Companion to Natural Theology that demonstrates the validity of Plantinga’s Arguments.

      6. The exposition of great making properties, among which would be necessity, provides reason to believe that God would be necessary. Again, the Principle of Sufficient Reason, or some Causal Principle, should be enough to give credence to the belief that God would, or at least could, be defined as a necessary being. At this point, it seems important to point out a disclaimer for the above video. The video is by no means a full exposition of Plantinga’s arguments. It is only intended to be a very brief, easy to understand summary. That being the case, it does not bring out all of Plantinga’s arguments.

      I hope that clarified some of my reasoning and my use of the video. Thanks so much for checking out my blog, William, and I hope you enjoyed it.

      • William says:

        Thanks for the civil and intelligent reply. The fact that you’re not an expert in philosophy of religion doesn’t disqualify you, in my view, because I think that almost anyone can evaluate an argument for or against the existence of God.

        2. Your response here was to call the atheistic claim that the modal ontological argument was question begging itself question begging. There’s not much to be said after that, because we’ve both called each other’s positions question begging and it is up to the reader to decide who has the more plausible position. I do want to add that Pruss’ reasoning in the Blackwell Companion to Natural Theology can be refuted in a paragraph, and I will be happy to do so if you’re interested.

        3. I agree that the claim that it is possible that God does not exist has the same status as the claim that it is possible God exists in the sense that we don’t know whether either proposition is true. However, I am not trying to make an argument based on the claim that it is possible that God does not exist.

        4. The free will defense cannot save theism against the relevant form of the problem of evil, because the free will defense does not show that it is logically impossible for gratuitous evil to exist. If God exists and is a necessary being, and if God’s existence is inconsistent with the existence of gratuitous evil, then there must be no gratuitous evil in any possible world. That’s a very strong claim to make, and an atheist might be perfectly reasonable in rejecting the modal ontological argument on the basis that his intuition that it is possible for there to be gratuitous evil is stronger than his intuition that it is possible that God exists.

        5. I don’t really have anything else to say about this.

        6. Your response here is that we can deduce the necessity of God from the idea of the greatest conceivable being. But it seems equally likely that we can deduce the existence of a magical unicorn from the idea of the greatest conceivable unicorn. I’m not sure what makes you think that the two are distinct.

  2. Your very welcome William! The fact that discussions like this often get so heated is really sad. I enjoy having intelligent and friendly discussions like this. And like I said, thanks for taking the time to check out my blog and engage these ideas. I would actually like to continue our discussions on this and other topics. We could even do that through email if you would like. And feel free to stop back by here any time you want.

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