The Modal Ontological Argument

Abstract

We know more today about the second, or so-called 'modal', version of St. Anselm's ontological argument than we did when Charles Hartshorne and Norman Malcolm brought it to the attention of philosophers some years ago. 1 But there is still much to be learned. Criticisms of the modal ontological argument focus on its premises, namely (i) the claim that perfection, or maximal greatness, implies necessary existence, and (ii) the claim that the existence of a perfect being is logically possible. Less attention has been given by the critics of the argument to the modal principles that allow one to get from these premises to the conclusion that a perfect being exists. The modal ontological argument is valid in some standard systems of alethic modal logic, e.g., S5 (which is assumed by advocates of the argument like Hartshorne and Plantinga), and in at least one weaker system. But it is not valid in all. For example, it is not valid in T (Von Wright's M) or any Lewis system weaker than S5, including S4. What should all this mean for our assessment of the argument? Is choosing a modal system in theological contexts as innocent as choosing hors d'oeuvres? Can it be so with a proof for the existence of God at stake? Reflecting on these questions leads to two important, though often neglected, objections to the modal ontological argument (hereafter the 'modal OA'). The narrower aim of this paper is to explore these two objections; the wider aim, continuous with the narrower one, is to describe the present status quaestionis concerning the argument. As I see it, there are three central, as yet unresolved, problems that stand in the way of accepting the modal OA. Two of these problems are associated with the two objections just mentioned. The third problem will be mentioned here, but not discussed at length, because it is better understood than the two problems I shall discuss and has been widely discussed in the literature. I am not myself sure how to respond to all of these