ABSTRACT
Rene Descartes’s argument and Anselm’s argument are generally classified as different “versions” of the same argument: each is customarily described as a version of “the ontological argument.” It is not necessary to make use of the concept of a possible world in presenting the “modal ontological argument,” but it is advisable, since the English grammatical constructions used in formulating modal reasoning are sources of much ambiguity, and this ambiguity can cause logically invalid arguments to look as if they were valid. The ontological argument is, or claims to be, a proof of the existence of a perfect being. The validity of the modal ontological argument depends on the assumption that what is intrinsically possible has that status as a matter of necessity. In order to state the modal ontological argument, we need two notions: the notion of a necessary being and the notion of something’s having a property essentially.
