It was Anselm that first formulated an argument for existence of God,and then I.Kant made a famous objection that existence is not a proper predicate.In terms of modal logic,C.Hartshorne,A.Plantinga and K.Gdel constructed their own modal versions.This paper is an attempt to contrast those versions.Hartshorne didn’t distinguish logical possibility from metaphysical possibility;Plantinga employed his modest modal theory and developed a version which can avoid Kant’s criticism,and this further shows that the real concern about ontological argument is premises;Gdel’s version suggests that "necessary existence" is one of positive properties,and therefore can also be challenged by Kant.Above all,there is no ontological argument without premises,so the necessary step for further study is to give a good account for its premises.