Although the basic ideas of the ontological argument can be found in Aristotle and Philo Judaeus, the argument received its classical formulation in Anselm's Proslogion and his Reply to the objections raised by Gaunilo. During the succeeding nine centuries the argument has had a chequered career. It was supported by some scholastic theologians but rejected by Aquinas. Descartes and Leibniz offered their own versions of the proof but Kant's refutation of the argument has generally been accepted as conclusive during the past century and a half. Nevertheless, interest in the proof has never completely disappeared—perhaps provoked by Aquinas' suggestion that the proof may be valid for God even though it cannot be valid for us because of the inadequacy of our knowledge of God. Recently there has been a revival of interest in the ontological argument. J. N. Findlay put the argument into reverse to show the necessary non-existence of God in an article in 1948 but in later writings he has suggested that the argument may have positive significance. In 1960 Norman Malcolm published a paper in which he distinguished two basically different forms of the ontological argument in the Proslogion and defended the possible validity of the second of them.