The subsequent history of the ontological argument has been curious. It has been rejected by many considerable thinkers as a patent fallacy and by others regarded as the foundation of con structive thought. Descartes, who is sometimes held to be the father of modern philosophy, adopted it in two forms as the corner stone of his system, the bridge by which he passed from universal doubt to confidence in the possibility of knowledge. Descartes places in the forefront the consideration of the posses sion by the mind of the idea of an infinite and perfect being, and the question how this idea can originate. I cannot derive it from myself, because I am certainly neither infinite nor perfect. The idea then implies a really existent infinite and perfect Being as its source. Descartes adds an important element to.the argument by distinguishing between the positively infinite and the merely "indefinite." The latter is a negative idea implying simply the absence of limits, the former is concrete, and is the idea of God.
Unless I were in possession of the positive idea of infinity and perfection I should not know myself to be finite and imperfect. Descartes also states the ontological argument very much in the form given to it by Anselm. Though in all other instances it is possible to distinguish between essence and existence and to con ceive of a being as not existing, this is not possible in the single case of the idea of God. "The existence can no more be separated from the essence of God than the idea of a mountain from that of a valley. . . . It is not less impossible to conceive a God, that is, a being supremely perfect to whom existence is wanting, or who is devoid of a certain perfection than to conceive a mountain without a valley." (Meditations III. and V.) The ontological argument was also adopted by Leibniz, who made the addition to it that we need first to demonstrate that the idea of God is the idea of a possible existence.
The great flaw in the argument in its traditional form was clearly shown by Kant, who pointed out that it implies existence to be an attribute of the same nature as other attributes the absence of which would constitute imperfection, whereas this is not the case, since every concept we form is of a being as existing in some sense. Kant's illustration however, of the "hundred thalers," which are the same in properties in the imagination as in the pocket though not the same in usefulness, seems to miss the point even more obviously than Gaunilo's perfect island. The permanent value in the ontological argument has been emphasised by Hegel. It is the necessary attempt to bridge the gulf between thought and things, between concept and reality. In this sense it is really at the root of all thought. However we may express it, we are compelled to hold that what the mind necessarily thinks qua mind is real, that there is no impassable chasm between the "ordo idearum" and the "ordo rerum." All philosophies which
distinguish between appearance and Reality on the ground that the irrational cannot be the real, rest upon something akin to the ontological argument. Probably it would be better to say, "upon an ontological assumption." The ontological argument is, in truth, an attempt to put into the form of a train of reasoning a postulate without which the mind is helpless. It may be questioned therefore whether the ontological argument or postulate leads us directly to the God of religious experience. It leads rather to the conception of an absolute or rationally coherent system of being.
Before leaving the famous "three proofs" a remark must be made on their value for modern Theism. Before Kant's drastic criticism they were taken to be demonstrative proofs of the existence of God at least by the rational theologians. It is clear that as demonstrations they are unsatisfactory. This does not mean, however, that they are devoid of value. The post-Kantian Theist would, in most cases, adopt a different approach to his problem. The central question of constructive philosophy does not present itself to him in the form : given the idea of God as a belief, to find some rational proof of His existence. Rather the problem presents itself as analogous to the scientific problem: given the universe as disclosed in experience, to find the most reasonable account of it. Several hypotheses present themselves for consideration, among them Theism. The question before the mind of the philosopher, therefore, is to decide which of the pos sible hypotheses squares most adequately with the whole experi ence of the universe which is open to us. The Theist maintains that his hypothesis is the most rational in this sense. The tradi tional arguments, on this view, call attention to various aspects of the universe which, when taken up into reflective thought, go to support the Theistic view. Thus in spite of their failure as demonstrative arguments they have great value as indicating lines of thought, suggested by experience, which tend to substantiate the Theistic theory. (For a fuller statement of this see W. R. Sorley, Moral Values and the Idea of God, and W. R. Matthews, Studies in Christian Philosophy.) The change in the method of approach to which we have referred in the preceding paragr7ph is reflected in the type of argument on which modern Theism has laid greatest stress. Though not putting on one side the "rational" proofs, the main appeal in the philosophy of Theism has been to considerations drawn more directly from experience, and particularly from moral and religious experience.