The ontological argument is still a very popular argument to prove the existence of God by use of reason alone, despite strong attacks over the years from; Aquinas, hume, kant and most recently Russell. Modern version of the argument from Plantinga and Malcolm claim that there is a universe but it contingent therefore whatever the explanation for the universe cannot be contingent itself but is necessary. The ontological argument is a priori therefore is also deductive and analytic argument meaning comes the to the conclusion of the existence of god based on the definition of God used in the premises.
The ontological argument was developed in 1073. Anselm wrote the matter of christian faith of tradition was ‘faith seeking understanding’ he described God as ‘That than which nothing greater can be conceived’ Anselm prayed for a single short argument for the prove of the God including the nature and existence. As a result’ suddenly one night at matins the grace of God illuminate his heart the whole matter became clear in mind’ the proslogian. The ontological argument was born.
For Anselm, the existence of god was not only true by virtue faith but also logical necessity. Anselm was trying to prove the existence of God by meaning of Reductio ad Absurdum. In Anselm case the opposite would be that God does not exist, which he aimed to prove was absurd by meaning of an argument demonstrating that the existence of God is logically necessary. Anselm argument was rejected by other christian thelolgical on the ground that human intellect is too weak to know enough of God essence and nature to be able to deuce from his necessary existence.