The Ontological Argument is one of the five traditional arguments for the
existence of God. It is a priori; i.e it is not dependent on experience but
instead attempts to use logical reasoning. The classical versions of the
Ontological argument are raised by St Anselm and Descartes, with Alvin
Platinga providing a more modern theory. Ontological means "concerned
with being"; the argument was named by neither of the these previously
mentioned philosophers but by Immanuel Kant.
Anselm outlined two versions of the argument and these are found in his book,
Proslogian (1078) through the form of a prayer, directed at the Fool of Psalm 14 who
says, in his heart, "there is no God". His argument is based on a "reductio ad
absurdum" which attempts to prove something by reducing the very opposite to being
absurd.
Anselm's second version of the argument is what he believes to be important in refuting Gaunilo's main criticism of a
"perfect island". Anselm's starting point is that God is an absolutely perfect being and one who cannot be surpassed in
greatness. The greatest conceivable beings existence cannot be contingent as this would be mean there could be a
greater being, with necessary existence. Thus, the greatest conceivable being has necessary existence; i.e. the idea of
something you cannot imagine not existing. He concluded that if God has necessary existence then he clearly exists.
Anselm used the analogy of a painter to show that God can be understood as a concept and understood to
exist. He claims a painter has an idea of what his masterpiece will look like before it's painted; the painter
understands the concept of the painting even though he doesn't understand it to exist. After painting his
masterpiece the painter will understand both the concept of the painting and of it existing. Anselm is trying to
say that even the "fool" can grasp the concept of God.
Anselm begins his first argument by saying that from the idea of
God, we understand a being who is "that than which nothing
greater can be conceived". He then argues that the greatest
conceivable being would not be such if he only existed in our
minds. For a greater being would be one that not only existed in
our minds but in reality also.
Thus, as we are imagining the greatest conceivable being, we must
be thinking of a being who exists in both our minds and in reality.
God must therefore exist in both the mind and
reality.