Objections based on the possibility of deriving
existential claims from definition and the reponses
1.1 The ontological argument, which uses a priori logic, states
that God being defined as most great or perfect must exist,
since a God who exists is greater than a God who does not.
St. Anselm of Canterbury proposed the first version in
which he defined God as 'the greatest conceivable being'.
Definitions can only tell us what God would be like if he
existed, they cannot establish whether or not he did. There
have been many objections made to the OA based upon the
possibility of deriving existential claims from definition such
as Anselm and Descartes.
2.1 Gaunilo of Marmoutiers claimed that Anselm's argument
allowed you to define anything into existence. He
responded to Anselm's claim that even 'the fool' can accept
the existence of God. He wrote 'On behalf of the fool' where
he said that just because the atheist has an understanding
of God as the GCB does not follow that we can conclude
God exists in reality. An idea in the mind does not mean it
has to exist.
2.2 Gaunilo also sets up a parallel argument for the critique of the
OA where he removes the word 'being' from Anselm's concept
of the GCB and substitutes it for island. He created his own
version of the OA to prove this island existed, comparing it to
other, less perfect islands. He argued that it would be absurd
to conclude such an island existed in reality. For Gaunilo
therefore, the fact you can define the greatest conceivable
being does not mean that such a being exists. Therefore the
structure of Anselm's argument would allow to prove the
existence of anything that could exist in our minds.
3.1 Thomas Aquinas claimed that we cannot prove 'God
exists' by definition. He also claimed that we cannot prove
God exists from an idea of God. In fact, God is beyond our
understanding, so we cannot define him. Therefore a priori
arguments to prove the existence of God fail. Aquinas
claimed that the only way we can know God is through
things we can experience, e.g. evidence of design in nature.
The existence of God must be known from experience (a
posteriori) not by a priori argument.
4.1 David Hume's 'Dialogues Concerning Natural Religion'
contains an argument presented by Cleanthes against
the possibility of proof of an a priori of God's existence.
He argued that it is impossible to start off with a
definition of God and to use logic to conclude 'God
exists.' Hume was a sceptical empiricist who believed
that experience, especially of the senses, is the only
source of knowledge. Many would agree with Hume that
humans base their lives on things we observe rather
than things we can prove through logic. Therefore, the
ontological argument can be rejected.
5 RESPONSE: NORMAN MALCOLM
5.1 For Malcolm, it is not possible to think of a being
that necessarily exists to not exist. In the case of
the statement 'God necessarily exists' there are 3
possibilities - impossible, this can't be the case are
there are no contradictions. Probable - God is
necessary, Malcolm maintains this cannot be the
case and true - the only alternative left and so must be the case