The Ontological Argument
The ontological argument is based on the claim that God's existence can be deduced from his definition. Once
God is correctly defined, there can be no doubt that God exists. The argument claims:
● The proposition ‘God exists’ is a priori and deductive - you do not need sense experience to know that it
is true; you know it is true just by thinking about God and His nature.
● In the same proposition, the subject ‘God’ contains the predicate ‘exists’, so God must exist, e.g., bicycles
(subject) have two wheels (predicate) - ‘God exists’ follows the same logic.
● God’s existence is a necessary truth, not a contingent one.
Key Facts About the Argument (St. Anselm’s classical argument):
● ‘Ontos’ (Greek word) is concerned with ‘being’.
● Argument is a priori analytic: it analyses the concept of God in the same way as G Perfecti
other concepts, e.g., ‘bachelor’ contains the concepts of ‘man’ and ‘unmarried’ od on
- these concepts are entailed in the concept of ‘bachelor’. In the same way, our
concept of God contains the concept of perfection, which in turn contains the Existen
concept of existence, i.e., if God didn’t exist, He would not be perfect, which
would lead to a contradiction (reductio ad absurdum).
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● Comes from a ‘faith-seeking understanding’ rather than an attempt to convert
the atheist (hence why Anselm is writing this argument not as a logical argument, but rather in a prayer
form) - Anselm knows God exists because he has experience with God (works in the Church). This shows
belief in God is rational and logical, making stereotypes against religious believers unjustifiable.
● Anselm is responding to Psalms 14 and 53 where ‘The Fool says to himself ‘There is no God’’ (see P2).
The Formal Argument:
P1: God is ‘a being than which nothing greater can be conceived’.
P2: This is a definition which even a fool understands in his mind, even though he does not understand it
to exist in reality.
P3: There is a difference between having an idea in the mind and knowing that this idea exists in reality.
P4: For example, a painter has an idea in his mind of what he wants to paint, but when he has painted,
that idea now exists both in his mind and in reality.
P5: It is greater to exist both in the mind and in reality than to exist only in the mind.
P6: If God existed only in the mind, I could think of something greater: a God who existed in reality also.
C: Therefore, in order to be the greatest conceivable being (P1), God must exist both in the mind and in
reality.
P1 - Anselm means ‘greatest’ in every way possible: omnipotent, omniscient, and must possess every great-
making quality to the highest possible level. Anselm expects everyone will accept this (working) definition of God.
This is a strength of the argument as Anselm begins (P1) with a definition of God that theists and atheists can
accept as it is not dependent on religious beliefs.
P1 and C: God’s existence is analytic - once we analyse the definition of the term, we will see that God exists.
P5 - Anselm claims it is greater to exist both in the mind (in intellectu) and in reality (in re) than to only exist in
the mind - seems like a reasonable claim, e.g., we can think about the necessities of life like food and water, but
being able to eat a drink in reality is much greater than simply thinking about it. P5 is also a reductio ad
absurdum: to deny the statement would be an absurdity. If God does exist in the mind alone, He is not the
greatest possible being.
This can be summarised into:
P1: God is the greatest conceivable being.
P2: It is greater to exist in reality than to exist only in the mind.
C: Therefore, as the greatest conceivable being, God must exist in reality.
, Simple Explanation: Something is greater if it exists than if it doesn’t. If God is the greatest thing imaginable, He
must exist. For if He didn’t, you could imagine something greater - something with all His qualities (predicates),
but which did actually exist (existence is therefore a predicate).
Gaunilo’s Criticism:
Gaunilo opposed Anselm’s argument: he argues we cannot prove God by definition because we cannot
comprehend his true nature. Aquinas supports this: ‘We as sinful humanity cannot understand the mind of God’.
However, it can be argued that though we may be limited in our description of God, we are not limited in our
conception of God (see Religious Language). Buddhism also may argue that we can conceive past our human
biology/psychology/nature.
Gaunilo’s argument uses a parody of Anselm’s argument to show it is absurd: Gaunilo gave an OA for the
existence of a ‘perfect lost island’ - an island than which nothing greater can be conceived - in which he used the
structure of Anselm’s argument:
P1: It is possible to conceive of the most perfect and real lost island.
P2: It is greater to exist in reality than to exist only in the mind.
C: Therefore, the most perfect and real lost island must exist in reality.
Gaunilo is using a reductio ad absurdum argument (latin for ‘argument to absurdity’) - he suggests Anselm’s
argument can be used to predict an endless number of perfect objects, so the real ‘fool’ would be anyone who
argued this way. We can show that a perfect island does not exist, so Anselm’s argument does not work.
Schopenhauer agrees with Gaunilo by saying Anselm’s argument is a ‘conjuring trick’ - intuitively, it does not
seem possible to prove the existence of something without a posteriori premises. We can test its validity by using
the same form but different content which will lead us to a false conclusion - we find it can be used to prove the
existence of almost anything, e.g.:
P1: X is the greatest possible Y.
P2: It is greater to exist in reality and in the understanding.
C: Therefore, X (if it is genuinely the greatest Y) must exist in reality.
However, Gaunilo’s criticism gave Anselm a chance to emphasise the second stage of his argument, so Anselm
arranged that the Proslogium should appear with Gaunilo’s criticism attached.
Anselm’s Response to Gaunilo (His Second Argument):
Anselm argues that you cannot possibly compare God with an island - we know islands have a beginning and likely
an end because they are contingent. An island does not have an external existence unlike God, who is unique,
eternal, and necessary. Anselm will argue that we cannot just think things into existence like Gaunilo claims
because it is not in their nature (definition) to necessarily exist because they are contingent beings.
Another issue is that if we imagined a different island each, everyone’s perspective and wants would be different -
God’s nature transcends human concepts and the contingency of those concepts. The concept of necessary
beings is not contingent on our human perspective, and so everyone must have one definition of God.
P1: To be perfect, an island would have to be ‘that island than which no greater can be conceived’.
P2: An island than which no greater can be conceived would have to exist necessarily, since a contingent
island would be less perfect than an island that existed necessarily.
P3: But islands are contingent, and so cannot exist necessarily.
C: Therefore, the logic of the argument related to a perfect island does not apply to God.
Further:
P1: God is the greatest conceivable being.
P2: The greatest conceivable being cannot be conceived not to exist.
C1: Therefore, God, and God alone, possesses necessary existence: God cannot not exist.
