Philosophy of Religion

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The Ontological Argument for the Existence of God

Anselm of Canterbury

The ontological argument for the existence of God, as it is found in its classical form, was first formulated by the eleventh century Benedictine monk, Archbishop and theologian, St Anselm of Canterbury (1033-1109). Anselm had prayed for a single, short argument by which to prove almost everything about God. The result was a simple deductive argument.

Deductive Arguments

A deductive argument is one where the conclusion necessarily follows from the premises – if the premises are true then the conclusion must follow. For example we could put forward the premise that:
  1. A bachelor is an unmarried man
  2. George is an unmarried man
  3. Therefore, it can be deduced that George is a bachelor
Providing premises (1) and (2) are correct then the conclusion (3) must necessarily follow. The validity of a deductive argument depends upon its internal logic – i.e. the very definition of words determines whether or not the argument can hold to be true.

Inductive Arguments

The opposite of a deductive argument is an inductive argument. Inductive arguments are based on observation.
  1. Jo, Charmaine, Kate, Lauren and Sarah wear skirts
  2. Jo, Charmaine, Kate, Lauren and Sarah are women
  3. Therefore, all women wear skirts

The validity of inductive arguments can vary from 0% to 100% as they are based on empirical observation and not internal logic. Premise (1) and (2) may well be true but the conclusion (3) may well be a massive assumption.

A priori vs. a posteriori

A deductive argument can be said to be ‘a priori’ as it does not depend upon external validation. The validity of a deductive argument can be ascertained before empirical validation. Because of their internal logic deductive arguments appeal to many philosophers c.f. Immanuel Kant’s ‘Categorical Imperative’.


The term ‘ontological’ is derived from the Greek ‘onto’ meaning ‘being’ and ‘logos’ meaning ‘the study of’. In philosophy ontology is a branch of metaphysics. The ontological argument is so called because it deals with the very being of God.

Anselm’s Argument

Anselm’s first form of his argument follows:
  1. God is the greatest possible being (nothing greater can be conceived)
  2. If God exists in the mind alone (only as an idea), then a greater being could be imagined to exist both in the mind and in reality
  3. This being would then be greater than God
  4. Thus God cannot exist only as an idea in the mind
  5. Therefore, God exists both in the mind (as an idea) and in reality.
The first premise (1) that God is the greatest possible being stems from the classical attributes of God i.e. omnipotence, omnipresent, omniscience…etc. It naturally follows that there cannot be two rival omnipotent beings…etc. For Anselm (and most theistic thinkers) this understanding of God goes without saying. It is axiomatic to say that God is omnipotent…etc. Any other definition of God would not be God.

The second and third premises (2 and 3) argue that something that exists in reality is better than something that exists only in ones imagination. For example, which is better imagining that you have £1 million, or actually having £1 million in your bank account?

The conclusion (4) follows from the first three premises (1,2 and 3). Anselm’s final conclusion (5) is that if all the previous premises are true (1,2,3 and 4) then God must exist.

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