St. Anselm of Canterbury (1033-1109):
The Ontological Argument For God's Existence

  1. Intellectual Background -

    1. Neoplatonism - Plotinus (204-270 CE)

    2. St. Augustine - (353-430 CE)

    3. Collapse of the (western) Roman Empire (476 CE)

  2. The Ontological Argument -

    1. Anselm's Definition: God is -

      "That than which nothing greater can be conceived"
      The greatest conceivable Being

    2. The Argument -

    Note: Two Modes of Existence:

    1. Potentiality - To be conceivable (i.e., to have the idea of X)
    2. Actuality - For some conceivable X to exist

    First Argument:

    P1. If we can conceive the idea ‘God‘, then God exists potentially.

    P2. We can conceive the idea 'God' (i.e., we understand the word 'God' when used).

    C1. Therefore, the idea 'God' exists in our understanding.

    P3. If 'God' exists in the mind alone, then we can conceive of a Being greater than 'God'.

    Note: To exist is greater than not to exist.

    P4. We cannot conceive of a Being greater than 'God' (by definition).

    C2. Therefore, 'God' cannot exist in our understanding alone.

    C3. Therefore, 'God' must exist both in our understanding and in reality.

    Second Argument:

    Note: Two Types of Actual Things:

    1. Contingent - any actually existing thing which could fail to exist, or be different than it is.
    2. Necessary - any actually existing thing which cannot fail to exist or be different than it is.

    P1. We can conceive of something existing necessarily or contingently (but not both).

    P2. Necessary things are greater than contingent things.

    P3. God is a necessary thing (by definition).

    C1. Therefore, if 'God' can be conceived to exist contingently, 'God' is not God.

    P4. It is a contradiction to assert that God is not God.

    C2. Therefore, we cannot conceive of God as a contingent being.

    C3. Therefore, God must be a necessary being.

    Objections -

    1. Gaunilo's Analogical Reductio: The Greatest Conceivable Island

    2. Rejection of Neoplatonic Metaphysics

      1. Why is actual existence greater than potential existence?

      2. Why is necessary existence greater than contingent existence?

    3. Emmanuel Kant - existential claims are synthetic not analytic

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