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Quoting SEP:

Version A:

  1. Whatever I clearly and distinctly perceive to be contained in the idea of something is true of that thing.

  2. I clearly and distinctly perceive that necessary existence is contained in the idea of God.

  3. Therefore, God exists.

Version B:

  1. I have an idea of supremely perfect being, i.e. a being having all perfections.

  2. Necessary existence is a perfection.

  3. Therefore, a supremely perfect being exists.

How can I convert it to first-order logic? Furthermore, how can we test for the validity of the rule of inference?

Edit: How sound is the argument?

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They are both simple variations on Modus Ponens, and I don't think that anybody questions that the inferences are valid; what is at stake is whether or not they are sound.

EDIT:

The general consensus is that the arguments are not sound; there is no particular reason to believe that "necessary existence is a perfection", or that "perfections" are even an appropriate concept here: does it make sense to conceive of a perfectly large (i.e., largest) integer?

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  • I edited the question appropriately.
    – user1207
    Commented Dec 22, 2011 at 9:01

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