Wednesday, February 14, 2007

Ontological arguments

Some notes from today:

Anselms' argument, simplified.

He assumes that we (even "fool" atheists) have the concept of God, i.e., the idea of "the being who none greater can be conceived" i.e., thought. (Question: do we have such a concept? Is the concept coherent? Is a being like this possible? Perhaps not: perhaps

Here's the argument, simplified.

1. Either (a) "the being whom none greater can be conceived" exists only as a concept or an idea or (b) "the being whom none greater can be conceived" exists both as a concept and in reality.
2. To exist in reality is greater than to exist only as a concept or an idea. [see Anselm, end of 2nd paragraph, p. 71 of handout; Stairs premise 2, p. 82]
3. If (2) is true and if (a), the claim that "the being whom none greater can be conceived" exists only as a concept or an idea is true, then there exists a being greater than "the being whom none greater can be conceived."
4. But there cannot be a being greater than "the being whom none greater can be conceived," because that's a contraction.
5. So, (a) is not an option.
6. So, (b) "the being whom none greater can be conceived" exists both as a concept and in reality.
7. So, God exists, the being whom none greater can be conceived.

The basic logic:
1. Either A or B.
2. If B is true, then C is true.
3. But C is not true (because C is contradictory)
4. So, not B. (2, 3 Modus Tollens)
5. So, A. (1, 4, Disjunctive Syllogism).

Here's the argument from the Descartes' Fifth Meditation with a modifed translation:
If I can clearly and distinctly think the idea of something, then everything which I clearly and distinctly perceive to belong to that thing really does belong to it. "Certainly, the idea of God, or a supremely perfect being, is one that I find within me just as surely as the idea of any shape or number. And my understanding that it belongs to his nature that he always exists is no less clear and distinct than is the case when I prove of any shape or number that some property belongs to its nature." (AT 7:65; CSM 2:45).
So here's the argument:
1. If we can clearly and distinctly think the idea of something, then everything which we clearly and distinctly perceive to belong to that thing really does belong to it.
2. We can clearly and distinctly perceive the idea of God, or a supremely perfect being.
3. We can clearly and distinctly perceive that he always exists.
4. Therefore, since (1), (2) and (3) are true, God exists.

Here's an ontological argument commonly attributed to Descartes (but perhaps without textual evidence, since this is a bit different than the argument above?):

1. God is an all-perfect being.
2. An all-perfect being has every perfection (i.e., a great-making quality).
3. Existence is a perfection (i.e., a great-making quality; for something to exist makes it greater than for it not to exist: recall Anselm's "To exist in reality is greater than to exist only as a concept or an idea").

For discussion on Descartes' ontological arguments, see here:
http://plato.stanford.edu/entries/descartes-ontological/

Questions:
  • Are there reasons to think that any of the premises in these arguments are false?
  • Are there reasons to think that any of the premises in these arguments assume the conclusion they are supposed to support?
  • What about Gaunilo's objection that Anselm's argument can be used to "show" the existence of any "perfect" thing whatsoever (e.g., the island which none greater can be conceived, the tattoo needle which none greater can be conceived, etc.), and so is faulty? Are they any good?
Plantinga's Modal Ontological Argument:
next time!

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