In the past I've said that the Ontological Argument for God's existence is fundamentally flawed, but now I'm not so sure. It is easy to misunderstand the argument because it is pure logic, and if it is misunderstood then it seems nothing more than a word game, but if properly understood it is formidable. I'm sorry for this very long thread, but I'm floating a couple of thought-balloons here, without knowing exactly how they will turn out.
I'll try to explain it easily. Here is the skeleton of the proof:
1) The idea of God as a maximally-great-Being is possible.
2) A maximally-great-Being is a necessary being
3) A necessary being exists in all possible-worlds
4) The extent world (this world) is a possible-world
5) Therefore, God is either necessary or impossible
6) The existence of God is not impossible (see premise 1)
7) Therefore, God in some possible world.
8) A necessary being exists in all possible worlds.
9) (re-stated) The exent world is a possible world
10) Therefore, God exists in the extent world.
There are a number of terms that must be defined for this to make sense:
Possible-world: this just means "a way that the world could have turned out." It does not mean that these hypothetical worlds exist, only that they are possibilities which are not excluded by logical-inconsistencies.
Extent world: The really-existing world (id est, this world).
Necessary thing/being: Something that is described as necessary is something which must exist in all possible worlds. An example is mathematical facts such as 3 + 2 = 5. There can be no possible world where adding 3 of one thing to 2 of the same gives you anything but 5 of that thing.
Impossible: Something which is logically-contradictory (e.g. Judechild draws square-circles in his free time). Things that are impossible cannot exist in any possible world.
Maximally-great being: A being which possesses all things that it is better to have than not to have, and possesses them to the maximal extent.
Here, then, is a little narration that I've developing to explain it:
Imagine you are in a round, vaulted room with thousands of shuttered windows. In the middle of the room is a pedestal with the words "Each opens onto a possible-world" written on it. Curious, you unlatch one of the windows, and remove the shutter. You see in this world that air particles reflect red light, and so the sky is red. You try another; in this world, the Earth is much more massive - but still supports life - and so the animals all have thicker bones to deal with the increased gravity. You look into a third and find unicorns, knights, and people who can tap into some metaphysical force which they can use for medicinal or aggressive purposes. You continue to try several other windows.
But no matter how many possible worlds you look on to, you realize that there are some properties which are common to all possible-worlds. In one of the worlds, you see a woman trading at a market. She is holding two apples and she asks the merchant for three more. He gives these to her, and you count that she now has five apples. In another world, you see the same scene, even though the surroundings are very different, and the "apples" are blue and flat; still, when the woman asks for three apples to add to her two, you count five apples. The same happens in a third world, only this time the fruit is much smaller and perfectly round. You also notice that time progresses: past, present, future, in relation to the material of the world. Finally, you notice that in many cases there are people standing and there are people sitting, but in no world can one of these people both sit and stand at the same time, and in the same respect. From these considerations, you come to distinguish between the possible, and the necessary; the possible is any way that the world could be and as such is not common to every possible-world, but the necessary, you reason, is common to all possible worlds and any world that does not have one of these necessary principles is not possible - but impossible.
As you back away from the windows which look out on possible-worlds, you notice a second inscription on the pedestal in the center of the vaulted room. You pick out the words "Is God possible?" As you ponder this, a woman approaches who introduces herself as the curator. She asks you what your answer to the question is. You don't feel the need to dispute the claim at the moment, and so you say "yes." The Curator says, "then God exists - hypothetically, mind you - in at least one of these possible-worlds?" Remembering that even things which do not exist in the extent world - such as unicorns and wizards - exist in at least one of the possible-worlds, you agree that it is hypothetically true. "Now, if something exists in one possible world, and it is necessary, what do we know?" You respond that it would follow that a necessary thing that exists in one possible world must by definnition exist in all possible-worlds; like 2 + 3 = 5, which, because it exists in a possible world and is necessary also exists in all. "Then, if God exists in a possible world, and He is necessary, then we have proven that He exists in all possible-world; correct?" You nod. "And the extent world is a possible-world?" Again, you nod. "Then" the Curator finishes, "if God is necessary, then He must exist in the extent world."
"How then, do we know that God is necessary?" you ask. In response, the Curator hands you a pen and paper, and then tells you to draw a triangle with four sides. You respond that you cannot. She tries again, ordering you to draw a triangle whose interior angles do not add up to one-hundred and eighty degrees. Again, you say that you cannot. "That is because," the Curator explains, "those properties are intrinsic to the concept of a triangle. The same applies to God, there are properties which are intrinsic to His concept. One of these properties is that He is Maximally-Great. A Maximally-Great Being possesses all properties which it is better to have rather than not to have, and possesses them to the maximal extent. This means that the Maximally-Great Being possesses the maximum of intelligence, compassion, love, benevolence, et cetera. Now, is it greater to exist or not to exist?" You respond that it is greater to exist. "That is correct, and so we cannot speak of a Maximally-Great Being who does not exist, because a Maximally-Great Being includes "existence" in its concept. We can only say that the Maximally-Great Being is impossible (that is, that He can exist in no possible-world), or that He exists necesarily (because existence is within His ontology); to say 'a Maximally-Great Being does not exist' is to say 'A Maximally-Great Being who is not a Maximally-Great Being does not exist' - and that is nonsense; it would be like saying 'I see a triangle with four sides.' How did you respond when I asked if God's existence is possible again?"
The conclusion seems inevitable, since God's existence is possible, and therefore He exists in a possible-world - and His existence is necessary, and therefore if He exists in one possible-world He must exist in all - it is the logical conclusion that God exists in all possible-worlds. Since the extent world is a possible-world, it then naturally follows that God exists in the extent world as well. The Curator leaves you as you return to the extent world, to tell Judechild what you think of all this.
I'll try to explain it easily. Here is the skeleton of the proof:
1) The idea of God as a maximally-great-Being is possible.
2) A maximally-great-Being is a necessary being
3) A necessary being exists in all possible-worlds
4) The extent world (this world) is a possible-world
5) Therefore, God is either necessary or impossible
6) The existence of God is not impossible (see premise 1)
7) Therefore, God in some possible world.
8) A necessary being exists in all possible worlds.
9) (re-stated) The exent world is a possible world
10) Therefore, God exists in the extent world.
There are a number of terms that must be defined for this to make sense:
Possible-world: this just means "a way that the world could have turned out." It does not mean that these hypothetical worlds exist, only that they are possibilities which are not excluded by logical-inconsistencies.
Extent world: The really-existing world (id est, this world).
Necessary thing/being: Something that is described as necessary is something which must exist in all possible worlds. An example is mathematical facts such as 3 + 2 = 5. There can be no possible world where adding 3 of one thing to 2 of the same gives you anything but 5 of that thing.
Impossible: Something which is logically-contradictory (e.g. Judechild draws square-circles in his free time). Things that are impossible cannot exist in any possible world.
Maximally-great being: A being which possesses all things that it is better to have than not to have, and possesses them to the maximal extent.
Here, then, is a little narration that I've developing to explain it:
Imagine you are in a round, vaulted room with thousands of shuttered windows. In the middle of the room is a pedestal with the words "Each opens onto a possible-world" written on it. Curious, you unlatch one of the windows, and remove the shutter. You see in this world that air particles reflect red light, and so the sky is red. You try another; in this world, the Earth is much more massive - but still supports life - and so the animals all have thicker bones to deal with the increased gravity. You look into a third and find unicorns, knights, and people who can tap into some metaphysical force which they can use for medicinal or aggressive purposes. You continue to try several other windows.
But no matter how many possible worlds you look on to, you realize that there are some properties which are common to all possible-worlds. In one of the worlds, you see a woman trading at a market. She is holding two apples and she asks the merchant for three more. He gives these to her, and you count that she now has five apples. In another world, you see the same scene, even though the surroundings are very different, and the "apples" are blue and flat; still, when the woman asks for three apples to add to her two, you count five apples. The same happens in a third world, only this time the fruit is much smaller and perfectly round. You also notice that time progresses: past, present, future, in relation to the material of the world. Finally, you notice that in many cases there are people standing and there are people sitting, but in no world can one of these people both sit and stand at the same time, and in the same respect. From these considerations, you come to distinguish between the possible, and the necessary; the possible is any way that the world could be and as such is not common to every possible-world, but the necessary, you reason, is common to all possible worlds and any world that does not have one of these necessary principles is not possible - but impossible.
As you back away from the windows which look out on possible-worlds, you notice a second inscription on the pedestal in the center of the vaulted room. You pick out the words "Is God possible?" As you ponder this, a woman approaches who introduces herself as the curator. She asks you what your answer to the question is. You don't feel the need to dispute the claim at the moment, and so you say "yes." The Curator says, "then God exists - hypothetically, mind you - in at least one of these possible-worlds?" Remembering that even things which do not exist in the extent world - such as unicorns and wizards - exist in at least one of the possible-worlds, you agree that it is hypothetically true. "Now, if something exists in one possible world, and it is necessary, what do we know?" You respond that it would follow that a necessary thing that exists in one possible world must by definnition exist in all possible-worlds; like 2 + 3 = 5, which, because it exists in a possible world and is necessary also exists in all. "Then, if God exists in a possible world, and He is necessary, then we have proven that He exists in all possible-world; correct?" You nod. "And the extent world is a possible-world?" Again, you nod. "Then" the Curator finishes, "if God is necessary, then He must exist in the extent world."
"How then, do we know that God is necessary?" you ask. In response, the Curator hands you a pen and paper, and then tells you to draw a triangle with four sides. You respond that you cannot. She tries again, ordering you to draw a triangle whose interior angles do not add up to one-hundred and eighty degrees. Again, you say that you cannot. "That is because," the Curator explains, "those properties are intrinsic to the concept of a triangle. The same applies to God, there are properties which are intrinsic to His concept. One of these properties is that He is Maximally-Great. A Maximally-Great Being possesses all properties which it is better to have rather than not to have, and possesses them to the maximal extent. This means that the Maximally-Great Being possesses the maximum of intelligence, compassion, love, benevolence, et cetera. Now, is it greater to exist or not to exist?" You respond that it is greater to exist. "That is correct, and so we cannot speak of a Maximally-Great Being who does not exist, because a Maximally-Great Being includes "existence" in its concept. We can only say that the Maximally-Great Being is impossible (that is, that He can exist in no possible-world), or that He exists necesarily (because existence is within His ontology); to say 'a Maximally-Great Being does not exist' is to say 'A Maximally-Great Being who is not a Maximally-Great Being does not exist' - and that is nonsense; it would be like saying 'I see a triangle with four sides.' How did you respond when I asked if God's existence is possible again?"
The conclusion seems inevitable, since God's existence is possible, and therefore He exists in a possible-world - and His existence is necessary, and therefore if He exists in one possible-world He must exist in all - it is the logical conclusion that God exists in all possible-worlds. Since the extent world is a possible-world, it then naturally follows that God exists in the extent world as well. The Curator leaves you as you return to the extent world, to tell Judechild what you think of all this.