I think you are mis-stating the Atheists case.
I dont think the Hard Atheist believes that God’s existence is necessarily impossible, but instead believes that God’s existence is necessarily unproveable.
I’ve tried to read the ‘logical proof’ threads and posts, but I had to stop as my brain started to melt; maybe I’m not normal (or not logical).
I don’t think a logical proof of the necessity of God carries any more weight than a logical proof of the impossibility of God (you know the ones; 'if God carelessly left his immovable object in front of the garage door, would he still be able to park the irresistable force at night?")
nicky, I think you’re conflating atheism and agnosticism. The links I’ve provided may be helpful to you.
Mangetout, I agree. (With your assessment of logical proofs, not the assessment of your ‘normalcy’. My brain started to vapor lock over that ontology thread as well.) 
Xenephon, point taken. In fact those definitions would have been very useful a few days ago!
Now all we need is a definition of a true Scotsman.
Tris
If enough mumbo-jumbo in the form of “symbology” and abstract concepts like “modality” are used, anything can be confusing.
Libertarian starts with a definition of God as follows: "God as the “greatest possible perfection.” Now it seems to me that for that definition to have any validity at all there has to be the implicit assumption that the thing being defined does, in fact, exist.
The postulate from which his “proof” follows is: " If God (on the definition above) exists, He exists necessarily."
For the life of me I can’t see why this isn’t begging the question. I.e the proof starts with a definition that assumes the existence of the thing that the proof is supposed to prove exists.
At least with respect to the proof being discussed in the other thread, it isn’t really proving anything all that exciting - it certainly isn’t proving what Lib would have liked it to prove.
God is as perfect "as possible"
This is a key constraint on the nature of “God” in this proof. When you get right down to it, the “as possible” qualifier means that “God” is being defined as the most perfect being that there is. This isn’t really all that earth-shaking. If you take any non-empty set of things, one of them will be the “most perfect.” If the set of things is “everything” then one thing will be “as perfect as possible.”
In for a penny, in for a pound
If you accept a number of necessary premises and constraints (many of which are arguable but not unreasonable), this proof allows you to prove the existence of “God” as defined. However, this proof also allows you to prove the existence of any number of “demi-gods” who are really very much like “God.” (To avoid this, Lib would have liked to add a new axiom to this particular proof. However, his new constraint strikes me as both arguable and unreasonable.) Obviously, proving the correctness of the Hindu world view is not what most people have in mind when they advance these sorts of arguments.
If the “God” of this proof is “God,” the God of the Bible isn’t.
This proof necessarily posits a “God” with no subjectively defined attributes. This “God” is as perfect as possible – this being has every attribute that necessary and no attribute that is not necessary. This “God” is defined by objective criteria only. “God” is omnipotent. However, “God” does not have the best taste in clothes. “God” has no taste in clothes because there is no objectively definable “perfect” taste in clothes. In other words, this “God” has no subjective characteristics. Bottom line – this “God” has no personality. Rather, this “God” is more like a machine or a force of nature. I doubt if any religion wants to lay claim to this conception “God.”
The real value of these proofs isn’t what the “prove.” It’s in the steps you have to go through in dealing with them. I doubt if anyone, even Lib, really believes this proof “proves” anything. However, anyone who tries to sort through it comes away with a better understanding of the questions even if they don’t get any answers.
David,
I find your post to echo some of my own hesitations for this argument. I don’t think your characterization is entirely on point, but it is on the same target circle as I mentioned above.
I usually feel like counting my change just before the therefore statement, in formal logical arguments. This time, I found myself checking my purse right after the definitions. I don’t think your statement that existence is implicit in the definition is quite right, but I am not quite sure it is wrong, either. I don’t know how much I paid, or how much I had on me, so I can’t say for sure that I was shortchanged. But I don’t feel like I heard enough argument to have had a proof. Silly objection, but there it is.
When you come in the door believing in God, without proof, you hardly qualify as a dispassionate judge, though.
Tris
I don’t begrudge you your opinion, though it is a bit tacky unless you will concede that all things using symbology and modality are mumbo-jumbo. Like computer programs, for instance.
It doesn’t say “the greatest perfection in existence”. If it did, there would be no proof needed. What is merely possible might not exist in all possible worlds.
But that is simply obvious. The greatest possible perfection exists in all possible worlds. (Do you disagree?) Whatever exists in all possible worlds exists necessarily.
But it doesn’t, as I explained. It assumes the possibility that it might exist.
That’s a necessary assumption in any ontological proof, because you cannot show that something is impossible without first conceding that it might be possible. Denying possibility altogether categorically results in the contradiction that something has been negated when nothing is there.
I agree with you there. In fact, the modern rewording of Anselm’s definition is almost mundane.
Well, it’s what Hartshorne had in mind with his insistence that the ontologically proven God must be panentheistic.
And just for the record, I didn’t want to add a new axiom, but merely amend the first so that it was biconditional. (It is rendered that way in other otherwise identical proofs.) And I still don’t know to this day whether Tisthammer used a horseshoe or triple lines. No one ever answered me.
But you’re wrong about the “demi-gods”, as you and I hashed out repeatedly over there. A subset of all perfections is no more what that proof is talking about than a toaster oven.
Now you’re stepping far outside and away from the proof. It makes no commentary on the nature of God beyond His mere existence. A conclusion that He is therefore somehow sterile and without personality is an irrelevant non sequitur.
Do logical proofs of god mean anything? In a way, but not the way people want to use them. Logical proofs are just a way for people to excercise their ability to use words. Words are only symbols, not things themselves. Anything you “prove” using symbols, you can also disprove with symbols. So what you are left with is a better understanding of, and greater expertise in using symbols.
What two-faced nonsense. Can you prove with symbols that the square root of 2 is a rational number? It is remarkable how the use and manipulation of symbols is proudly displayed to show how hydrogen mixes with oxygen, but pooh-poohed when they show that God exists.
Oh, I know. You will protest that H[sub]2[/sub]O symbolizes a practical thing. And yet you cannot say. without faith that you fully comprehend the nature of reality, that what it symbolizes is not trivial. Not if the source of life itself is G.
Stop applying double standards whenever they suit you.
I did not apply any double standards, and I find it interesting that you would accuse me of doing so. Actually, your post has just showed me another reason why your “proof” is hopelessly wrong. You are arguing that the symbols are in fact meaningful. But as I said and you could not even attempt to refute, the symbol and the real thing are not the same. Therefore, if you define G as the greatest possible perfection, you have just disproven a real god! Because if the symbol of god is the greatest perfection, there can be no greater perfection - not even a real, existing god. As an example, think of a symbol for “circle.” This symbol is absolutely perfect, by definition. The symbol includes all possible circles that we can imagine. It is more perfect than any circle that actually exists. In the same way, your symbol for god is the greatest perfection, and cannot be outdone by a single real god. Therefore if anything you have proved the nonexistence of god, but I will assume that was not your intention and just say that you have proven nothing.
Libertarian, you said:
"Now you’re stepping far outside and away from the proof. It makes no commentary on the nature of God beyond His mere existence. "
If it doesnt make any commentary on the nature of God, what use is it?
Whats the difference between:
Believer 1)
- accepts ontological argument
- makes leap of faith to accept Christianity
Believer 2
- makes leap of faith to accept Christianity
Or even between
“Atheist” 1)
- accepts ontological argument
- makes leap of faith that God does not intervene and mans existence is purely material. So in practice is an atheist.
Atheist 2)
- ignores/rejects ontological argument, doesnt believe in God
Like any ontological discovery, it gives you a place to start. Look what Cantor did with infinity! 
Tisthammer’s proof does not ask anyone to leap to any sort of faith. It is not a substitute for faith. It is merely a common sense assessment of whether God exists. Such knowledge is hardly faith. Even some of the people who concede the validity of the argument call it “meaningless” or otherwise shrug it off.
A discussion of faith is off-topic here.
[…blank stare…] Um, the letter “G” is not defined as the greatest possible existence anymore than the letter “H” is defined as having one proton and one electron.
Really? Those who own a horse and draw one on its saddle will disagree with you.
This kind of “proof” is only convincing to those who are already convinced - or no philosophers would be atheists. Have you ever heard of someone who became a believer because of a logical proof of God’s existence?
One problem with them is that they don’t tell you much about the nature of the God whose existence is being proved. “Most perfect being”, OK, but perfectly good or perfectly evil? Perfectly powerful, or perfectly powerless? Perfecly huge? Perfectly godawful? You won’t find the answers in this “proof”.
There’s no point in the “quotation marks” unless you can show a sufficient flaw in the proof to debunk it. (A few people make a weak, but not uninteresting case about the application of Becker’s postulate, for example.) I take your point about the philosophers, but the proof is quite modern. Modality was first applied to revisions of Anselm’s (and others’) work in the late 20th century. At least give it time to circulate.
Meanwhile, you’re right that it doesn’t say much about the nature of God. In fact, it says nothing at all about that. Perfection is not a description of His nature, but of His existence. At any rate, you may not assign negative statements as attributes of that description because they would create modal contradictions, unless you are willing to define evil and impotence as great and their opposites as without ontological significance. And speaking of philosophers, that would put you in a tiny little corner practically by yourself. You won’t even find many atheists there.
The fact that ontological validity is entirely different from belief, or faith is not a logical refutation of this proof, or even ontological analysis itself. The matter of knowing God is not amenable to logical analysis. The objections offered, including my own, I must admit, are objections to relevance outside of ontological analysis. The bear does indeed dance. That I prefer a polka, and don’t like bears anyway may be important to me, but it has no validity in the matter of whether the bear dances.
Keep in mind that all your favorite “well known scientific facts” were also examined in this way, and the practice of good analytic methods is a part of all philosophical endeavor. No, it doesn’t mean that you are compelled to worship Anslem’s God. It means that you have to eschew the observation that religious belief is inherently illogical. That premise is demonstrated to be unfounded.
You can still ridicule specific religions, if you choose, of course. We wouldn’t want to take that away from anyone.
Tris
We seem to have wondered very, very far afield from the OP.
I take jayjay’s OP to ask, “Does a purely logical arguement about God’s existence” have any practical (meaning “utilitarian”) value, or is it merely an intellectual excercise?
Restating the original arguements in the other thread isn’t getting at what jayjay appears to have asked.
As Joan Rivers (who got her degree in Philosphy) once said, “All that enabled me to do was go to the butcher and argue about the existence of the brisket I was about to buy.”
FriendRob, I think that’s a little harsh. Philosophers are convinced by all sorts of rational proofs. In fact, I should say that if one came down the line which proved god exists a priori a great many would feel compelled to jump on the bandwagon. Of course, the a priori formulation which proved it must be acceptable to begin with, and it is difficult to say that a priori formulations are not begging the question since they are essentially tautological in nature (strict deduction from explicit axioms).
Tris, there are some theists who have posited that there is no logical description of God because God is completely unique. There is nothing “like” God, and so God cannot be contained or even adequately expressed in any symbol set since such symbol sets require a certain bit of universiality to them. One such man who felt this way, you may or may not be surprised to hear, was the oft-cited but rarely understood William of Ockham.
Lib, some logicians have taken propositions that are necessarily true to be propositions that say nothing about the world. Though, I suppose, you probably knew that. I have not decided yet whether I feel that such analytic expressions do or do not say anything about the world. Sometimes it seems absurd to say they don’t, sometimes it seems absurd to say they must. 