I am not trained in formal logic, so I was hoping you could help me with the moral argument for the existence of God, postulated as follows: 1. If God doesn't exist, then objective moral standards don't exist. 2. Objective moral standards exist. Therefore God exists. I don't really understand why the arguer is allowed to throw in premise 2. It seems that in order to prove that objective moral standards exist, you must first prove that God exists (because the objective moral standards come from God). Since the truth of premise 2 depends on the conclusion of the argument, it seems the argument collapses into a circle. I guess what I'm really saying is that any theist I know would concede that premise 1 is actually an if and only if statement (again, because morality is inextricably linked with God). After all, if you could prove that objective moral standards exist without appealing to God, then you've demonstrated morality's independence from the existence of God and thus nullified the argument. I think the argument fails for other reasons, but is this particular criticism valid? Thanks for your time.

Although I think the argument is fraught with difficulties, I don't think it simply begs the question. Suppose this hypothetical theist -- call her Thalia -- is arguing with an agnostic, Agatha, who nonetheless believes that there are objective moral standards. Agatha has real-life counterparts, and some of them are even sophisticated philosophers. Suppose Thalia makes a case for premise one: that moral standards really do presuppose the existence of a divine lawgiver. At that point, Agatha has a choice: give up belief in objective moral standards, or take up theism. Depending on how convinced she is that there really are moral standards, she might well decide that she should opt for theism.

Notice that from Agatha's point of view, there's no need for proof that there are objective moral standards. She already believes that. What she'd need to be convinced of is that premise 1 is true. And although I'm personally skeptical of premise 1), I do think there's more to be said here than meets the eye (though that's a long story.)

What philosophers are up to in cases like this, I'd suggest, is looking for the most coherent, satisfying overall story -- with the story that does the most justice overall to our various convictions. The little syllogism you've formulated is a stand-in for a much more complex debate.

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