There are four basic categories of philosophical arguments for God’s existence. The one I find most compelling is the cosmological argument, which I have written about here and here. Gene Edward Veith (Cranach, another blog I read almost daily) points to a statement of the moral argument for God’s existence by William Lane Craig:
The moral argument. A number of ethicists, such as Robert Adams, William Alston, Mark Linville, Paul Copan, John Hare, Stephen Evans, and others have defended “divine command” theories of ethics, which support various moral arguments for God’s existence. One such argument:
1. If God does not exist, objective moral values and duties do not exist.
2. Objective moral values and duties do exist.
3. Therefore, God exists.
By objective values and duties, one means values and duties that are valid and binding independent of human opinion. A good many atheists and theists alike concur with premise (1). For given a naturalistic worldview, human beings are just animals, and activity that we count as murder, torture, and rape is natural and morally neutral in the animal kingdom. Moreover, if there is no one to command or prohibit certain actions, how can we have moral obligations or prohibitions?
Premise (2) might seem more disputable, but it will probably come as a surprise to most laypeople to learn that (2) is widely accepted among philosophers. For any argument against objective morals will tend to be based on premises that are less evident than the reality of moral values themselves, as apprehended in our moral experience. Most philosophers therefore do recognize objective moral distinctions.
Nontheists will typically counter the moral argument with a dilemma: Is something good because God wills it, or does God will something because it is good? The first alternative makes good and evil arbitrary, whereas the second makes the good independent of God. Fortunately, the dilemma is a false one. Theists have traditionally taken a third alternative: God wills something because he is good. That is to say, what Plato called “the Good” is the moral nature of God himself. God is by nature loving, kind, impartial, and so on. He is the paradigm of goodness. Therefore, the good is not independent of God.
Moreover, God’s commandments are a necessary expression of his nature. His commands to us are therefore not arbitrary but are necessary reflections of his character. This gives us an adequate foundation for the affirmation of objective moral values and duties.
Grace and Peace