Can God be wrong?

1. The Bible says God cannot lie. Suppose an atheist challenges you: how do you know that's not a lie? How do you know God isn't lying when he says he can't tell a lie?

Likewise, God makes promises to his people: forgiveness and eternal bliss. But the atheist challenges you: how do you know that isn't a lie?

2. This has its pedigree in the Cartesian demon, as well as Steven Law's recent Evil God knockoff. Suppose Christians can't prove it? Suppose we don't know in advance if God is telling the truth? So what? We'll find out. If it's true, then we had everything to gain and nothing to lose. And if it's false, then there's no advantage in being an atheist. An evil God won't reward an atheist. If you're a dutiful devil-worshiper, that doesn't mean the devil will reciprocate your loyalty. 

3. However, let's take this a step further. The Cartesian demon knows the difference between truth and falsehood. Although he's a deceiver, he isn't self-deceived. 

But is it possible for God to be self-deceived? Is it possible for God to be confused? 

This isn't just hypothetical. In open theism, God entertains false beliefs about the future. If you take open theist prooftexts seriously, God has false expectations about the future. Sometimes things turn out contrary to what he anticipated. That's because the God of open theism is dependent on world events for his knowledge of world events. 

4. However, when we push the question to the limit, it raises the issue of what makes something true or false. What is the source and standard for truth and falsehood? Is that independent of God or dependent on God?

There are different kinds of truth: contingent, logical, counterfactual, mathematical, and modal (i.e. possibility, necessity, impossibility) truths. In Calvinism, these can all be grounded in God. Contingent facts refer back to predestination. Counterfactual truths refer back to God's ability to instantiate alternate possibilities. Logical, mathematical, and modal truths inhere in God's mind, aseity, omnipotence, and omniscience. 

Unless truths and truthmakers can exist apart from God, then even if (ex hypothesi) God deludes others, God cannot be self-deluded. So that establishes a floor for skepticism. It can't go all the way down. 

5. Taking it up a level, the question of whether God can deceive may depend on whether divine deception (if that's even possible) is motivated by malice or benevolence. In other words, inseparable from the question of divine goodness. 

And that, in turn, raises a parallel with (4). What makes something good? What is the source and standard of goodness? If good is dependent on God, then there can't be an evil God–unless goodness is an illusion. And it's unclear how goodness could be an illusion. How could evil be the ultimate reality if evil is asymmetrically dependent on good to provide the necessary point of contrast?

There are debates about whether lying is intrinsically wrong. If you think it's intrinsically wrong, then it's impossible for God ever to lie. If you don't think lying is intrinsically wrong, if there are circumstances under which lying is justifiable, then, in principle, God might sometimes lie, but never maliciously. 

Even if you think lying is sometimes justifiable for humans, there's the question of whether the considerations which make it justifiable for humans extend to God, since God is not under the same constraints as humans. But in any case, God cannot lie about his promises to his people because that would be the act of an evil God, a malicious deity. 

Admittedly, all I've done in this little post is to block out the issues and outline some argumentative strategies. It takes a lot of spadework to turn those into philosophically rigorous arguments. That's a research program for Christian philosophers. I will say that Greg Welty and James Anderson are doing yeoman work in this field, with special reference to modal metaphysics.