I've been reading through Joshua lately. When I got to the Gibeonite episode in chapter 9, I noticed something that I don't think had ever registered with me before. Several other examples have since occurred to me.
In Joshua, Israel had a divine mandate to carry out: God's judgment on the Amorites declared all the way back in Genesis 15. I think most Biblical scholars take the Genesis 15 reference to include all the people living in the land, not just ethnic Amorites, just as later texts use the term 'Canaanites' to refer to all of the people, even though several lists include Amorites and/or Canaanites among lots of other names (Hivites, Girgashites, Jebusites, Hittites, Perizzites; no list actually has exactly the same combination in the same order).
The Gibeonites were part of that mandate, but they deceived Israel into thinking they were from a far-away land and had come to Canaan to make a covenant with Israel to protect them. Israel bought the deception and made the covenant.
What I hadn't noticed before is that the text seems to assume Israel's responsibility to keep that covenant, even given the deception. It's common nowadays to assume that a promise is void if it's made under false pretenses, because your words didn't apply to exactly the thing you thought you were agreeing to. If I promise to pay off a debt you have that you tell me you accrued due to an oppressive landlord's cruel policies, and then I later discover that you have the debt merely because of gambling, the idea is that I don't have any obligation to pay the debt for you, because I didn't agree to pay off a gambling debt. I only agreed to pay off a debt caused by an unjust landlord. I know of one philosophical paper on the subject of consent that argues that someone hasn't given voluntary, informed consent to sex if they've given explicit consent but the person had been hiding the fact that the two were close relatives, because giving consent to sex doesn't amount to giving consent to incest if you don't know the person is a close relative and the other person does.
I'm seeing a several biblical accounts that seem to assume a contrary position. The Gibeonite case is just one instance among a few that have occurred to me, but it's a particularly vivid example of how fully in force this covenant is, even generations later, even to a king who had no idea that it was being violated until he inquired of God. By II Samuel 21, Israel's failure to keep that covenant in Saul's time (Saul had tried to wipe the Gibeonites out) had led to God causing a three-year famine as judgment. David, in his ignorance, was facing the famine in the kingdom as a consequence of not keeping that covenant. The covenant was made in ignorance, and it was continuing to be broken in ignorance, but that did not exempt Israel from their obligation to it. David was even ignorant of the cause of the famine, but he still bore responsibility for dealing with it. David remedied the problem and honored the covenant.
I can think of several other instances just in the book of Genesis. In Genesis 12, Abram visits Egypt and says that his wife Sarai is his sister (which he later says is technically true; see Gen 20:12, but it's still deception). Pharaoh gets upset when he discovers the deception, because he could have married her and thus married another man's wife. Even if he had done so in ignorance, the reason he gives for his outrage is that Abram could have caused him to sin ignorantly. A similar circumstance occurs later in Abraham's life in Genesis 20 but with Abimelek the king of Gerar instead of Pharaoh. A third instance of the same fault occurs with Abraham's son Isaac in Genesis 26, who also faces a similar situation with someone called Abimelek the king of Gerar (not necessarily the same figure, since it could be a title like 'Pharaoh'). It's possible in these cases that it's just an ethical framework shared by the Hebrews, Egyptians, and Gerarites. If so, it doesn't mean someone holding to the authority of scripture would have to say that God endorses it. It's the words of the Pharaoh or Abimelek that assume the principle.
But in Joshua and the subsequent Samuel text, it seems harder to say that. I think the narrator more clearly endorses the principle there. That also seems to me to be true of a couple more cases in Genesis, involving Jacob. First, In Genesis 27, Jacob deceives his father Isaac into giving his blessing to him rather than to his older twin brother Esau, who would normally have received it. Since this was not just a father's blessing but a passing on of the blessing bestowed on Isaac via the covenant with Abraham, there was only one blessing of this sort to give, and Isaac recognized that once the blessing was given, he'd passed on what had been entrusted to him by God. He couldn't undo it. That sacred trust had been given to Jacob now. The narrator seems to assume that as much as Isaac does when he explains to Esau that he can't now give his blessing to him also.
Then Jacob gets a taste of his own medicine. In Genesis 29, his uncle Laban made an agreement with Jacob that he could marry his daughter Rachel, but Laban deceitfully sent his older daughter Leah to Jacob as his wife, veiled in a way that he couldn't recognize her. The assumption of the text and of all parties involved is that Jacob had in fact married Leah, not Rachel. Laban then, in an act of further shadiness, made Jacob work for seven more years (he'd already worked his agreed-to seven years) in exchange for getting to marry Rachel too. But even crooked Laban recognized that he had in fact promised Jacob Rachel, and so he allowed him to marry her as soon as the deception had been exposed, with the condition of working seven more years in exchange. So Laban did give Jacob what he'd promised, even if the deal was twice made crooked. But the assumption is that Jacob had married Leah, even if he had done so not knowing who he was marrying.
I do think someone could try to argue that there are contextual differences in how different cultures see vows and agreements, and in the ancient near east this is the assumption, whereas we have different ones now. So given their interpretive framework, vows and covenants mean something to them that we wouldn't import to them now, and the condition of deceit didn't exempt them given their cultural assumptions, whereas it would exempt us. That's what I think someone with a high view of the authority of scripture's moral teaching would have to say to maintain the popular conception that deceit on the part of another party exempts someone from a vow. I wonder if that's a bit of a stretch, though, because presumably the conditions of how promises are interpreted can be contextually-sensitive in different cultural environments, but can exempting factors be that way? We're not talking about the conditions of when a promise means one thing and when it means another. We're talking about when you're morally obligated and morally exempt. That doesn't seem to me to be the sort of thing that I would expect to be culturally relative.
I do think the defender of the popular view can try to find a middle ground more easily. Perhaps there are some circumstances where ignorance excuses or absolves, and there are others where it doesn't. That's probably true, I would say. The question is whether we can come up with a criterion for why some would be and not others. It would have to be a justifiable criterion on grounds independent of trying to find some principle designed to get the answers you want on both kinds of cases. But I'm open to that as a real possibility. I'm not quite sure what to think about this beyond that, though.