In this post, I will revisit Ernest Nicholson's The Pentateuch in the Twentieth Century. On page 234, Nicholson discusses John Van Seters' approach to the wife-sister stories of Genesis 12 and Genesis 20. According to Nicholson, Van Seters believes that the wife-sister story in Genesis 12:10-20 was an oral tradition, and that the author of the wife-sister story in Genesis 20 was addressing theological, moral, and plot problems that he had with Genesis 12. For example, why did God punish Pharaoh, when Pharaoh did not know that Sarai was Abram's wife? How did the Pharaoh even know that the illness that he and his household suffered was due to Sarai? Did Sarai sleep with the Pharaoh? And isn't it morally problematic that Abram lied?
In Genesis 20, Van Seters contends, there are answers to these problems. The king learned from God himself that God was displeased about what he was about to do with Sarah. In the process, God gave the king an opportunity to turn from his disastrous path. Sarah did not sleep with the king, for God prevented the king from touching her. And Abraham technically did not lie, for Sarah was his half-sister.
But Nicholson finds Van Seters' proposal to be problematic, for Genesis 20 does not solve all of the problems of Genesis 12. After all, Genesis 20 and Genesis 12 are presented in Genesis as two separate events. Genesis 12 has problems, and nothing that Genesis 20 says can change that, for Genesis 20 is not Genesis 12, or even a revision of it. Genesis 20 is about a different king altogether, the king of Gerar. The problems in Genesis 12 remain---except, perhaps, that, in light of Genesis 20, Abram in Genesis 12 did not technically lie about Sarai being his sister.
I plan to reread Van Seters' Abraham in History and Tradition to see what he argues, but I can somewhat understand how Genesis 20 can be seen as a correction of Genesis 12. Maybe we're supposed to assume that God acted in Genesis 12 as he did in Genesis 20: God told Pharaoh that his attempted adultery was wrong and kept him from touching Sarai. Nicholson quotes Samuel Sandmel, whose argument is that Genesis preserves Genesis 12 alongside Genesis 20 even though an editor had problems with Genesis 12: "The Abraham of Genesis 20 thus determines the character of the Abraham of Genesis 12:10-20)". For Sandmel, the editors were reluctant to expunge aggadot that they considered to be morally problematic, and so they included other aggadot that neutralized the morally problematic passages.