“Every year one of my cousins tries to derail the seder by insisting that the story of the Exodus never happened so we shouldn’t talk about it like history. How can I turn this into a productive discussion at the seder?”
I would head your cousin off at the pass. Speak to him or her before the seder. Explain that you would like to have a productive discussion at the seder, and invite him/her to come up with a few constructive suggestions how you might achieve that.
But your cousin has a point. There is, in fact, scant historical evidence that the Exodus ever took place. I can understand your cousin being frustrated by folks discussing even an important, powerful, and dramatic event like the Exodus as if it necessarily actually took place as described in the Book of Exodus. (In fact, it isn’t precisely clear what is meant by “as described in the Book of Exodus.” For the Bible presents several different versions of just about every important event it describes, and the Exodus is no different. For example, read the Book of Exodus chapters 14 and 15. You will be hard-pressed to create from those two chapters a seamless, chronological account of the crossing of the Red Sea.)
The fact is, the historicity of the tale that we tell and re-tell on Pesach (Passover) is not essential to the significance it plays in our collective consciousness. Rather, the philosophical and moral lessons that the story is designed to impart are the key.
Those lessons are timeless and do not depend on the precision or accuracy of the biblical account. If this is surprising to you, you and your cousin might benefit from two books: How to Read the Jewish Bible by Marc Zvi Brettler and How to Read the Bible: A Guide to Scripture, Then and Now by James Kugel, especially the chapter on the Exodus. You might also want to learn about the famous sermon that Rabbi David Wolpe delivered at the Sinai Temple in Los Angeles in 2001, in which he argued this point. He condensed it into an article in 2004. You might also be interested in the brouhaha that arose following Rabbi Wolpe’s sermon.
Judaism, as Yosef Hayim Yerushalmi has demonstrated (see Zakhor: Jewish History and Jewish Memory), is a religion of memory, not history. The key to our faith is how we remember our past, and how we interpret it—rather than what “really happened.”
To put it bluntly: I don’t know whether the Israelites were ever in Egypt; I don’t know whether there ever was an Israelite named Moses who was raised as an Egyptian and who later identified with his people and helped them escape from slavery. I know none of these things, and yet, I know them all to be true—in a religious, rather than a historical, sense. Indeed, it is absolutely “true and certain” to me that, in a religious sense, my ancestors were slaves to Pharoah in Egypt and were redeemed with a strong hand and an outstretched arm. And for that reason, I feel called upon to eat bitter herbs and matzah while telling and re-telling that story each and every year.
I wouldn’t waste my breath trying to defend the historicity of the biblical account of the Exodus. Instead, I would try to engage your cousin—and the others sitting around the seder table—in a discussion of what the story can teach us about human freedom and the challenges we all face, even today, living as we do in a world in which human degradation and even slavery still exist. How many of us sitting around the table—perhaps even your cousin—are wearing clothing, eating food, or making use of electronic devices that were produced with the help of exploited workers? (Perhaps we should put a smart phone on the seder plate alongside the charoset.)