Is there a limit set to human reason, where the mind must halt its inquiries without assuaging its perplexity? For rabbinic tradition, there is a limit; and a rabbi especially ought not to challenge the orthodoxy that governs Jewish religious belief. The legendary Rabbi Elisha ben Abuyah sought the certitude of reason, overstepped the limit—“Free reason . . . is a heady wine”—and was castigated a pariah. But was he? Milton Steinberg’s As a Driven Leaf elicits a far more sympathetic intellectual and emotional response to Elisha, the man, and his quest, pressing us to interrogate the limit of faith and reason.