Yirmiyahu Yovel opens The Other Within: The Marranos, his boldly speculative new book, with a story that falls into the category of truth stranger than fiction. Yovel writes that a friend of his, a graduate student who worked as a tour guide, once showed a party of Spanish tourists around the Cathedral of St. John the Divine in New York. He noticed that one of the men was murmuring a private prayer while making the sign of the cross, and asked what he was saying. “Oh, it’s an ancient custom in our family,” the Spaniard replied; so ancient, in fact, that when he said the syllables sakestesaksenu, he didn’t even know what they were supposed to mean. He only knew that his family were “devout Catholics, and on entering a church we say this special benediction as a sign of extra piety.”It took a little detective work by a Hebrew-speaking friend to realize that what the man was actually saying was “shakets teshaktsenu”—the phrase Moses uses, in Deuteronomy, when he commands the Israelites to hate idolatry. “The devout Spanish Catholic, as a sign of extra piety,” Yovel explains, “was repeating an ancient formula by which his Marrano ancestors used to curse and anathematize the church they were entering as a place of idolatry!”A story like this captures some of the strangeness of the Marrano phenomenon, but it is perhaps too bizarre—too much like something Dan Brown would build a best-seller around—to adequately represent the significance of Marranism in Jewish and Christian history. By the time this descendant of Spanish Jews made his curse/blessing, in the 20th century, he had well and truly forgotten his family’s connection to Judaism; “sakestesaksenu” was a purely vestigial holdover, a Jewish artifact accidentally preserved in Christian amber.But in the 15th, 16th and 17th centuries, Yovel contends, the Spanish and Portuguese Marranos—Jews and descendants of Jews who converted to Catholicism under legal pressure and physical threat—were much more than curiosities. They were nothing less than the vanguard of modernity—the first people to experience the fractured identity, social displacement, and spiritual homelessness that would become the universal European fate. Yovel assembles a whole catalog of “attitudes and patterns of the Marrano experience that pre-illustrate or anticipate main features and claims of Western modernization”: cultural and religious restlessness; the breakdown or mixture of legitimizing traditions; being at variance with accepted social modes, values, and routines; religious skepticism and heterodoxy; the rise of a secular urban culture; rationalism and universalistic tendencies.And the claims only get grander: Marranos invented or discovered nothing less than “private life,” “subjectivity and the inner mind,” “the Self and personal conscience.” Yovel seems to be offering a Jewish paraphrase of Descartes: Marrano, ergo sum.In order to justify such monumental claims, Yovel devotes most of his book to telling the history of the Marranos, and it is possible to learn a great deal from his narrative without sharing his ultimate conclusions. Yovel reminds us that the forced conversion of Spanish Jews to Catholicism began long before 1492; Ferdinand and Isabella’s infamous edict of that year, compelling the Jews to convert or leave Spain, was actually the conclusion of a century-long process. The Marranos’ ordeal began in 1391, when a popular preacher named Ferran Martinez instigated a massive pogrom in Seville. About four thousand Jews were killed in that city alone, and the attacks soon spread. One witness described how, in Barcelona, a Christian mob used catapults to attack the towerwhere Jews had taken refuge: Some slew themselves, others jumped from the tower where Jews had taken refuge: “Some slew themselves, others jumped from the tower . . . and all the rest converted.”Such mass conversions, repeated across the country and augmented by similar pogroms in later years, created a new class in Spain: the New Christians, disparagingly called Conversos or Marranos. (This last name is sometimes avoided by Jews who remember that it was a term of contempt, but Yovel considers it “a neutral scholarly term.”) With great subtlety and penetration, Yovel shows how the New Christians posed a major theological and social challenge to Catholic Spain. The Jews, along with the Muslim Moors, had long been the “Other” against which an increasingly militant Spanish Catholic identity defined itself. Now that they were themselves Catholics, however, the Marranos became an “Other Within”: nominally part of the nation, they in fact remained socially, economically, and religiously distinctive. Indeed, the Portuguese Marranos—Jews who fled Spain for Portugal in 1492, then found themselves prey to the same coercion there—began to refer to themselves as “the Hebrew Nation” or just “the Nation.” They were ethnically, and as Yovel says “existentially,” Jewish, even as they gradually lost touch with the actual content of rabbinic Judaism.It was to confront this existential threat that Spain introduced the first blood purity laws, which defined Jewishness as a genetic taint, much like the Nazi race laws five centuries later. As Yovel notes, this kind of discrimination between Old Christians and New Christians went directly counter to traditional Catholic dogma. But then so did the institution of the Inquisition, which was created in 1480 as an arm of the Spanish state, not of the Papacy. While recounting all the horrors of the Inquisition—the informers, the perversion of legal process, the tortures, the burnings—Yovel notes that Jews themselves were completely immune to them. Jews were never under the jurisdiction of the Inquisition, because they were never part of the Church (though they were very much vulnerable to popular hatred and pogroms, and were eventually forced to flee the country altogether). It was only the conversos, who converted specifically to avoid persecution, who could be persecuted for backsliding or “Judaizing.” And this sin was very loosely construed: eating traditional Jewish dishes, or even changing your shirt on Saturday, was considered a dangerous sign by the inquisitors.The most fascinating parts of The Other Within are devoted to the distinctive culture that the Marranos evolved under these trying conditions. Yovel introduces the reader to a number of distinguished Marranos: Juan Luis Vives, the Spanish Renaissance polymath; Teresa of Avila, the mystical psychologist; Baruch Spinoza, the first philosopher of atheism; and even the essayist Michel de Montaigne (his mother’s family were conversos named Lopez). It is tempting to see these great questing minds as distinctively Marrano—in their distrust of conventional religion, their empiricism and skepticism, their yearning to explore what Teresa called “the interior castle” of the self. Belonging neither to Judaism nor to Christianity, such men and women had to create a new mental world, which we can now recognize as characteristically modern.Yet is it really possible, or even meaningful, to say that modernity itself, or such primal things as conscience and selfhood, were invented in the 16th century by the descendants of Iberian Jews? Are the Marrano origins of modernism a historical fact or Yovel’s ingenious metaphor? He himself seems unsure: “Although direct linear causes must have been at work,” he writes, “they are hard to isolate and even harder to measure.”In fact, many of the phenomena Yovel considers essentially Marrano can be discovered earlier than 1391, and in parts of the world where Spanish Jews never set foot. Urban culture was already flourishing in northern Italy in Dante’s time; the great exponent of scientific rationalism was Francis Bacon, an English Protestant; and as for religious heterodoxy, the Marranos had nothing on Martin Luther, not to mention Jan Hus or John Wycliffe. What Yovel sees as Marrano, in other words, is the whole complex of social changes that are conventionally referred to as the Reformation and the Renaissance: a continental, civilizational shift that cannot plausibly be attributed to the experience of a few hundred thousand Marranos. It is far more convincing to say that Marranism was one manifestation of that shift—a peculiar and extreme one, thanks to the exceptional circumstances in which the New Christians were forced to live. As The Other Within shows, the Marrano experience remains one of the most provocative chapters of Jewish and European history—if not, finally, the most important one.Adam Kirsch is a poet and literary critic, whose books include The People and the Books: 18 Classics of Jewish Literature.