Introduction

      Sefer Yeṣirah is one of the most enigmatic, yet influential, texts in the history of Jewish thought. The text is striking for its rhythmic phrasing and evocative language; it connects the essence of language with the foundations of the world. This short treatise has fascinated Jewish thinkers and kabbalists, as well as Western thinkers and writers, from Gottfried Wilhelm Leibniz to Umberto Eco and Jorge Luis Borges.

      Because of its unique style as well as the fact that it does not explicitly refer to other Jewish sources and was not quoted by other Jewish sources in late antiquity, it is difficult, if not impossible, to contextualize. When I present Sefer Yeṣirah for the first time to my students, I joke that after about 150 years of scholarship on Sefer Yeṣirah, we know almost everything about this book except for four minor issues: Who wrote it? Where and when was it written? What does it mean? And what was its “original” version? Scholars disagree about the time and context of the book, proposing first-century CE Hellenism,¹ the rabbinic sphere of the second to sixth centuries CE,² Neoplatonism of the fourth or fifth centuries CE,³ fifth to the sixth century CE Palestine,⁴ the Syriac-Christian milieu of the sixth to seventh century,⁵ or the ninth-century Islamic world.⁶ This diversity reflects what seems to be an inherent and radical inability to contextualize Sefer Yeṣirah.

      Sefer Yeṣirah appeared in the Jewish world at the beginning of the tenth century. In this period, it was already interpreted as a canonical treatise by leading rabbinic figures living on three continents, and it had many different versions. The surprising appearance of Sefer Yeṣirah, as if out of the blue, is the result of its absence from the Jewish world before the tenth century, along with its immediate acceptance. Furthermore, Sefer Yeṣirah had a remarkable reception in Jewish milieus from the tenth century on. Joseph Dan describes the two main stages of its impact on the Jewish world—stages with little in common:⁷ in the first, between the tenth and the twelfth centuries, it was read by at least five commentators as a sort of philosophical or scientific text.⁸ In the second, from the end of the twelfth century on, it was interpreted by mystics and kabbalists as a mystical, mythical, and magical treatise. These facts about Sefer Yeṣirah’s reception raise essential questions: Where was Sefer Yeṣirah before its canonization in the tenth-century rabbinic world? Why was Sefer Yeṣirah initially understood as a philosophical and scientific treatise, and later viewed