Against a decidedly mixed background of prosperity and adversity, Jews in the Crown of Aragon enjoyed a brilliant and vigorous intellectual life throughout the fourteenth century—and the wealthiest and most cosmopolitan part of the Crown was Catalonia, in particular the royal seat of Perpignan. There, Jews excelled in the practice of medicine and composed works of philosophy, literature, exegesis, and more. The Jewish “intellectual effervescence”¹ of this period was open to many different traditions and strains, with Arabic-influenced philosophical rationalism thriving alongside kabbalah and the Talmudic scholarship of northern France. Other strong elements in the elite culture of rationalist...

Born most likely in the mid-to late 1350s, Profayt Duran belonged to a relatively well-off family that had been settled in Perpignan, a city at the northernmost tip of Catalonia, for at least a generation.¹ In absolute numbers, the Perpignan Jewish community was not impressive: hearth-tax rolls indicate between one hundred and three hundred families out of a total population of approximately eighteen thousand over the course of the fourteenth century, a size far below that of the Jewish community either in Barcelona or in Narbonne in southern France.² But despite its small numbers, the Perpignan community flourished.

Under King...

As was the case in general for the Iberian Jewish elite, Duran’s education included basic scientific knowledge. But scientific activity, in particular astronomy, was also unusually central to Duran’s thought and made up a large proportion of his writings. He taught mathematics and astronomy at a practical level, studied more advanced texts, and corresponded on astronomical and numerological issues with his peers.

Histories of early modern science in the Iberian Peninsula depict a rich legacy of empirical, experimental, and practical activity.¹ The imperatives of Spanish and Portuguese overseas commerce and empire building encouraged such fields as cartography and navigational instrumentation.²...

In the seventeenth century, Joseph Solomon Delmedigo (1591–1655) reported in a letter that while in Egypt he had seen something like eighteen commentaries on theGuide, long and short. He classified four of them by reference to the four sons of the Passover haggadah. One was by “Efodi,” a variation of the name Efod that was used to refer to Duran beginning sometime in the fifteenth century. Delmedigo’s evaluation of Duran as the son “who does not ask” sounds at first negative. But in fact Delmedigo is not pleased with radical commentators, like Moses Narboni, who inquire too deeply...

In the thirteenth century, Aristotelian Jewish philosophy had been at a peak. The translation into Hebrew of, among many other works, ibn Rushd’s commentaries on Aristotle and the immensely influentialGuide of the Perplexedled to what has been called “the consolidation of Spanish rationalism under the banner of Maimonides.”¹ By the end of the century, Aristotelianism was dominant among the majority of philosophically inclined writers, and in many cases was considered identical with philosophy itself. Kabbalists, too, like Isaac ibn Latif (c.1210–1280) and Abraham Abulafia (1240–c.1291), were influenced by Aristotelian ideas.²

A hundred years later, however—which...

Science, even in its weak medieval sense of “natural philosophy,” is usually thought of as unrelated to particular religious beliefs. And to some extent, the knowledge of the natural world sought by medieval scholars was indeed held by them to be “true” in a universal sense. God’s creation was the same for all, and the tools of logic and mathematics used to understand that creation were a matter of common agreement, even among scholars of widely differing religious and philosophical orientations.

This nonsectarian quality may also be said to characterize the basic mathematical techniques, practical methods of astronomical calculation from...

I begin with a quick sketch of the background to Duran’s view of astronomy.

As an attempt to apprehend the particulars of the heavens, to understand their motions, and to find mathematical models that predict and explain those motions, astronomy was associated in the Middle Ages with mathematics, a field of endeavor often considered to possess a unique epistemological status and a superior claim to truth.

To quote Gersonides, here following a long tradition beginning with Aristotle, “no mistake can befall concerning the truth produced by [the mathematical sciences] through mathematical demonstrations.”¹ From its close dependence on mathematics, astronomy, too,...

Mathematics, absolutely fundamental to theoretical astronomy, would appear to be the most universal of all the sciences. If its appeal for Duran may have stemmed in part from a practical interest in its usefulness, he also saw it as the human intellect’s most reliable tool for understanding the world, and, as I have argued, the only possible route to learning about the celestial realms and attaining the glimmer of knowledge about God those realms might provide. There was yet another aspect at work as well. It lay in the area of neo-Pythagorean speculation sometimes called arithmology: the “branch” of mathematics...

In 1395, Duran composed a brief treatise on the Jewish calendar titledḤeshev ha-Efod(“Cincture of the Efod”).¹ At first glance, its purpose would appear obvious and immediate. In the turmoil of the early 1390 s in Catalonia, the Jewish communities, with many of their number dead or lost to Judaism, were faced with the need to fulfill a basic requirement of communal religious life: namely, setting the dates of the holidays and fasts of the coming religious year.

It is unclear to whom this task would have fallen even in ordinary times. Certain authorities must have issuedluḤot,tables...

Al tehi ka-avotekha(“Be Not Like Your Fathers”) was composed approximately three years after Duran’s conversion.¹ It takes the form of a satirical epistle to another recent New Christian, one David Bonet Bonjorn, who had converted out of a professedly sincere desire to embrace Christianity.

The “traditional” interpretation of this letter is that it was written by one forced convert (Profayt Duran) to another (Bonjorn) who had begun to look favorably on his new faith.² Yet there is no reference to forcible conversion in the text; Duran cites only a letter in which Bonjorn has expressed his new convictions, and...

InAl tehi ka-avotekha, the subject of the previous chapter, satirical form camouflages the sharpness of the criticisms of Christianity.Kelimat ha-goyim, a somewhat later work, is a direct attack on contemporary Christian dogma.¹ As inAl tehi ka-avotekha, Duran’s underlying assumption is that reason is an irrefutable source of truth and that arguments based on it have the most power to convince. Here, however, he takes a far more analytical approach, combining an awareness of the historical development of religion with a striking mastery of Christian texts and doctrine.

Duran begins with a dedication to an unnamed sage who,...

In 1393, Duran composed a eulogy for Abraham ben Isaac ha-Levi of Girona, a gifted poet and rabbinic leader of his people.¹ Addressed to En Joseph Abram, the son of the deceased, the eulogy may have been intended to be read aloud at a memorial service or otherwise circulated among the mourners. Reflecting some of the agonies endured by the Jewish communities of Catalonia, the eulogy offers a kind of laboratory setting in which to observe the playing out of such issues as the causes of Jewish suffering, faith in God and rebellion against God, the definition of a Jew...

Ma‘aseh Efodis by far the most important of Duran’s writings, and it represents the clearest expression we have of his vision and beliefs.¹

In this apparently innocuous work of Hebrew grammar, with its unusually substantial introduction, Duran encodes a double message. A man who in cold reality is living as a Christian, he appears intent on presenting himself as a moderate, traditional, thoroughly Jewish guide to his chosen subject. His philosophical language is normative, his cited references are nearly exclusively to Jewish sources, and his “we” is the we of the Jewish community. Whereas mostconversoliterature is written...

InMa‘aseh Efod,as we shall presently see, Duran draws from Maimonides’Guide of the Perplexedwhile also disclosing an unusual awareness of contemporary magical practices. This combination—of select Maimonidean texts with the medical-magical concept of occult virtue (segulah)—makes for a system of religious experience that, while couched in highly conventional philosophical language, also marks a striking departure from the Maimonidean intellectualist tradition. The transmutation was carried out, in my view, under the pressures of Duran’sconversoexistence and—to all appearances—in its service. Theconversos’ former relationship with normative Jewish practice has been irrevocably shattered. In...