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Averroism in Iberia: Yitzhak Baer, Álvaro Pelayo and Questions about Jewishness

Thomas Hendrik Kaal, Queen Mary University of London

Zusammenfassung: Die erzwungene Konversionsbewegung von iberischen Juden im Jahr 1391 wirft nach wie vor viele Fragen auf. Warum konnten so viele Sephardim dazu gebracht werden, ihrem ererbten Glauben zu entsagen und Christen zu werden? Für Yitzhak Baer lag der Schlüssel zu dieser Frage in der Verbreitung des sogenannten Averroismus. Seine Ansicht nach hatte rationalistische Philosophie die religiösen Überzeugungen derart unterminiert, dass insbesondere die gebildeten Juden nicht mehr bereit waren, Vertreibung oder den Märtyrertod zu erdulden. Baers Hypothese ist bereits aus unterschiedlichen Perspektiven kritisiert wurden. Dieser Artikel eröffnet eine neue Sichtweise auf die Thematik, in dem er den Blick auf Averroismus in christlichen Quellen richtet. Den Ausgangspunkt der Überlegungen bildet das häresiologische Kompendium Collyrium fidei des Franziskaners Álvaro Pelayo.

Abstract: The forced mass conversion of Iberian Jews in 1391 continues to raise numerous questions. Why could so many Sephardim be brought to renounce their inherited faith and become Christians? Yitzhak Baer believed that the key to answering this question lay in the spread of Averroistic philosophy among the Sephardim. In his view, rationalist philosophy had so deeply undermined the religious faith of many Iberian Jews, particularly of the more educated, that they were no longer willing to endure expulsion or martyrdom. Baer’s interpretation of Averroism has been criticized from various perspectives. This article proposes a new approach to the subject, shifting the focus to the representation of Averroism in Christian sources, with the heresiological compendium Collyrium fidei by Franciscan friar Álvaro Pelayo serving as a starting point for further reflections.

In his famous study History of the Jews in Christian Spain, the German-Israeli historian Yitzhak Baer (1888–1980) suggested that Spanish Jewry in the Late Middle Ages was deeply influenced by a philosophical current known as “Averroism”.1 This tradition, named after Ibn Rushd (1126–1198), is said to be most notably characterized by the belief that religion and philosophy are entirely separate, enabling them to arrive at different conclusions without contradicting or undermining one another.2 Baer argued that this split between the realm of knowledge and the realm of faith weakened the Jewish community in Iberia, making them more vulnerable to conversionary pressure. For if one could no longer determine beyond reasonable doubt that Judaism was true, and Christianity false, then there was significantly less incentive for a Jew to remain faithful to his or her inherited religion. When many Jews at the end of the 14th century were confronted with the choice of either converting to Christianity or dying the death of a Jewish martyr, those affected by Averroism simply could not muster the strength to remain faithful to their religion but converted to Christianity in large numbers. Baer thus argued that Averroism was the key factor behind the mass conversions of Jews in Spain in 1391.3 Based on his thesis, Averroism has become a recurring theme in the academic debate about the converts and their numerous descendants, the so-called conversos. It is used to explain the deviant religiosity, unbelief and skepticism among the New Christians, which can be found in 15th-century sources, especially in inquisition records.4

Scholars have long criticized Baer’s thesis for lacking sufficient evidence.5 A Jewish convert who explicitly invoked Averroism as a justification for the pragmatic acceptance of Christianity has yet to be identified. While Baer cited the works of Jewish anti-philosophers to support his claims, Daniel J. Lasker demonstrated decades ago that the tenets of Averroism did not prevent authors from maintaining their belief in the rational superiority of Judaism. It was entirely possible to be both “an Averroistic philosopher and a loyal Jew”.6 So, considering the inner Jewish debate, the evidence for Baer’s thesis appears rather thin. But what about Christian sources? Baer suggested that Christian guardians of orthodoxy feared a rationalist undermining of their faith through the corrosive influence of Averroism in the guise of Jewish converts. The persecution of conversos by the Spanish Inquisition, therefore, appears to be a response to the realization that many of them were but “philosophical intellectuals, Averroists, and nihilists”.7 This raises the possibility of finding indications of the spread of Jewish Averroism in contemporary Christian sources. Yet, the representation of Jewish Averroism in Christian sources from the Iberian Peninsula has not yet been studied in depth. This article is part of an ongoing research project, offering a few initial observations drawn from a heresiological compendium titled Collyrium fidei by friar Álvaro Pelayo (1280–1350).

Collyrium fidei is a peculiar text. It shows Álvaro Pelayo as a particularly unforbearing persecutor of religious deviance.8 In Book V, Álvaro condemns the heresy of a certain Thomas Scotus, an intellectual Averroist par excellence: Thomas reportedly argued that the world should be governed by philosophy rather than religious laws. He held that Judaism, Islam, and Christianity were sinister machinations of three impostors—Moses, Jesus, and Mohammed. He rejected the virgin birth, did not believe in angels, demons, the sacraments, creation ex nihilo, or any notion of an afterlife. Thomas also thought that all miracles were either false or could be fully explained by natural processes.9 To modern readers, this may sound like the description of a skeptical, ‘enlightened’ intellectual. But this was not how Álvaro understood the position of his opponent. Rather, he was visibly concerned to connect Thomas’ Averroistic position with Judaism. The friar went to great lengths to argue that Thomas was, in fact, a Judaizer.

What can Collyrium fidei tell us about the perception of Averroism in late medieval Iberia? First, we learn that zealous friars like Álvaro Pelayo were definitely concerned about the detrimental impact of Averroistic philosophy. Secondly, Collyrium fidei evidences a strong discursive connection between Averroism and Judaism. However, it seems that this connection existed more in Álvaro’s mind than in reality. For the friar, any form of unbelief and questioning of Christian truth claims was automatically akin to Judaism. Judaism functioned as a hermeneutical lens through which Christian authors could recognize and condemn unwanted tendencies in society and even in their own thinking.10 Considering that Collyrium fidei was already written decades before the mass conversion of 1391, we can see it did not take a mass influx of Averroistic conversions, as envisaged by Baer, to establish a closeness between heterodox Aristotelianism and Judaizing in Christian Iberian heresiology. The idea that Spanish Inquisitors in the late 15th century out of the blue ‘discovered’ a connection between Judaizing conversos and Averroism is clearly mistaken. This observation calls us to further investigate the discursive identification of heterodox philosophical ideas with Judaism in contemporary Christian discourses, especially with regards to the so-called converso problem—the growing concern about the New Christian population in Iberia that ultimately led to the Spanish Inquisition. In doing so, one discovers that some of the essentialist notions of Jewishness evident in medieval sources continue to shape the scholarly debate on conversos, in Yitzhak Baer’s time as well as today.


Photo: Andrea di Bonaiuto, Triumph of St. Thomas and Allegory of the Sciences, 1365–1368, fresco, Cappella Spagnuola, Santa Maria Novella, Florence, in; Wikimedia Commons, URL: [https://creativecommons.org/licenses/by/3.0] (20.08.2024).

  1. Yitzhak Baer, A History of the Jews in Christian Spain (Philadelphia: Jewish Publication Society of America, 1961), I, 240, 263, 290 and II, 52, 137–138, 253–259. []
  2. This distinction is usually inferred from Averroes’ Kitab Fasl al-Maqal. On his attempt to reconcile the claims of reason with the demands of faith, see Diego R. Sarrió, ‘The Philosopher as the Heir of the Prophets. Averroes’s Islamic Rationalism’, Al-Qanṭara, 36 (2015), 45–68. []
  3. Baer, A History of the Jews, 138: “Apart from material considerations, it was the Averroist outlook that in the main prompted the better educated Jews to choose the easiest way. […] Those individuals who habitually looked down upon the simple masses who scrupulously observed all the commandments, these same men, when the test came, lacked the spiritual fortitude to prefer death to apostasy. In much the same spirit as they had previously denied the authority of biblical law, they now accepted the rites and ceremonies of an alien religion; ultimately, they only remained faithful to their ‘religion of the intellect’.” []
  4. See, among others, See Francisco Márquez Villanueva, ‘El caso del averroísmo popular español (hacia la Celestina)’, in José Luis Canet Vallés and Rafael Beltrán Llavador (eds.), Cinco siglos de “Celestina”. Aportaciones interpretativas (Valencia, 1997) and Yirmiyahu Yovel, The Other Within: The Marranos: Split Identity and Emerging Modernity (Princeton: Princeton University Press, 2009), 44–5. []
  5. See, for example, Norman Roth, Conversos, Inquisition, and the Expulsion of the Jews from Spain (Madison: University of Wisconsin Press, 1995), 61–5. []
  6. Daniel J. Lasker, ‘Averroistic Trends in Jewish-Christian Polemics in the Late Middle Ages’, Speculum, 55 (1980), 304. []
  7. Baer, A History of the Jews, II, 224, 274. []
  8. Álvaro Pelayo, Collyrium fidei, ed. and trans. by Miguel Pinto de Meneses, Lisbon 1954–1956. []
  9. For a summary of the accusations against Thomas see Michele de Araújo, Tradição e poder no colírio da fé: um estudo sobre heresiologia política medieval (Brasilia: University of Brasilia, 2015), 69–70. []
  10. David Nirenberg, ‘Enmity and Assimilation’, Common Knowledge, 9 (2003), 151. []

Converso Unbelief in Fortalitium Fidei by Friar Alonso de Espina

Thomas Hendrik Kaal, Queen Mary University London

Zusammenfassung: In seinem Werk Fortalitium Fidei (c. 1464) entwirft der Franziskanermönch Alonso de Espina eine neue Konzeption der Häresie des Judaisierens. Anstatt Judaisieren lediglich als klandestine Fortführung jüdischer Glaubensvorstellungen und Praktiken zu verstehen, sah er darin eine noch schlimmere häretische Verirrung. Den judaisierenden conversos warf er vor, jedwede religiöse Tradition aufgegeben zu haben und der zuerst von Epikur vertretenen Überzeugung zu folgen, dass die menschliche Seele mit dem Tod erlösche. Dieser von Espina propagierte Diskurs bereitete den Weg für die Verknüpfung zwischen den Neuen Christen und der Leugnung der Unsterblichkeit, die sich später in den Akten der Spanischen Inquisition gegen Ende des 15. Jahrhunderts nachweisen lässt.

Abstract: In his Fortalitium Fidei (c. 1464), the Franciscan friar Alonso de Espina outlines a new conception of the Judaizing heresy. Instead of seeing Judaizing merely as a clandestine continuation of Jewish beliefs and practices, he saw it as an even worse heretical aberration. He argued that most conversos had abandoned all religious traditions, sharing the conviction, first held by Epicurus, that the human soul expires after death. Espina’s discourse paved the way for the link between the New Christians and the denial of immortality, which can be observed in the files of the Spanish Inquisition produced at the end of the 15th century.

The trial records of the Spanish Inquisition feature an astonishing number of people who were accused of not believing in the immortality of the soul.1 The majority of these individuals were conversos, that is to say Iberian Jews who had been forcibly converted to Christianity in the course of the 15th century, as well as their numerous descendants. Brought before the tribunals on suspicion of Judaizing, these conversos seem to have disregarded both the Christian and the Judaic religion.2 Instead of following either of the two laws, they were said to act on the maxim that there was nothing to human life except being born and dying (nada que nascer e morir). Scholars have tended to interpret such testimonies as evidence of a secret current of religious skepticism among the New Christians, sometimes called ‘popular Averroism’.3 The alleged disbelief in immortality is seen as a precursor of subsequent religion-skeptical tendencies among the descendants of Iberian Jews, culminating in the skeptical philosophy of 16-century Marranos such as Uriel da Costa and Baruch de Spinoza.4

This article forms part of an ongoing research project that re-examines the relationship between conversos and religious skepticism in 15th century Castile. It aims to show that disbelief in immortality formed part of a stereotypical view of the New Christians, which emerged decades before the first inquisitorial tribunal began its work in Castile.5

One of the first contemporary authors to associate conversos with disbelief in immortality was the Franciscan friar Alonso de Espina (c.1410–1465). His magnum opus bears the programmatic title Fortalitium Fidei contra iudeos, saracenos aliosque christiane fidei inimicos (“The Fortress of Faith against Jews, Saracens and all other Enemies of the Christian Faith”).6 The text was one of the most ambitious heresiological treatises written in the late Middle Ages. It exposes what the Franciscan perceived as the war of Christianity against its various enemies: Jews, Muslims, heretics, and demonic forces, each of which are dealt with separately in one of five books. Espina paints the bleak picture of a society under siege: as depicted in the above illustration, Jews would attack the fortress of faith with their blind rejection of the gospel, Muslims would threaten the Christian kingdoms with war and demons wreak havoc like never before; but worst of all, the foundations of the faith were about to be completely undermined by heretics. Here, Espina pointed to the conversos as the main threat to religious orthodoxy. He argued that the majority of New Christians had succumbed to a particularly wicked heretical deviation, which would even exceed the blind unbelief of the Jews.7

For Alonso de Espina, the Judaizing heresy of the conversos was far worse than a simple relapse to Jewish customs. He conceptualized it as a deliberate denial of all religious traditions. Rendering the results of an alleged Toledan inquiry, the friar claimed that many New Christians had abandoned both the Jewish and the Christian law. They would consider the teachings of the church to be a massive swindle (truffa) and disregard both the Old and New Testament as silly fairytales, written to mislead the simpleminded. Instead of following any of the established religious traditions, the New Christians would deny the afterlife and live only for material pleasure and success. To summarize their wicked irreligiosity, Espina stated that the conversos believed in nothing but “being born and dying”—the very formulation that later featured in the trial records of the Spanish Inquisition.8 The friar warned that mortalist ideas as believed by the New Christians could easily spread to other parts of society. He admitted that even the most pious believer might occasionally wonder whether the Christian claims about the afterlife were actually true. Since the devil would constantly try to dissuade people from the true faith, the presence of heretics who denied immortality posed an immediate threat to the inner stability of a Christian society. The spread of mortalist ideas thus had to be stopped at all costs. Espina argued vehemently that the only way was to establish a general inquisition in Castile, which should put an end to the Judaizing heresy.9

Fortalitium Fidei had a considerable impact on the debate about the New Christians in the last decades of the 15thcentury. Following the argument set out by Alonso de Espina, disbelief in immortality emerged as a distinctive feature of crypto-Judaism. Scholars like Ana Echevarría have argued that Fortalitium Fidei served as an important handbook for the early Spanish Inquisition.10 This would explain why many first-generation inquisitors categorized disbelief in immortality as tantamount to Judaizing. Rather than evidencing an averroistic current among the conversos, the plethora of mortalist statements recorded by inquisitors thus seems to point to the cultural hinterland that gave rise to the inquisition in the first place. The testimonies demonstrate that in the context of inter-religious conversion, radical unbelief served as a particularly effective accusation to vilify any form of religious deviance.


Photo: Alfonso de Espina, Fortalitium Fidei, Basel 1475, in: ourheritage.ac.nz, URL: [https://otago.ourheritage.ac.nz/items/show/6330] (01.02.2023).

  1. See for example the evidence from Soria, El Tribunal de la Inquisición en el Obispado de Soria (1486–1502), Carlos CARRETE PARRONDO (ed.), (Fontes Iudaeorum Regni Castellae, 7), 1985, Salamanca. The records have been anaylized by MONSALVO ANTON, José M. 1984: »Herejia conversa y contestacion religiosa a fines de la Edad Media. Las denuncias a la Inquisicion en el obispado de Osma«, Studia historica: historia medieval, Vol. 2, pp. 109–138 and EDWARDS, John 1988: »Religious Faith and Doubt in Late Medieval Spain. Soria circa 1450–1500«, Past & Present, Vol. 120, pp. 3–25. []
  2. See PASTORE, Stefania 2016: »Doubt in Fifteenth-Century Iberia«, in GARCÍA-ARENAL, Mercedes (ed.), After Conversion. Iberia and the Emergence of Modernity, Leiden, pp. 283–303. []
  3. MÁRQUEZ VILLANUEVA, Francisco 1994: »Nasçer e morir como bestias (criptojudaísmo y criptoaverroísmo)«, in DÍAZ ESTEBAN, Fernando (ed.), Los judaízantes en Europa y la literatura castellana del siglo de oro, Madrid, pp. 273–293. []
  4. This interpretation has been spearheaded by NIEWÖHNER, Friedrich 1988: Veritas sive varietas. Lessings Toleranzparabel und das Buch Von den drei Betrügern, (Bibliothek der Aufklärung, 5), Heidelberg and YOVEL, Yirmiyahu 2009: The Other Within. The Marranos: Split Identity and Emerging Modernity, Princeton. []
  5. The project ties in with the methodology of WELTECKE, Dorothea 2010: “Der Narr spricht: Es ist kein Gott”. Atheismus, Unglauben und Glaubenszweifel vom 12. Jahrhundert bis zur Neuzeit, (Campus historische Studien, 57), Frankfurt am Main. []
  6. The earliest Latin manuscript, preserved in the Archive of the Burgo de Osma Cathedral, dates back to 1464 (Codex No. 154). All quotations in this article are from the 1487 incunabulum of the work printed in Lyon. []
  7. On Jews and heretics in Fortalitium Fidei see CAVALLERO, Constanza 2016: Los enemigos del fin del mundo. Judíos, herejes y demonios en el Fortalitium Fidei de Alonso de Espina (Castilla, siglo XV), Buenos Aires. and VIDAL DOVAL, Rosa 2015: Misera Hispania. Jews and Conversos in Alonso de Espina’s Fortalitium Fidei, (Medium aevum monographs, 31). []
  8. “Sexta, quod fides catholica erat quedam truffa et quod nihil aliud erat in hac vita nisi nasci et mori et quod totum aliud vanitas erat”, Alonso de Espina, Fortalitium Fidei, II, 6, 1, f. 53 v.a. []
  9. “et specialiter iuxta posse suum laborat quod faciat eum dubitare quod sit altera vita nisi hec, et quod debeat fieri resurrectio mortuorum, quia si hoc facit eum credere vel in hoc dubitare, statim homo sic deceptus dimittit se cadere in omnem peccatum, et elongatur ab omni virtute, et perdit omnem timorem et amorem Dei, et vivit desperatus qui perdidit totam fidem et spem Dei”, Alonso de Espina, Fortalitium Fidei, II, 6, 13, f. 63 v.a. []
  10. Echevaria, Ana 2022: »The Perception of the Religious Other in Alonso de Espina’s Fortalitium Fidei: A Tool for Inquisitors?«, in Constable, Olivia Remie (ed.), Interfaith relationships and perceptions of the other in the medieval Mediterranean. Essays in memory of Olivia Remie Constable(Mediterranean perspectives), Basingstoke, pp. 161–195. []