Abraham bar Chiya

• Philosophy and Theology
• Contribution to Mathematics and Science
• Eschatology and Calculating the End
• Innovations in the Hebrew Language
• The Science of Intercalation and Astronomy
• The Scientific Work and the Torah-Philosophical Teaching of Rabbi Abraham bar Chiya ha-Nasi
• Biographical Background, Political Standing and Bar Chiya's Role as Mediator

Rabbi Abraham bar Chiya ha-Nasi (known in Latin scientific sources as Savasorda) is counted among the most influential and versatile figures to emerge from Spanish Jewry in the period of transition between the Golden Age and the beginning of the later Middle Ages ^{[cite: 1, 2, 3]}. He was active at the end of the 11th century and in the first half of the 12th century in Barcelona in Christian Spain, and also in Narbonne in France ^{[cite: 3, 4, 5]}. Historical estimates indicate that he was born between 1065 and 1070 and died around 1136, although some evidence points to his joint scientific activity with the Latin translator Plato of Tivoli until 1145 ^{[cite: 2, 3, 5]}.

Bar Chiya's public and social standing was exceptional both within the Jewish community and in the Christian and Muslim royal courts. The Hebrew title attached to his name, "ha-Nasi" (the Prince), is attributed by scholars to his family's belonging to royal seed and Davidic lineage, apparently descendants of Hezekiah, Exilarch of Babylonia, who migrated to the Iberian Peninsula ^{[cite: 5, 6]}. On the other hand, his Arabic title "sahib al-shurta" (صاحب الشرطة), corrupted in Latin into the appellation "Savasorda," testifies to his holding a high-ranking government office at the royal court of Barcelona and in the service of Alfonso I, King of Aragon ^{[cite: 1, 3, 5]}. This office, whose original meaning is "commander of the guard" or chief of police, developed in the Spanish principalities into the role of a senior adviser and royal land surveyor, combining scientific knowledge with broad judicial and administrative powers ^{[cite: 3]}.

Bar Chiya acquired his broad scientific and philosophical education in the city of Saragossa in the time of the Muslim Banu Hud dynasty, where he gained complete mastery of the Arabic and Greek sciences ^{[cite: 3]}. As one who lived on the border between the Muslim and Christian worlds, he developed the historical role of a cultural mediator, and was the first to transmit the treasures of scientific and philosophical knowledge written in Arabic to the Jewish-Christian world of Barcelona and Provence, translating and composing original books in the Hebrew language ^{[cite: 3, 5]}.

To understand the scope of his scientific and intellectual work, the following table presents the whole of his known works, their estimated years of composition and the extent of their historical dissemination:

His Philosophical and Theological Teaching

The philosophical and theological teaching of Rabbi Abraham bar Chiya is founded on an original fusion of Neoplatonic and Aristotelian conceptions with the traditions of the Bible and the Talmud ^{[cite: 3, 7]}. He held the principled position that all branches of the sciences and of wisdom originally belonged to the people of Israel, and that the nations of the world learned them from Israel in ancient times, a fact that justifies returning them to the bosom of the Hebrew language ^{[cite: 3]}.

Cosmogony, Metaphysics and the Doctrine of Emanation

Creation, according to Bar Chiya, took place out of absolute nothingness (ex nihilo), the act of creation being expressed in the appearance of all the forms as a divine potential in the thought of the Creator ^{[cite: 3, 7]}. The stages of creation described in the Book of Genesis are nothing but the gradual passage of those forms from potentiality to actuality ^{[cite: 3]}. In this process, matter and form play opposed and complementary metaphysical roles: matter is divided into pure matter and turbid matter, called "the dregs of matter," while form is divided into closed form and open form ^{[cite: 3, 7]}.

From the most closed and purest form, which is incapable of merging with matter, emanated the supernal light of the first day, which makes up the eternal upper world, the world of the angels and the souls ^{[cite: 3, 7]}. The radiant light acts upon the open form, granting it the capacity to join with matter ^{[cite: 3, 7]}. This union of form and matter produces the fixed heavenly bodies (when the form joins with pure matter) and the corporeal and transient entities of the sublunar world (when it joins with the metaphysical dregs of matter) ^{[cite: 3, 7]}.

The Definition of Time and the Limits of Reality

Understanding the concept of time in Bar Chiya's teaching is a critical layer for understanding both his cosmological and his eschatological position. In his book "Megillat ha-Megalleh" (The Scroll of the Revealer) he opens with a profound philosophical discussion of the nature of time ^{[cite: 2]}. In his view, time is a category dependent on existing things and does not exist in itself but only within the intellect, and it is "seen by the eyes of the heart" ^{[cite: 2]}. Existence within time means limitation and measurement between past and future, and therefore the eternal and divine entities are not within time but beyond it ^{[cite: 2]}.

The cosmic system is governed by means of two emanated hypostases: the Intellect, which holds all the forms in a fixed and eternal state without change, and the Soul, which holds the forms in perpetual motion that is the source of life and motion in the corporeal world ^{[cite: 2]}. Julius Guttmann pointed out that Bar Chiya's definition of time harbors many internal contradictions, since he attempts to hold at one and the same time an objective Aristotelian conception of time dependent on physical motion, together with a subjective and idealist conception of time existing in human consciousness alone ^{[cite: 2]}. This concept of time is closely bound up with his concepts of causality; as Rabbi Levi ben Gershom (Ralbag) noted, Bar Chiya developed a distinctive definition of "priority in cause," in which the prior factor is the direct cause of the existence of what comes after it ^{[cite: 14]}.

Psychology, Free Will, and the Doctrine of Morality and Repentance

Bar Chiya's doctrine of the soul and of the moral qualities is set out at length in his principal philosophical book, "Hegyon ha-Nefesh ha-Atzuvah" (Meditation of the Sad Soul) ^{[cite: 4, 12]}. The work, which draws inspiration from the spirit of morality and asceticism of the literature of Muslim Spain, such as "Chovot ha-Levavot" (Duties of the Heart) by Rabbenu Bachya ibn Paquda, deals with human psychology and the metaphysical foundations of morality ^{[cite: 3, 4, 12]}. Bar Chiya adopts the threefold division of the powers of the soul: the vegetative soul, the animal soul and the speaking soul, and demands the absolute rule of the rational, speaking soul over the bodily lusts and drives ^{[cite: 3, 7]}.

Nevertheless, his central innovation lies in the separation he makes between the intellect and the will ^{[cite: 12]}. In his view, man's free choice does not flow automatically from the intellect but from the independent will ^{[cite: 12]}. The process of moral rectification requires a conscious decision to develop the intellect so that it will be able to distinguish between good and evil, and thereafter a free act of will is required to apply the insights of the intellect and to flee the vanities of this world ^{[cite: 12]}. He sees suffering and evil in the world as a divine instrument intended to test the righteous and to punish the wicked, and he preaches moderate asceticism as a way of purifying the soul ^{[cite: 3, 7]}. The inner structure of the book "Hegyon ha-Nefesh ha-Atzuvah" reflects this moral progression, and it is divided into four principal gates, as detailed in the following table:

The Four Fates of the Soul and the Controversy over Transmigration

The fate of the soul after death is closely bound up with the level of wisdom (the health of the soul) and righteousness (the vitality of the soul) that it attained during its life ^{[cite: 3]}. The upper world is divided into five levels of light, to which the souls ascend according to their spiritual state ^{[cite: 3]}.

In the study and analysis of his writings a fascinating internal contradiction emerges regarding his attitude to the transmigration of souls: whereas in the book "Hegyon ha-Nefesh ha-Atzuvah" he counts transmigration as one of the possible paths for the rectification of the souls of sinners, in the book "Megillat ha-Megalleh" (and in other parts of "Hegyon ha-Nefesh") he rejects this doctrine utterly and calls it nonsense and great vanity ^{[cite: 3, 15]}. He explains that the idea of the return of the first body at the resurrection of the dead does not accord with the philosophical concept of a constant transmigration of souls between different bodies of living creatures ^{[cite: 15]}. Scholars such as Simon emphasized that because of the popular and homiletic character of his books, one should not expect to find in them an entirely closed philosophical system free of contradictions, but rather an eclectic combination directed at the didactic and moral needs of his target audience at the time ^{[cite: 16]}.

The metaphysical fate of the souls is divided into four clear categories, as shown in the following table:

Eschatology, Calculating the End, and the Historiosophy of Redemption

Bar Chiya's monumental eschatological book, "Megillat ha-Megalleh," is the first systematic work in Europe written by a rabbi with the aim of calculating the end of days and the redemption in a combined scientific and theological manner ^{[cite: 7]}. The book reflects the historical and spiritual pressures experienced by the Jewish communities in the region of Barcelona and southern France during the first Crusades, a period in which the question of redemption and national survival became most urgent ^{[cite: 3]}.

Cyclical Astrology and Cultural Influences

In the book Bar Chiya lays out a wide-ranging historiosophical theory that compares the seven days of creation to seven historical eras of the history of mankind ^{[cite: 7]}. The course of the empires, the rise and fall of dynasties and the religious wars between Christianity and Islam he explains by means of the cosmic cycles of conjunction of the planets Jupiter and Saturn ^{[cite: 3]}. In his view, the constellations and the stars act as physical instruments by means of which the Creator guides human history ^{[cite: 3, 13]}.

According to his astronomical calculations and his interpretation of the Book of Daniel (especially around the verses of the 1335 days), he fixed the year 1358 CE (the year 158 of the fifth millennium) as the year of the beginning of the redemption, the year 1383 CE as the year of the coming of the Messiah, and the year 1448 CE as the year of the resurrection of the dead ^{[cite: 7, 17]}. The influence of these calculations was immense, and they served as a source of inspiration for Nahmanides (Ramban), for Ralbag, for Rabbenu Bachya ben Asher and for Rabbi Ishtori ha-Parchi, who adopted the difference of 45 years found in Daniel in order to update their predictions of the redemption to suit their own time ^{[cite: 17]}. Modern scholars such as Julius Guttmann suggested that these historiosophical conceptions of Bar Chiya were also influenced to some degree by the thought and writings of one of the Fathers of the Christian Church, Isidore of Seville, which testifies to Bar Chiya's intellectual openness to absorbing ideas from his general cultural environment ^{[cite: 3]}.

His Historical Testimony on the Temple Mount and the Site of the Temple

Apart from his theoretical concern with the end of days, "Megillat ha-Megalleh" includes historical testimony of the first order concerning the Temple Mount and the site of the Temple in the Middle Ages ^{[cite: 18, 19, 20]}. Bar Chiya describes how, after the destruction of the Temple by the Romans, Jews were not prevented from entering the Mount for the purpose of prayer ^{[cite: 18, 19, 21]}. Moreover, he testifies that under the rule of Islam the rulers treated the Jewish community with generosity and permitted them to build a house of prayer and study on the Temple Mount itself ^{[cite: 18, 19, 21]}. Jews from all the nearby lands of the Jewish dispersion would go up on pilgrimage on the festivals and holy days, and pray facing the site of the Temple in place of the daily and additional offerings ^{[cite: 18, 19, 21]}.

This situation changed completely with the conquest of Jerusalem by the Crusaders ("the wicked kingdom of Edom"), who expelled the Muslims and the Jews, desecrated the place, turned the buildings on the Mount into Christian houses of prayer and set up statues in them ^{[cite: 18, 21, 22]}. This testimony is regarded as a decisive halakhic and historical document in modern halakhic discussions dealing with the boundaries of the Temple Mount and the tradition of entering it in past generations, and it is cited at length alongside the testimonies of Maimonides (Rambam) and Nahmanides (Ramban), who also went up to Jerusalem and prayed at the site of the Temple ^{[cite: 19, 20, 21]}.

His Scientific Work and the Linguistic Revolution

Bar Chiya's contribution to science is not confined to mere translation; he is regarded as the first mathematician in Europe to bring the tidings of Arabic algebra and trigonometry to Western culture ^{[cite: 5, 11]}.

Breakthroughs in Mathematics and Geometry

His book "Chibbur ha-Meshichah ve-ha-Tishboret" (Treatise on Measurement and Calculation) was originally written to serve as a practical guide for the Jews of France, who had difficulty measuring the boundaries of their fields for the purpose of calculating the division of lands and taxes ^{[cite: 5, 7]}. The book presents for the first time in Europe a complete, systematic and proven solution of the general quadratic equation of the type: $$ax^2 + bx + c = 0$$ ^{[cite: 5, 11]}.

The book also presents the famous mathematical proof of the relation between the circumference of a circle and its area ^{[cite: 5]}. His argument is based on unfolding the circle into an infinite collection of concentric circles, which are straightened and opened out along the radius ($r$) to form a right-angled triangle ^{[cite: 5]}. The height of this triangle is equal to the radius of the circle ($r$) and its base is equal to the circumference of the outer circle ($C = 2\pi r$) ^{[cite: 5, 7]}. By calculating the area of the triangle: $$S = \frac{1}{2} \cdot \text{base} \cdot \text{height} = \frac{1}{2} \cdot (2\pi r) \cdot r = \pi r^2$$ he proves the formula for the area of a circle ^{[cite: 5, 7]}. A further breakthrough in the book is the presentation of the formula for calculating the volume of a truncated pyramid, a unique mathematical achievement not documented in the written literature since an ancient Egyptian papyrus of the 18th century BCE ^{[cite: 7]}. The translation of this book into Latin under the title Liber Embadorum by Plato of Tivoli in 1145 became one of the pillars of mathematical education in Western Europe, and was the principal source from which Fibonacci copied conclusions, ideas and examples for his well-known book "Practical Geometry" (Practica Geometriae) ^{[cite: 5, 6, 7]}. Echoes of his work reached even the notebooks of Leonardo da Vinci, who explicitly noted the Hebrew origin of the work ^{[cite: 23]}.

The Science of Intercalation and the Sanctification of the Month

Bar Chiya's "Sefer ha-Ibbur" (Book of Intercalation), written in 1123, is regarded as the most comprehensive and thorough work in the field of the Hebrew calendar up to his time ^{[cite: 5, 8]}. The historiographical importance of the book is immense, since in it is documented for the first time the tradition attributed to Rav Hai Gaon, according to which Hillel II (Hillel son of Rabbi Yehuda Nesiah) instituted the fixed rules of intercalating the year that are in use today, in the year 359 CE (the year 670 of the Seleucid era) ^{[cite: 8, 24]}. This tradition, which was later adopted by Nahmanides (Ramban) in "Sefer ha-Zekhut," became the accepted historical foundation in Jewish communities, even though modern discoveries from the Cairo Genizah show that the calendar continued to develop and change in later periods as well ^{[cite: 8]}.

In this book Bar Chiya made extensive use of ancient baraita literature such as the "Baraita de-Shmuel," which he identifies with the work "Pirkei de-Rabbi Eliezer," and thereby saved ancient calendrical traditions from oblivion ^{[cite: 15]}. The book won lavish praise from Maimonides (Rambam), who noted that its scientific level far surpasses all the works composed in the East on the same subject ^{[cite: 5]}.

Establishing Scientific Hebrew and the Defense of Astrology

Before Bar Chiya's time, the Hebrew language served mainly for sacred purposes, liturgical poetry and halakha, while books of science and philosophy were written in Arabic ^{[cite: 5]}. Bar Chiya had to bring about an unprecedented linguistic revolution in order to make the sciences accessible to the Hebrew reader ^{[cite: 5]}. In his famous introduction to his encyclopedia "Yesodei ha-Tevunah u-Migdal ha-Emunah" (The Foundations of Understanding and the Tower of Faith), he explains that he did this out of a moral obligation to the sages of France, who did not command the Arabic language ^{[cite: 5, 25]}. He uses verses from the Book of Jeremiah (9:22-23), Proverbs and Job to prove that the investigation of nature and the sciences does not contradict faith but is the necessary instrument for attaining true knowledge and fear of God ^{[cite: 25]}.

The linguist Gad Ben-Ami Sarfatti defined him as the first craftsman to expand the boundaries of the Hebrew language systematically ^{[cite: 5]}. Bar Chiya created precise mathematical and philosophical terms based on original biblical and Talmudic roots, while pouring into them the content of the Arabic terms (calques) ^{[cite: 5]}. This linguistic infrastructure, which was studied at length by linguists such as Israel Efros and Hanoch Gamliel, served as a solid foundation for the translators who came after him, such as the Ibn Tibbon family and Rabbi Abraham ibn Ezra ^{[cite: 3, 5, 16]}.

This linguistic and scientific revolution also found expression in his complex attitude to astrology ^{[cite: 5, 13]}. In his letter to Rabbi Yehuda ben Barzilai of Barcelona, he fervently defends the legitimacy of scientific astrology ^{[cite: 3, 5, 13]}. He explains that the motion of the constellations is a fixed physical law that the Creator planted in creation, and that the prohibition "You shall not practice soothsaying" applies only to one who attributes independent powers to the constellations apart from the will of the one God ^{[cite: 5, 13]}. By combining science and theology, he shows that the free choice and righteousness of the people of Israel enable them to rise above the celestial laws of nature, and thus the halakhic principle "Israel is not subject to the constellations" (ein mazal le-Yisrael) is fulfilled, not because the astrological system does not exist, but because Israel has the spiritual tools to rise above it ^{[cite: 13]}.

Summary and Assessment of His Historical Influence

Rabbi Abraham bar Chiya ha-Nasi stood at a unique historical crossroads, and his Torah and scientific teaching left an indelible mark on many generations ^{[cite: 5]}. He embodied in his personality the perfect synthesis of a man of halakha and public leader together with being a pioneering scientist, mathematician and astronomer of international standing ^{[cite: 1, 3, 5]}.

His influence is evident along two parallel tracks: in the Jewish world, his books in the fields of intercalation, astronomy and philosophy were cited and studied by the great Rishonim, among them Maimonides (Rambam), Nahmanides (Ramban), Ibn Ezra, Radak, the Meiri and Abarbanel ^{[cite: 5, 7, 8]}. In the general world, his translations and studies laid the foundations for the arrival of Arabic algebra and trigonometry in Christian Europe, and directly influenced the great scientists of the Renaissance such as Leonardo Fibonacci ^{[cite: 5, 7]}. His work demonstrates how science and faith, far from being contradictory, can fertilize one another and create a harmonious worldview that defines the laws of nature as the practical expression of the divine will in the cosmos ^{[cite: 5, 13]}.