Exposition of Maimonides' Guide of the Perplexed, and refutations of some of Maimonides' theories.

Don Isaac b. Judah Abrabanel (1437–1508), statesman, philosopher, and biblical exegete. Born in Lisbon, Abrabanel received a broad education embracing Jewish religious philosophy beside the traditional disciplines, also the basic works of classical literature, and the writings of the foremost Christian theologians, he studied Talmud under Joseph b. Abraham Hayyun. He was among the first Jewish scholars to be familiar with the concepts of humanism and the world of the Renaissance and to reflect their influence. He matured early. While still a youth he composed a treatise on Providence and prophecy, Ateret Zekenim, and at the age of 25 gave discourses in the synagogue on the Book of Deuteronomy, which he subsequently committed to writing.

Like his father Judah, Abrabanel engaged successfully in both commerce and state finance. After his father died he succeeded him as treasurer of King Alfonso V of Portugal. His importance at court was not restricted to his official sphere of activities. Of a loan to the state of 12,000,000 reals raised from both Jews and Christians in 1480, more than one-tenth was contributed by Abrabanel himself. When in 1471, two hundred fifty Jewish captives were brought to Portugal after the capture of Arcila and Tangier in North Africa by Alfonso V, Abrabanel headed the committee which was formed in Lisbon to raise the ransom money. As the Jews of Portugal were unable to maintain the captives unaided, Abrabanel asked Jehiel of Pisa to raise money for the purpose from Italian Jewry.

Abrabanel was also in touch with cultured Christian circles. His connections with members of the aristocracy were not founded only on business but also on the affinity of humanism. His letter of condolence to the count of Faro on the death of his father, written in Portuguese, provides a striking example of this relationship. The period of tranquillity in Lisbon ended with the death of Alfonso in 1481. His heir, JoCo II (1481–1495), was determined to deprive the nobility of their power and to establish a centralized regime. The nobles, led by the king's brother-in-law the duke of BraganLa and the count of Faro, rebelled against him, but the insurrection failed. Abrabanel was also suspected of conspiracy and forced to escape (1483). Although denying guilt, he was sentenced to death in absentia (1485). He evidently managed to transfer a substantial part of his fortune to Castile beforehand, and stayed there for a while in the little town of Segura near the Portuguese border. Abrabanel attributed his misfortunes to the fact that he had wasted his time in the service of an earthly ruler. He therefore decided to devote the rest of his life to religious study. The first task he set himself was to write a commentary on the earlier prophets, which the majority of exegetes had passed over, considering that his political experience should enable him to interpret them. He concluded his commentary on the books of Joshua, Judges, and Samuel within six months, but before he had finished his commentary on Kings he entered the service of Ferdinand and Isabella of Castile (1484). He was in AlcalF de Henares in 1488 and in 1491 in Guadalajara, where he visited the academy of Isaac Aboab II. The influential Abraham Senior of Segovia enlisted his cooperation in tax farming, and Abrabanel was allocated districts for this purpose in the central and southern parts of the country. His activities were of the widest scope: he loaned enormous sums of money to the royal treasury for special purposes, including 1½, million gold ducats to meet the cost of the war with Granada (1491–92). After the edict of expulsion of Spanish Jewry had been signed, on March 31, 1492, both Abrabanel and Senior tried in vain to obtain its revocation. Abrabanel relinquished his claim to certain sums of money which he had advanced to Ferdinand and Isabella against the tax farming revenues, which he had not yet managed to recover. In return he was allowed to take 1000 gold ducats and various gold and silver valuables out of the country with him (May 31, 1492).

Abrabanel sailed from the port of Valencia to Naples. Here he completed his commentary on Kings (fall 1493). But he was again prevented from devoting his time to study for long. The king of Naples Ferrante I appointed him to a position similar to that he had formerly held in Castile. Abrabanel continued in this after Ferrante's death in 1494, under his son Alfonso II. Abrabanel's home was looted when the French sacked Naples (1494), and his library which he had brought from Spain was destroyed. He now followed the royal family to Messina, remaining there until Alfonso died in June 1495. Subsequently he removed to Corfu where he began his commentary on Isaiah (summer 1495). On the French withdrawal from the kingdom of Naples, Abrabanel returned there and settled in Monopoli (Apulia), where early in 1496 he completed the commentary on Deuteronomy (Mirkevet ha-Mishneh), which he had begun in Lisbon, as well as his commentaries on the Passover Haggadah (Zevah Pesah), and on Avot (Nahalat Avot). Of the same period are his works expressing the hopes for redemption which explain contemporary events as messianic tribulations—Ma'yenei Yeshu'ah, Yeshu'ot Meshiho, and Mashmi'a Yeshu'ah. The summation of his religio-philosophical concepts is to be found in his exposition of Maimonides' Guide of the Perplexed, already begun while Abrabanel was in Spain, and in his refutations of some of Maimonides' theories, Shamayim Hadashim, Rosh Amanah (1505), and Mifalot Elohim. In 1503, at the suggestion of his son Joseph he settled at last in Venice. He was engaged in negotiations between the Venetian senate and the kingdom of Portugal in that year, for a commercial treaty to regulate the spice trade. He now finished his commentaries on Jeremiah (published 1504), the minor prophets, Genesis and Exodus (published 1505), and Leviticus and Numbers (published 1579). In a reply to an enquiry from Saul ha-Kohen of Candia in 1507, he mentions that he was engaged in composing his book Zedek Olamim, on recompense and punishment, and Lahakat ha-Nevi'im, against Maimonides' conceptions on prophecy (a new version of Mahazeh Shaddai which had been lost in Naples), and in completing his commentary on the Guide. Abrabanel died in Venice and was buried in Padua. Owing to the destruction of the Jewish cemetery there during the wars in 1509, his grave is unknown.