Characteristics
Hai was not only a master of Hebrew lore, but was also familiar with the Quran and the Hadith, with Plato, Aristotle, Alfarabi, the grammarian al-Halil, the Septuagint, the Greek calendar, Greek history, and the Persian language translation of Kalilah wa-Dimnah. He did not hesitate to consult even the Catholicos of the Assyrian Christians in an exegetical difficulty over Psalms cxli. 5, as the Sicilian dayyan Matzliah ibn al-Basak relates in his biography of Hai. Hai justified his action by saying that scholars in former times did not hesitate to receive explanations from those of other beliefs. He had an exact knowledge of the theological movements of his time, of which that of the orthodox Ash'ariyyah attracted him the most. Moses ibn Ezra, in his Poetik (fol. 1196), even called him a Mutakalam. He was also competent to argue with Muslim theologians, and sometimes adopted their polemical methods. Hai was orthodox as regards tradition, and upheld minhag to its fullest extent. He established the principle that where the Talmud gives no decision traditional customs must be adhered to. He even went so far as to recommend the observance of every custom not in direct opposition to law. In many passages of his responsa he warns against deviating from a custom even when the meaning of its origin has been lost, as in the case of the practice of not drinking water during the Tekufot. But this did not prevent him from opposing the abuses common to his time. Thus he protested against the practice of declaring null and void all oaths and promises which may be made during the coming year, and against the refusal to grant an honorable burial to excommunicated persons and their connections
Hai's conservative standpoint explains the fact that in the study of esoteric sciences he detected a danger to the religious life and a deterrent to the study of the Law. He warned against the study of philosophy, even when pursued with the plea that it leads to a better knowledge of G-d.
Of his own views on religious-philosophical subjects only those regarding the anthropomorphisms of the Bible (expressed in his appeal to a well-known dictum of R. Ishmael: "The Torah spoke in language of men") and one or two other subjects were known prior to the publication of ibn Balaam's commentary on the Book of Isaiah. A responsum of Hai given in this commentary discloses his opinion on the subjects of divine fore-knowledge and the predestined length of human life. The essence of divine prescience seems to consist, according to him, in a preknowledge of both hypothetical and actual occurrences. In this he shows the influence of Saadia.
His attitude toward the Kabbalah is determined by his conservative standpoint. Its elements, as far as they can be traced back to the Talmud, he considered to be true. When the inhabitants of Fez made inquiries regarding the proportions of God, he answered, as one of the signers of the responsum, that God is above any corporeal qualification and that the Talmud forbids the public discussion of these things. His answer to the question regarding the interpretation of the Talmudic tradition that four men entered paradise is interesting, and has caused much discussion. He refers to the opinion of various scholars that specially favored persons could attain, by means of castigation and the reciting of psalms, to an ecstatic state in which they might behold the heavenly halls ("hekalot") as vividly as if they really had entered them. Contrary to his father-in-law, Samuel ben Hofni, gaon of Sura, he followed former scholars in deeming it not impossible that God should reveal the marvels of heaven to the pious while in this state of ecstasy. But all the elements of the later Kabbalah not found in Talmudic tradition, as the belief that miracles could be performed with the names of God, he designated as foolishness not credited by any sensible man.
The best characterization of Hai is given by Steinschneider;: "Certain Kabbalistic pieces were ascribed to him; but in truth he was no mystic in the usual sense of the word. In fact he fought against superstition. He was an orthodox Jew, in possession of general culture, but hostile to deeper philosophical research."
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