He wrote
commentaries on the books of
Joshua,
Judges and
Samuel,
Kings and
Job. MSS. Nos. 217 and 218, in the Bibliothèque Nationale, Paris, contain commentaries by him on the prophetical books and on
Psalms; the Rome MSS. contain a commentary on the
five Megillot. The last-named are sometimes ascribed to his grandfather, but
Güdemann advances several reasons in support of Isaiah ben Elijah's authorship, the principal being their identity of style with Isaiah's acknowledged commentaries.
Gilbert Génébrard published a Latin translation of di Trani's commentary to
Song of Songs in 1585 (the commentary was identified by
H. J. Matthews in 1880). Isaiah's commentaries are confined to simple, concise, and rational
exegesis. Their importance lies in the fact that they were the first to be issued in
Italy that were free from allegorical interpretations. In them he quotes the Spanish grammarians
Ibn Janaḥ,
Ibn Ḥayyuj, and
Abraham ibn Ezra. More important, however, is his
Pirkei Halakhot, a ritual code, the first produced in Italy. Extracts from it are printed in
Joshua Boas's
Shilṭe ha-Gibborim, Sabbionetta, 1554, and in the editions of
Isaac Alfasi's
Halakhot. On the basis of the
Talmudical treatises and following their sequence the
Halakot are derived from the
Mishnah rather than from the
Gemara, and are clearly arranged in a precise way. The author ascribes great authority to the
Jerusalem Talmud. He is independent in his criticisms of older authorities, his grandfather not excepted, whom he often quotes (with the abbreviation מז"ה = "Mori Zeḳeni ha-Rav"). As a sort of preliminary work to the
Halakhot he wrote a book, ''Kontres ha-Re'ayot,'' which contained and discussed the proofs for his halakic decisions. Isaiah also wrote a
Tachanun prayer. Two other prayers, signed merely "Isaiah", Unlike his grandfather, Isaiah was an opponent of
Aristotle and of the rest of the
Greek philosophers who "denied the Torah." Religious conceptions are, according to him, a matter of tradition more than of individual meditation. He advised against religious disputations with the
Gentiles and against teaching them the
Torah. He endeavored to shield the grotesque
midrashim from derision on the part of
Christian theologians and baptized Jews by interpreting them as symbolic or hyperbolic. ==References==