Coming in contact with high officials and ecclesiastical dignitaries, Joseph, like his father, was often invited to take part in religious controversies, in which he acquired great skill.
Accounts of these controversies, together with those of his father and of some French rabbis, were collected by Joseph in a work entitled Yosef ha-Meqanne or Teshubot ha-Minim, which is still extant in manuscript (Paris, Bibliothèque Nationale, Hebr.
All the Christian dogmas which are derived from scriptural texts, such as the immaculate conception, the divinity of Jesus, his mission on earth, his birth, death, and resurrection, are analyzed and discussed; and there occur refutations of some attacks on Judaism, such as the accusation of ritual murder, which the chancellor endeavored to base upon Num.
The characteristic feature of these controversies, which in the main have no claim to great originality as regards the arguments used, is the freedom of speech and boldness displayed by the Jewish participants, who do not content themselves with standing upon the defensive, but very often attack their opponents not with dialectics, but with clever repartee.
Of this kind of controversy the following may serve as examples: Nathan ben Meshullam was asked to give a reason for the duration of the present exile, while that of Babylon, which was inflicted upon the Jews as a punishment for the worst of crimes, idolatry, lasted only seventy years.
Elijah, Joseph ben Nathan's brother, was asked by the chancellor why the Mosaic law declared contact with, or being in the presence or neighborhood of, a dead body to be a cause of impurity.
Joseph seems to have been the author also of a commentary on the Pentateuch, and of the Hebrew version of the controversy of Jehiel of Paris, at the end of which is a short poem containing his initials.