Joseph was on very friendly terms with his teacher Jacob Tam, with whom he carried on a learned correspondence.
[4] Besides tosafot on the greater part of the Talmud, Joseph wrote a notable Biblical commentary.
Anticipating later Biblical criticism, he assumed the presence of duplicate narratives in the Bible,[5] and he strove to give rational explanations to the miraculous stories.
[6] Well acquainted with the Vulgate and Christian Biblical exegesis, Joseph, in commenting on Psalm 2, cites Jerome, whose explanation of the word "bar" (in Aramaic: "son") he criticizes.
He was explicitly anti-Christian, as shown by his commentaries on Genesis 1:26 (against the belief in the Trinity), on Numbers 12:8 (against Christian allegorizing) and on Deuteronomy 13 (attempting to connect the magical powers of false prophets with the miracles of Jesus in the New Testament).