Canonization
The Ketuvim is the last of the three portions of the Tanakh to have been accepted as Biblical canon. While the Torah may have been considered canon by Israel as early as the 5th century BCE and the Former and Latter Prophets were canonized by the 2nd century BCE, the Ketuvim was not a fixed canon until the 2nd century of the Common Era.
Evidence suggests, however, that the people of Israel were adding what would become the Ketuvim to their holy literature shortly after the canonization of the prophets. As early as 132 BCE we have references suggesting that the Ketuvim was starting to take shape, though it lacked a formal title. We also know from references in the four Gospels as well as other books of the New Testament that many of these texts were both commonly known and counted as having some degree of religious authority early in the 1st century CE.
Many scholars believe that the limits of the Ketuvim as canonized scripture were determined by the Council of Jamnia c. 90 CE. Indeed, Against Apion, the writing of Josephus in 95 CE, treated the text of the Hebrew Bible as a closed canon to which "... no one has ventured either to add, or to remove, or to alter a syllable..." However, we know that for a long time following this date that the divine inspiration of Esther, the Song of Songs, and Ecclesiastes was often under scrutiny.
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