structural:expansion, information:extraction, stylistic:style_transfer
Canonical differences

The Septuagint does not consist of a single, unified corpus. Rather, it is a collection of ancient translations of the Tanakh, along with other Jewish texts that are now commonly referred to as apocrypha. Importantly, the canon of the Hebrew Bible was evolving over the century or so in which the Septuagint was being written. Also, the texts were translated by many different people, in different locations, at different times, for different purposes, and often from different original Hebrew manuscripts.

The Hebrew Bible, also called the Tanakh, has three parts: the Torah ("Law"), the Nevi'im ("Prophets"), and the Ketuvim ("Writings"). The Septuagint has four: law, history, poetry, and prophets. The books of the Apocrypha were inserted at appropriate locations. Extant copies of the Septuagint, which date from the 4th century CE, contain books and additions not present in the Hebrew Bible as established in the Jewish canon and are not uniform in their contents. According to some scholars, there is no evidence that the Septuagint included these additional books. These copies of the Septuagint include books known as anagignoskomena in Greek and in English as deuterocanon (derived from the Greek words for "second canon"), books not included in the Jewish canon. These books are estimated to have been written between 200 BCE and 50 CE. Among them are the first two books of Maccabees; Tobit; Judith; the Wisdom of Solomon; Sirach; Baruch (including the Letter of Jeremiah), and additions to Esther and Daniel. The Septuagint version of some books, such as Daniel and Esther, are longer than those in the Masoretic Text, which were affirmed as canonical in Rabbinic Judaism. The Septuagint Book of Jeremiah is shorter than the Masoretic Text. The Psalms of Solomon, 1 Esdras, 3 Maccabees, 4 Maccabees, the Letter of Jeremiah, the Book of Odes, the Prayer of Manasseh and Psalm 151 are included in some copies of the Septuagint.

The Septuagint has been rejected as scriptural by mainstream Rabbinic Judaism for a couple of reasons. First, the Septuagint differs from the Hebrew source texts in many cases (particularly in the Book of Job). Second, the translations appear at times to demonstrate an ignorance of Hebrew idiomatic usage. A particularly noteworthy example of this phenomenon is found in Isaiah 7:14, in which the Hebrew word עַלְמָה (‘almāh, which translates into English as "young woman") is translated into the Koine Greek as παρθένος (parthenos, which translates into English as "virgin").

The Septuagint became synonymous with the Greek Old Testament, a Christian canon incorporating the books of the Hebrew canon with additional texts. Although the Catholic Church and the Eastern Orthodox Church include most of the books in the Septuagint in their canons, Protestant churches usually do not. After the Reformation, many Protestant Bibles began to follow the Jewish canon and exclude the additional texts (which came to be called the Apocrypha) as noncanonical. The Apocrypha are included under a separate heading in the King James Version of the Bible.