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Ps-Rabanus’ commentary, known since Victor Cousin first referred to it, is the earliest commentary on Porphyry’ Isagoge that was very influential in the beginning of the scholastic logic. The four extant manuscripts give us considerably different versions. Together with a critical edition of each version, this article argues that it was, in its original, a work by William of Champeaux in the late 11th century, and revised by his students in the very early 12th century.