Reference edition:

Anicii Manlii Seuerini Boethii De diuisione liber, critical edition, translation, prolegomena and commentary by John Magee, Leiden-Boston-Köln, Brill, 1998.

This treatise, which John of Salisbury knew and considered the most elegant of Boethius’ logical treatises (Metalog.; PL 199: 909), was presumably composed between 515 and 520 AD (Magee 1998); Boethius himself mentions it explicitly in the De topicis differentiis (PL 64: 1192).  Division - together with definition, syllogism, and sophism - represents one of the primary elements of the logic of discourse; in his treatment, Boethius explains and synthesizes the three primary conceptions of division: the Platonic, the Aristotelian, and the Stoic.  For Plato, division is the second step of the dialectic process, which both consists of dividing an idea into its different types by indicating the characteristics that distinguish those types from one another and aids in the formulation of correct definitions (Soph. 222B and 253D).  Aristotle criticizes Plato’s division in his Prior Analytics on the grounds that it treats as a presupposition the very thing one actually needs to prove (An. Pr. 1.46a).  Stoic doctrine, which rehabilitated dialectic, gives new importance to division as an instrument capable of grasping the relationships between elements of language: in particular, it consists of the technique of dividing a general type in its most closely related sub-types (Diog. Laert. 7.1.61-2).  Boethius analyzes these different types of division, indicating the properties and reciprocal differences of each, in order to elucidate the differences between division of a general type from its sub-types and other sorts of division that separate a subject from its accidents.  Division of the general type from its sub-types, in fact, concerns the real essence of things and is a true logical division that allows one to arrive at definitions that capture the ontological dimension of reality.

Medieval schools frequently used this treatise to teach dialectic, and it thus enjoyed a wide diffusion from the end of the 10^th c. AD: it is attested in at least 197 manuscripts, a number that is only surpassed among works of Boethius by the Consolatio Philosophiae, by far his most famous work (Magee 1998).  In the proem to this work, Boethius also mentions two texts that are otherwise unknown to us: an essay on Andronicus of Rhodes’ De divisione and a commentary on Plato’s Sophist written by Porphyry (PL 64: 875).  [M. Ferroni; tr. C. L. Caterine].