Reference edition:

Manlii Seuerini Boetii, Opera omnia, accurante J.-P. Migne, tomus posterior, Parisiis 1891, 793-832 (Patrologiae Latinae, 64).

The aim of this small work, which Boethius considered an introductory essay (PL 64.793), is to provide a summary account of the categorical syllogism. The first book, being dedicated to the concept of the proposition and its basic elements, collects and comments on a few issues drawn from the initial chapters of Aristotle’s Peri hermeneias: in particular, Boethius analyzes names, predicates, and oratio, as well as propositions and their appropriateness.  The second book, which contains a selection of arguments from the Analytica priora, treats the composition and rules of syllogisms, formal correctness, ways of converting the different types of syllogism, and consequentiality (Righi 1984).

Although Boethius’ chief source is Aristotle (PL 64.793C; 810B; 813C, etc.), he also refers to many other authors, e.g. Theophrastus and Eudemus (PL 64.813C); Porphyrius appears to be of special importance, at one point being called gravissimae vir auctoritatis (PL 64.814C).  Ammonius’ commentary on the Peri hermeneias informs various sections of the first book, while the second demonstrates many affinities with the commentaries on the Analytica priora that were written by Alexander of Aphrodisias, Ammonius, and Philoponus. Like the Greek commentators on Aristotle, Boethius proceeds from simple concepts (e.g. name, predicate, proposition) to more complex ones (e.g. syllogism) and analyzes the propositiones through successive distinctions.  He borrows from Alexander of Aphrodisias the concept of conversio per contrapositionem, which was never treated explicitly in Aristotle (Lee 1984).  We know that Boethius was familiar with Porphyrius’ introduction to the categorical syllogism (In isag. 1.15), but since that work is lost we are unable to determine how much it influenced his treatment of the topic (Thomsen 2008).

Dating the work poses certain problems. The style of the first book is similar to what we find in Boethius’ commentary on Porphyrius’ Isagoge, and the author refers explicitly to his own commentary on the Peri hermeneias, occasionally directing his reader to it for a more detailed treatment of a given theme (PL 64.795A, 797B, 810B; De Rijk 1964). On the other hand, Boethius’ first commentary on the Peri hermeneias makes no reference to the De syllogismo categorico, and although he alludes in his second commentary to books “quos de categoricis syllogismi conposuimus” (In Peri herm. 2.172.8), there is no way to determine whether this refers to the De syllogismo categorico, to the Introductio ad syllogismos categoricos, or to both.  While the principle of cross-referencing is not always apparent and thus does not allow us to determine the dating with absolute certainty, it is reasonable to suppose that the treatises on categorical syllogism were composed between the first and the second redactions of his commentary on the Peri hermeneias (De Rijk 1964).

The first book of the De syllogismo categorico makes no explicit reference to the second, and a few scholars have consequently wondered whether the second book of this work is actually a continuation of the Introductio ad syllogismos categoricos (Prantl 1855).  Despite the absence of direct references, the two books are bound together by deep linguistic and stylistic similarities: for example, in both books of the De syllogismo categorico, Boethius uses the term contraiacentes to identify propositions that have the same subject and the same predicate, but that differ in quantity and quality; in the Introductio, on the other hand, he calls them oppositae or angulares (Thomsen 2008).

The De syllogismo categorico has been transmitted by about 50 manuscripts, which can be dated to between the 10^th and the 15^th c.  Given the number of codices, their dating, and their geographical provenance, we may reasonably conclude that the work was rediscovered at the start of the Late Medieval period and reached its widest diffusion in the 12^th c., especially in central Europe (Thomsen 2008).  [M. Ferroni; tr. C. L. Caterine].