_Proem._ “The course of the former book has sufficiently, I think, disengaged the truth that _grammatica_ is not useless, and that without it not only eloquence falls short, but the way toward the other expressions of philosophy is not open.” i. _Logica_, being the theory of discourse, embraces both investigation and judgment.[32] ii. Knowledge of truth being for them the highest good, the Peripatetics divided philosophy into two parts: natural, or physical, and moral, or ethical.[33] But the difficulties arising from insufficient control of discourse “demonstrated the need of determining and publishing a lore which should distinguish words and concepts[34] and dissipate the mists of fallacies. Here, indeed, as Boethius asserts in his second commentary on Porphyry, is the origin of the _logica disciplina_. For there had to be a lore which should distinguish the true from the false and teach which reasoning holds the path of [absolute] truth, which of probable, which of assumed,[35] and which should be distrusted. Otherwise truth cannot be found by reasoning (858 C).... The rules of the art were seized and handed down finally by Aristotle.” iii. (859 C) “Later in time than the other disciplines of philosophy, this is first in place. For beginners in philosophy it is a prerequisite, as the interpreter of words and concepts, without which no item of philosophy comes precisely to light. He who thinks that philosophy is taught without _logica_, i.e., by [direct] cultivation of wisdom, may as well do away with theory in everything, since this is the domain of _logica_.... The very name comes from its being an aid and a test of theory. Plato divided it into _dialectica_ and _rhetorica_; but those who estimate its efficacy higher give it more, i.e., _demonstrativa_, _probabilis_, _sophistica_. _Demonstrativa_ begins in the first stages of training, and passes on into the next. It is satisfied only by necessity; provided a thing ought to be so, it pays little attention to whether or not it appears to be so. This becomes the philosophical majesty of those who are teaching precisely, a majesty grounded, quite apart from the assent of an audience, on its own will. _Probabilis_, on the other hand, is occupied with what appears to be so to all, or to many, or to intelligent observers, with what is best known and most probable to them, or with what follows therefrom. This includes _dialectica_ and _rhetorica_, since logician and orator alike striving to persuade, the one an opponent, the other a judge, think the [abstract] truth of their arguments makes little difference, provided they keep what seems to be true. But _sophistica_, which is apparent and not serviceable wisdom, assumes the likeness either of probability or of necessity, little caring what this or that may be, while it involves whatever is discussed in fanciful images and deceptive shadows. _Dialectica_, that member of the Trivium which all approach from this side and from that, but few, in