Chapter XI: Book II: Demonstrativa and Dialectica

_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 my judgment, really pursue, neither aspires to dogma, nor is drowned in the waves of politics, but analyzes truth by prompt and reasonable probability.”

iv. _Dialectica_, moreover, is the art of effective debate.

v-viii. _Logica_ has for its distinctive function to serve as effective instrument. It is not an end in itself. So perverted, it becomes the absurd and deplorable occupation of senility.

ix-xi. (866 C) “_Dialectica_, which among the servants of eloquence is most alert and prompt, avails each man according to the measure of his knowledge.... Deprived of the strength of the other disciplines, it is maimed and almost useless; thriving with their vigor, it is strong to overthrow all falsehood, and always suffices at least to reach a probable conclusion.” From my own teachers, to whom I returned years after they had schooled me, I conclude that “as _dialectica_ advances other disciplines, so if it remain alone, it lies bloodless and sterile, and does not engender the fruit of philosophy in a soul not impregnated from other sources.” Of itself it can only despatch issues, not rise to others.

xii. _Dialectica_ operates in all disciplines wherever the issue is abstract.[36] It leaves to _rhetorica_ whatever is hypothesis, i.e., whatever involves concrete circumstances: who, what, when, why, how. It makes no address to the public, expects no legal decision.

xiii-xv. Though each division of philosophy has its own field of inquiry and its own principles, yet _logica_ supplies methods common to all, as it were theory in a nutshell. A problem in _dialectica_ considers choice and avoidance, truth and knowledge, whether for itself or as aiding inquiry where opinion divides.

xvi-xvii. Review of the value and place of Aristotle, of the right use of Porphyry’s Introduction, and of other typical cases in teaching. Bernard (875 D) of Chartres and his followers took great pains to heal the breach between Plato and Aristotle; “but in my opinion they came late and labored in vain to reconcile in death those who differed as long as they lived.”

xviii-xix. Certain errors of those who profess Aristotle can hardly be overlooked: the burdening of tender shoulders, the making of Porphyry cover the whole ground, the misinterpretation that simplifies Aristotle by substituting Plato or something remote from both.

xx. The last chapter, much the longest, presents Aristotle on genus and species.