The third definition is this: 'Nature is an artisan fire, proceeding from a certain power for the procreation of sensible things.' For the natural philosophers say that all things are procreated from heat and moisture; whence Virgil calls Ocean 'father,' and Valerius Soranus, in a certain verse concerning Jupiter understood as the ethereal fire, says: 'Almighty Jupiter, begetter of things and of kings, father and mother of the gods, truly one and the same.' On the origin of logic. Therefore, since we have now demonstrated the origin of the theoretical, the practical, and the mechanical, it remains to investigate also the origin of logic, which I number last for this reason: that it was discovered last.
The others had been discovered earlier, but it was necessary that logic too be discovered, since no one can suitably discourse about things unless he has first come to know the method of speaking rightly and truthfully. For as Boethius says: 'When the ancients first bestowed their effort upon investigating the natures of things and the qualities of conduct, it was necessary that they often be deceived, because they did not have the discrimination of words and concepts'—as happened in many cases to Epicurus, who supposes that the world consists of atoms and falsely makes pleasure to be the honorable good. That this befell him and others is manifest for this reason: that through inexperience in disputing, whatever they had grasped by their reasoning, this they judged to come about in the things themselves as well.
But this is a great error. For things do not stand in reasonings as they do in numbers. For in numbers, whatever comes out on the fingers of one who computes rightly, this without doubt must also come out in the things themselves; so that if from a reckoning a hundred results, it is necessary that there be a hundred things subject to that number. But this is not equally preserved in disputation. For not whatever the course of words has found is thereby held fixed in nature. Wherefore it is necessary that those be deceived who, casting aside the science of disputing, would inquire into the nature of things.
For unless one first arrives at the science by which it may be known which reasoning holds the true path of disputing, which holds the merely probable, and recognizes which is to be trusted and which may be suspect, the uncorrupted truth of things cannot be discovered by reasoning. Since, then, the ancients, often lapsing into many errors, would gather to themselves in disputation certain false and contradictory things—and since it seemed impossible that, when a contradictory conclusion was drawn about the same matter, both should be true which their disagreeing reasoning had concluded, and it would be doubtful which reasoning ought to be believed—it seemed good first to consider the true and entire nature of disputation itself.
And once this was known, then also whatever was discovered through disputation could be understood as to whether it had been truly grasped. Hence, therefore, set forth the expertise of the discipline of logic, which prepares the modes of disputing and the very ways of distinguishing reasonings, so that one may recognize which reasoning is now true and now false, which is always false, and which can never be false. This discipline is indeed last in time, but first in order. For it is to be read first by those beginning philosophy, because in it is taught the nature of words and concepts, without which no treatise of philosophy can be reasonably unfolded. Logic is so called from the Greek 'logos,' which name has a twofold interpretation.
For 'logos' means 'speech' or 'reason,' and from it logic can be called either the verbal or the rational science. Rational logic, which is called argumentative (dissertiva), contains dialectic and rhetoric. Verbal logic is the genus with respect to grammar, dialectic, and rhetoric, and contains under itself the argumentative. And this is the verbal logic which we number as the fourth after the theoretical, the practical, and the mechanical. Nor should it be thought that logic—that is, the verbal—is so called because before its discovery there were no discourses, and as if men had not previously had mutual conversations. There existed beforehand both common discourses and letters, but the method of discourses and letters had not yet been reduced into an art.
No precepts for speaking or disputing rightly had yet been given. For all the sciences existed in use before they existed in art. But then men, considering that use could be converted into art, and that what had been wandering and unregulated before could be confined by fixed rules and precepts, began, as has been said, to reduce to art the custom which had arisen partly by chance, partly by nature—correcting what use had crooked, supplying what it lacked, cutting away what it had in excess, and henceforth prescribing fixed rules and precepts for each thing. Of this kind was the origin of all the arts; running through these one by one, we find it to be true. Before there was grammar, men both wrote and spoke.
Before there was dialectic, men distinguished the true from the false by reasoning. Before there was rhetoric, they handled civil law. Before there was arithmetic, they had the science of counting. Before there was music, they sang. Before there was geometry, they measured fields. Before there was astronomy, they took the divisions of times by the courses of the stars. But the arts came—which, although they took their beginning from use, are nevertheless better than use. This would be the place to set forth who were the inventors of the several arts, when or where they lived, or how through them the beginning of these disciplines was taken; but I wish first, by a certain division of philosophy, to distinguish them one from another.
It is fitting, therefore, briefly to recapitulate what has been said above, so that the transition to what follows may be made easier. We have said that there are only four sciences which contain all the rest: namely, the theoretical, which labors in the contemplation of truth; the practical, which considers the discipline of conduct; the mechanical, which dispenses the actions of this life; and logic also, which furnishes the science of speaking rightly and disputing acutely. Here, then, not absurdly, can that quaternary of the soul be understood, which the ancients, out of reverence for it, took up into their oaths. Whence also that saying: 'By Him who gave to our soul the number four.'
How these are contained under philosophy, and again which things they contain under themselves, we shall show by briefly repeating the definition of philosophy.