Didascalicon, Book III: the art of study (discipline and method)
Chapter VI. What should be assigned to each art
There is another error, not much less than this, which must be avoided with the greatest care. For there are some who, although they omit nothing of what is to be read, know not how to assign to any art what is its own, but read all things in each. In grammar they dispute about the reason of syllogisms, in dialectic they inquire into the inflections of cases, and, what is more worthy of derision, at the title they read almost the whole book, and scarcely get through the third reading when they begin. They do not teach others in this way, but display their own knowledge. But would that they appeared to everyone as they do to me! Observe how perverse this custom is; since surely the more superfluous things you gather, the less can you take in or retain the useful ones. In any art, then, two things are chiefly to be discerned and distinguished by us: first, how one ought to proceed within the art itself; second, how one ought to adapt the reasons of the art itself to any other matters. There are two things: to treat of the art, and to act by the art. For example, to treat of an art, as to act grammatically. He treats of grammar who handles the rules given about words and the precepts pertaining to the word; he acts grammatically who speaks or writes by rule. To treat of grammar, therefore, belongs only to certain persons, as Priscian, Donatus, Servius, and the like. To act grammatically belongs to all. When, therefore, we treat of any art, especially in teaching, where all must be restricted to compendium and recalled to easy understanding, it ought to suffice to explain what is being treated as briefly and aptly as possible, lest, if we multiply foreign reasons too much, we disturb the reader rather than edify him. Not all things that we can say are to be said, lest what we ought to say be said less usefully; in each art seek at last what is established as pertaining specially to it. Then, when you have read the arts, and have learned by disputing and comparing what is proper to each, then at last it will be permitted to compare the reasons of each with the others, and by alternate consideration to investigate in turn what you had previously understood less. Do not multiply by-ways until you have learned the paths: you will run about securely when you do not fear to err.