54. In the same way, if all minute and technical details (such as the species of plants and of animals, the various callings of mechanics, the names of all their tools and so forth) had to be learned, this would be a most wearisome and confusing task. In school-work it is sufficient if the wide classes that exist in nature, with their most important and most essential divisions, be made thoroughly clear. More specialised knowledge can easily be acquired later, as the opportunity arises.
Those who wish to win a speedy victory over the enemy, do not waste time in storming unimportant places, but go straight to the head-quarters of the war; since it is certain that, if they can get the upper hand in a pitched battle, and capture the most important strongholds, all the others will surrender of their own accord. In the same way, if the principal points of any subject be mastered, the subsidiary details will be acquired with great ease. To this class of obstructions belong the voluminous dictionaries that contain every word in a language. For, since the greater number of them are never used, why should we force boys to learn them all, and thus overburden the memory?
We have now treated of the saving of time and effort in teaching and in learning.
