What one fails to do, must either be done by an other, or left undone.

After much observation, it seems to me, that the most proper mode of treating this science in schools, is, to throw the labour of its acquisition almost entirely upon the students; to require from them very accurate rehearsals as the only condition on which they shall be listened to; and to refer them to their books for the information which they need, and in general for the solution of all their doubts.

But then the teacher must see that he does not set them to grope their way through a wilderness of absurdities.

He must know that they have a book, which not only contains the requisite information, but arranges it so that every item of it may be readily found.

That knowledge may reasonably be required at their recitations, which culpable negligence alone could have prevented them from obtaining.
6.