"If, then, you wish to insure the interest of your pupils, there is only one way to do it; and that is to make certain that they have something in their minds to attend with, when you begin to talk. That something can consist in nothing but a previous lot of ideas already interesting in themselves, and of such a nature that the incoming novel objects which you present can dovetail into them and form with them some kind of a logically associated or systematic whole."