The two were congruent, but neither was subordinate. To know psychology, therefore, is absolutely no guarantee that we shall be good teachers. To advance to that result, we must have an additional endowment altogether, a happy tact and ingenuity to tell us what definite things to say and do when the pupil is before us. That ingenuity in meeting and pursuing the pupil, that tact for the concrete situation, though they are the alpha and omega of the teacher's art, are things to which psychology cannot help us in the least. The science of psychology, and whatever science of general pedagogics may be based on it, are in fact much like the science of war.
Nothing is simpler or more definite that the principles of either.
The principles being so plain, there would be nothing but victories for the masters of the science, either on the battlefield or in the schoolroom, if they did not both have to make their application to an incalculable quantity in the shape of the mind of their opponent. The mind of your own enemy, the pupil, is working away from you as keenly and eagerly as is the mind of the commander on the other side from the scientific general. Just what the respective enemies want and think, and what they know and do not know, are as hard thig for the teacher and the general to find out. Divination and perception, not psychological pedagogics or theoretical strategy, are the only helpers here. But, if the use of psychological principles thus be negative rather than positive, it does not follow that it may not be great use, all the same.