The primary business of a teacher is to teach. But everyone who has had practical experience of teaching has found that he has learned from his pupils almost as much as he has taught, since contact with younger minds supplies a new point of view, which imparts a fresh novelty to familiar facts. For example, when a man is acquiring a living language, he learns the pronunciation (not only syllabic pronunciation but the significant tones and inflexions of the language) by sheer imitation, by trusting to his aural memory and his power of grasping sounds unfamiliar to him in his own tongue. But when he tries to impart his accomplishment to others, he must needs analyse, if he is to explain, what he has learnt. Hence teaching, if it is not mere mechanical transmission of information, such as can be got from a book, becomes, in effect, a species of research.