=A. Influences Conduct.=--In nature study, history, and literature, the most valuable kind of expression is that which comes through some modification of future conduct. That pupil has studied the birds and animals to little purpose who needlessly destroys their lives or causes them pain. He has studied the reign of King John to little purpose if he is not more considerate of the rights of others on the playground. He has gained little from the life of Robert Bruce, Columbus, or La Salle, if he does not manfully attack difficulties again and again until he has overcome them. He has not read _The Heroine of Verchères_, or _The Little Hero of Haarlem_ aright, if he does not act promptly in a situation demanding courage. He has learned little from the story of Damon and Pythias if he is not true to his friends under trying circumstances, and he has not imbibed the spirit of _The Christmas Carol_ if he is not sympathetic and kindly toward those less fortunate than himself. From the standpoint of the moral life, therefore, right knowledge is valuable only as it expresses itself in right action.
=B. Aids Impression.=--Apart from the fact that it satisfies a demand of our being, expression is most important in that it tests the clearness of the applied knowledge. We often think that our impression is clear, only to discover its vagueness when we attempt to express it in some form. People often say that they understand a fact thoroughly, but they cannot exactly express it. Such a statement is usually incorrect. If the impression were clear, the expression under ordinary circumstances would also be clear. In this connection a danger should be pointed out. Pupils sometimes express themselves in language with apparent clearness, when in reality they are merely repeating words that they have memorized and that are quite meaningless to them. The alert teacher can, however, by judicious questioning, avoid being deceived in this regard.
=C. Adds to Clearness of Knowledge.=--Not only does expression test the clearness of the apperceived new knowledge, but at the same time it gives the knowledge greater clearness. We learn to know by doing. A pupil realizes a story more fully when he has reproduced it for somebody else. He images a scene described in a poem more clearly when he has drawn it. He has a clearer idea of the volume of a cord when he has actually measured out a cord of wood. He has a more accurate conception of the difficulties attending the discoveries of La Salle when he has drawn a map and traced the routes of his various expeditions. There is much truth in the statement that one never fully knows some things until he has taught them to somebody else. The teacher in grammar and geography will often have occasion to realize this. Greater clearness of impression means, of course, greater permanence. We remember best those facts of which our impression was most vivid.