=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. DANGERS OF OMITTING EXPRESSION =A. Knowledge not Practical.=--It is apparent, then, that if the pupil is not given opportunity for expression, his ideas are vague and evanescent. Further than this, his capacities for _knowing_ will be developed but his capacities for _doing_ ignored. His _intellectual_ powers will be exercised and his _volitional_ powers neglected. The pupil is thus likely to develop into a mere _theorist_; and as the tendencies of childhood are accentuated in later life, he becomes an _impractical_ man. There are many men in the world who apparently know a great deal, but who, through inability to make practical application of their knowledge, are unsuccessful in life. It is, however, seriously to be doubted whether knowledge is ever _real_ until it has been worked out in practice and conduct. To avoid the danger of becoming impractical, a pupil should have every opportunity for expression.