=6. Use of Knowledge as Motive.=--In the preceding cases, interest in the problem is made to rest primarily upon some native instinct, or tendency. It is to be noted, however, that as the child advances in the acquisition of knowledge, or experience, there develops in him also a desire for mental activity. In other words, the normal child takes a delight in the use of any knowledge over which he possesses adequate control. It is to be noted further, that the child masters the new problem by bringing to bear upon it suitable ideas selected out of his previously acquired experiences. It is evident, therefore, that, when a lesson problem is presented to the child in such a way that he sees a connection between it and his present knowledge and feels, further, that the problem may be mastered by a use of knowledge over which he has complete mastery, he will take a deeper interest in the learning process. When, on the other hand, he has imperfect control over the old knowledge from which the interpreting ideas are selected, his interest in the problem itself will be greatly reduced. Owing to this fact, the teacher may adapt his lesson problems, or motives, to the stage of development of the pupils. In the case of young children, since they have little knowledge, but possess a number of instinctive tendencies, the lesson problem should be such as may be associated with their instinctive tendencies. Since, however, the expressing of these tendencies necessarily brings to the child ideas, or increases his knowledge, the pupil will in time desire to use his growing knowledge for its own sake. Here the child becomes able to grasp a problem consciously, or in idea, and, so far as it appeals to his past experience, will desire to work for its solution. Thus any problem which is recognized as having a vital connection with his own experience constitutes for the child a strong motive. For older pupils, therefore, the lesson problem which constitutes the strongest motive is the one that is consciously recognized and felt to have some direct connection with their present knowledge. KNOWLEDGE OF PROBLEM