ABSTRACT
This chapter discusses the problem of the sources of the material force notion in the mind of the child. The most general characteristic of the primitive explanations of movement given by children is what may be called their bipolarity: the movement of a body is regarded as due both to an external will and to an internal will, to a command and an acquiescence. Even during the stage when the child is trying to explain the movements of nature by nature herself, every movement is still explained by the cooperation of external and internal motor force. Since the idea of force or strength plays so important a part in forming the child's picture of the world, it may be of interest to enquire how children define it. The fact that the idea of force owes its existence to inner experience seems to be beyond dispute.
