(b) While direct impression has the advantage of being first hand, it also has the disadvantage of being limited in range. Direct acquaintance with the natural surroundings of the home environment so as to give reality to ideas about portions of the earth beyond the reach of the senses, and as a means of arousing intellectual curiosity, is one thing. As an end-all and be-all of geographical knowledge it is fatally restricted. In precisely analogous fashion, beans, shoe pegs, and counters may be helpful aids to a realization of numerical relations, but when employed except as aids to thought--the apprehension of meaning--they become an obstacle to the growth of arithmetical understanding. They arrest growth on a low plane, the plane of specific physical symbols. Just as the race developed especial symbols as tools of calculation and mathematical reasonings, because the use of the fingers as numerical symbols got in the way, so the individual must progress from concrete to abstract symbols--that is, symbols whose meaning is realized only through conceptual thinking. And undue absorption at the outset in the physical object of sense hampers this growth. (c) A thoroughly false psychology of mental development underlay sensationalistic empiricism. Experience is in truth a matter of activities, instinctive and impulsive, in their interactions with things. What even an infant "experiences" is not a passively received quality impressed by an object, but the effect which some activity of handling, throwing, pounding, tearing, etc., has upon an object, and the consequent effect of the object upon the direction of activities. (See ante, p. 140.) Fundamentally (as we shall see in more detail), the ancient notion of experience as a practical matter is truer to fact that the modern notion of it as a mode of knowing by means of sensations. The neglect of the deep-seated active and motor factors of experience is a fatal defect of the traditional empirical philosophy. Nothing is more uninteresting and mechanical than a scheme of object lessons which ignores and as far as may be excludes the natural tendency to learn about the qualities of objects by the uses to which they are put through trying to do something with them.