The encouragement of a lively play of the mind over experience, the stimulation of imagination or what Bertrand Russell calls "the joy of mental adventure" is thus one of the most important sources of art and science. The arousing of imagination depends primarily on the inherited curiosity of man which varies from the random and restless exploring of the child to the careful and persistent investigation of the trained scientist. The curiosity which prompts the child to experiment with objects in a hit-or-miss fashion is little more than the physiological overflow of action which has been noted above. Curiosity becomes more distinctively mental when it is social in character, when the child explores and experiments not by its own manipulations but by communication, by asking questions of other people. When the child learns that he can appeal to others to eke out his store of experiences, so that, if objects fail to respond interestingly to his experiments, he may call upon persons to provide interesting material, a new epoch sets in. "What is that?" "Why?" become the unfailing signs of a child's presence. At first this questioning is hardly more than a projection into social relations of the physical overflow which earlier kept the child pushing and pulling, opening and shutting. He asks in succession what holds up the house, what holds up the soil that holds the house, what holds up the earth that holds the soil; but his questions are not evidence of any genuine consciousness of rational connections. His _why_ is not a demand for scientific explanation; the motive behind it is simply eagerness for a larger acquaintance with the mysterious world in which he is placed. The search is not for a law or principle, but only for a bigger fact.... But in the feeling, however dim, that the facts which directly meet the sense are not the whole story, that there is more behind them and more to come from them, lies the germ of _intellectual_ curiosity.[1] [Footnote 1: Dewey: _loc. cit._, p. 32.]