xv CONCEPTUAL THOUGHT 357 



upon the plasticity of those who learn by it. In short, at 

 this stage, we have organised racial experience largely 

 taking the place of that hereditary structure which 

 represents the result of an infinity of conflicting and 

 chaotic experiences in past generations. In fine, in the 

 highest animal species, instinct lays the ground plan of 

 conduct, within which details may be remodelled by 

 individual experience. In the human species, the ground 

 plan is itself reconstituted by the organised experience 

 of the race. 



9. To bring together the main heads of our account, 

 we have suggested that human intelligence develops out of 

 a lower form by growth in those features of Comprehen- 

 sion on the one hand, and Articulateness on the other, by 

 which the higher stage of animal intelligence was marked 

 out from the lower, (a) Mind, it is suggested, differs 

 from mind in the degree in which these powers are 

 developed, in the area of experience which it can com- 

 prehend, and in the articulateness with which it' can 

 comprehend it. But here, as elsewhere, there come points 

 in growth where change of degree becomes change of 

 kind. The constitution of a physical body is understood 

 to be determined by the energy of movement on the part 

 of its constituent molecules. Increase the vibration of the 

 constituent molecules, and a solid body gets warmer to the 

 touch, and expands in volume. Increase it still further, 

 and other physical characteristics are changed. The body 

 perhaps becomes soft and pliable. Presently there comes 

 a point at which the solid body becomes liquid, the energy 

 of movement having overcome the forces which cause 

 each swinging molecule to return constantly to the same 

 point. Increase it yet again, and the liquid becomes a 

 vapour, the energy of movement having altogether over- 

 come that of cohesion. Thus do successive increments of 

 quantity, as they pass certain critical phases, produce 

 changes of quality. In the instance just taken, the 

 change of quality is, as I understand, due to the disturb- 

 ance of the relation between the force that is increasing 

 and the force that remains constant. In the mental 

 world, the change may be explained in this way : that 



