The stability of language is another phenomenon of the same kind. The fundamental phonetic characteristics of a language are based on motor habits; the use of vocabulary and of grammatical forms partly on auditory associations. In all these cases; in the use of tools, forms and language the mind becomes so thoroughly adjusted to the use of definite motor habits, and to certain types of association between sense impressions and definite activities, that a resistance to change appears as the most natural mental attitude; if for no other reason, because it requires the effort of unlearning and relearning. It must be understood that this does not imply an absolute stability, which does not exist, but merely the individual resistance to sudden changes. In another way this resistance is expressed through an emotional attachment to customary forms. In the domain of tools it is perhaps not so much the pleasure of play that induces man to bestow much labor upon the manufacture of his utensils, as rather the love of the special tool that he is using, a love that implies pleasure in the customary movements as well as in the form of the implement. This mental attitude is one of the most important sources of the conservatism in the form of objects of use, and of the tendency to give to them the greatest possible technical excellence. The intensity of the emotional relation between a person and his tool is naturally greatest when maker and user are the same person; it must decay with the ease with which substitutes are obtained. Here is one of the causes of the rapid decay in the beauty of form of native utensils as soon as European tools and manufactures are introduced.