But after all has been said on the head of conservation of the good old ways, it remains true that institutions change and develop. There is a cumulative growth of customs and habits of thought; a selective adaptation of conventions and methods of life. Something is to be said of the office of the leisure class in guiding this growth as well as in retarding it; but little can be said here of its relation to institutional growth except as it touches the institutions that are primarily and immediately of an economic character. These institutions--the economic structure--may be roughly distinguished into two classes or categories, according as they serve one or the other of two divergent purposes of economic life. To adapt the classical terminology, they are institutions of acquisition or of production; or to revert to terms already employed in a different connection in earlier chapters, they are pecuniary or industrial institutions; or in still other terms, they are institutions serving either the invidious or the non-invidious economic interest. The former category have to do with "business," the latter with industry, taking the latter word in the mechanical sense. The latter class are not often recognized as institutions, in great part because they do not immediately concern the ruling class, and are, therefore, seldom the subject of legislation or of deliberate convention. When they do receive attention they are commonly approached from the pecuniary or business side; that being the side or phase of economic life that chiefly occupies men's deliberations in our time, especially the deliberations of the upper classes. These classes have little else than a business interest in things economic, and on them at the same time it is chiefly incumbent to deliberate upon the community's affairs.