According to ancient prescription, then, all normal, legitimate economic activities carried on in a well regulated community serve a materially useful end, and so far as they are lucrative they are so by virtue of and in proportion to a productive effect imputed to them. But in the situation as it exists at any time there are activities and classes of persons which are indispensable to the community, or which are at least unavoidably present in modern economic life, and which draw some income from the aggregate product, at the same time that these activities are not patently productive of goods and can not well be classed as industrial, in any but a highly sophisticated sense. Some of these activities, which are concerned with economic matters but are not patently of an industrial character, are integral features of modern economic life, and must therefore be classed as normal; for the existing situation, apart from a few minor discrepancies, is particularly normal in the apprehension of present-day economists. Now, the law of economic equivalence and equity says that those who normally receive in income must perforce serve some productive end; and, since the existing organization of society is conceived to be eminently normal, it becomes imperative to find some ground on which to impute industrial productivity to those classes and employments which do not at first view appear to be industrial at all. Hence there is commonly visible in the classical political economy, ancient and modern, a strong inclination to make the schedule of industrially productive employments very comprehensive; so that a good deal of ingenuity has been spent in economically justifying their presence by specifying the productive effect of such non-industrial factors as the courts, the army, the police, the clergy, the schoolmaster, the physician, the opera singer. But these non-economic employments are not so much to the point in the present inquiry; the point being employments which are unmistakably economic, but not industrial in the naive sense of the word industry, and which yield an income.