Such a contract differed not in economic purpose, but only in form and terms of obligation, from the renting of wealth. The church writers, however, got much confused in regard to the nature of money loans. They did not see that it was _things_ which the merchant wished to borrow. They did not see that the money loan was simply a more convenient mode of transferring the use of wealth from one person to another. The moralists and lawmakers of that day said: Money is unfruitful, therefore taking interest for it is robbery. We cannot follow here the controversy as to the justice of interest on money which involved other ideas than those mentioned, but even to the present time traces of the old fallacy may be seen more or less plainly in the economic theory as well of conservative writers as of the socialistic opponents of interest. The principal sum expressed in the loan contract was called the capital sum, from _caput_, head, and the amount paid for its use was first called usury, money for the use. How the word interest came to take its place, and the word usury came to mean _excessive_ interest is one of the most interesting chapters in economic history. The term capital then came to be connected with city wealth, with movable forms of wealth, with things supposed to be peculiarly "the product of labor"; and interest was assumed to be connected only with this capital. The term rent on the other hand was connected especially with the use of land. The connection was a historical accident, but it has had an important influence on economic theory. [Sidenote: Rivalry of the commercial and landholding classes in Europe] 6. _The owners of city wealth and of country landed estates often were opposed as well in social and political as in economic affairs._ The practical economic questions of the Middle Ages and the practical political questions largely turned on these two groups of interests. The men of wealth in the cities, the merchants and manufacturers, often were found opposed to the landed aristocracy. This social division between the commercial and agricultural classes doubtless helped to strengthen the prejudgment as to the nature of the two kinds of wealth. Indeed, in view of the situation, it may have been in a measure justifiable and expedient to contrast the thought of city wealth, which has come to be called capital, with that of landed wealth. But even if it were, it is now misleading and erroneous to continue the use of such concepts in a new country and in our modern conditions. [Sidenote: Land continues to be rented while city wealth is borrowed in money form]