The term "interest," first applied in the Middle Ages to a payment for the use of a money loan, came to be used more broadly by the earlier economists as the income attributable to those goods which generally were bought and sold in terms of money. In other words, interest was supposed (though erroneously) to be uniquely connected with the particular production instruments to which the term capital was narrowly and mistakenly confined. Still more to add to the confusion, the term interest was about this same time identified with the broad problem of time-value. The terminology has remained ever since in this stage of arrested development. Our suggestion is to retain the word interest in its original meaning, still almost universal in business circles, of a contractual payment on money loans, applying the term time-value (for lack of a better word) to the subtler economic problem. [Sidenote: Rent and time-value are essentially different phrases of the value problem] Time-value is here understood to be that all-pervading difference in the values of uses and gratifications of wealth at different points of time. A comparison of the value of momently appearing uses of wealth is the rent problem. Here are, therefore, very different aspects of the value problem. The rent conception is earlier grasped by men, is nearer in point of logic; the concept of time-value has only recently been clearly recognized. If men lived only in the moment, they would be concerned only with rent; living in the future also, they are constantly regulating their acts with reference to time-value. CHAPTER 18 RELATIVELY FIXED AND RELATIVELY INCREASABLE FORMS OF CAPITAL § I. HOW VARIOUS FORMS OF CAPITAL MAY BE INCREASED [Sidenote: The older and the modern way of viewing wealth]