1. _The buying of any indirect agent is practically the purchasing of a "rent-charge."_ To account rationally for the market value of anything, its importance must be traced back to "gratification." We have examined and accepted the proposition that if a good is not affording enjoyment at the present moment it is kept because it will yield a rent until it is used. If it is never to afford direct enjoyment, if it is never to mature physically into the class of enjoyable goods, the explanation for its value must be found in the fact that it is capable of yielding a series of rents of enjoyable goods. In the last analysis the value of anything must be found in its power of affording psychic income, a series of psychic rents. Now when such a durable income is bought outright, what is the basis on which its value is estimated? What other than the rents it will afford? Exactly as did the purchasers of a medieval rent-charge, the buyer of the durable wealth pays a definite sum in return for the right to enjoy a series of future rents. As was the case with rent-charges, however, the amount paid will be less than the full matured value of the rents. A long series, even a perpetual series, may be exchanged for no more than ten, twenty, or twenty-five annual rents. While therefore the selling value of the good is the sum of the values of the rents, it evidently is that sum discounted. Immediately, when we have reached this point in the reasoning, our proposition must suggest itself as self-evidently true in this form: the value of any good is the sum of the entire series of rents it contains, discounted, at _some_ rate, to their present worth. What determines the rate of discount is a question that will call later for a fuller explanation. [Sidenote: Capital value is not primary] 2. _There are two modes of approach to the problem of interest: one from the side of income (rents); the other, from the side of the bearer (capital)._ The rate of interest expresses a relation between two values, the value of the income and the value of the sum loaned, whether it consists of money or of other wealth expressed in terms of money; But which of these values is primary in a study of the causes of value? Which is the base from which the other is derived by multiplying at the rate expressing their ratio? The answer to this question cannot be a matter of indifference to the economic theorist. Universally heretofore the study of interest has been approached from the side of capital. A capital sum was said to be invested and to earn a certain interest, that is, per cent., of that sum. The usage of speaking of the investment of capital as a sum given, and of "interest on capital" predisposes the mind to this view. [Sidenote: Expected rents are primary, and capital value is the "years' purchase"]