But the approach from the side of income has been shown to be in some important cases the historical origin of the rate of interest, and we need but reconsider reasoning that has gone before to see that this is the logical order in all cases. Rent, or income, is a link in the chain of value, connecting gratification or psychic income, consumption goods, rent or usufruct value, and finally capital value. To one keeping in mind the logical cause of value, it becomes inconceivable that capital value could precede income, a view possible only when a fragment of the problem is seen. This being true, the mere mention of a capital sum implies the interest problem, and assumes the interest rate. The capital is of that amount because the anticipated incomes, discounted at some rate, equal that sum. The capital sum is a certain number of years' purchase of the series of rents which can be secured by the use of wealth in various industries. The owner of a number of dollars (or of an amount of other wealth expressed in dollars) has open to him various investments. The value of any wealth is due to the possibility of deriving incomes from it. If, however, the expected income fails to be realized, the capital loses its value, or it is revalued on the basis of the new rents. The investment is then said to be a losing one. Thus, at each stage in the valuation of capital, before it is invested and at every moment thereafter when the valuation is readjusted to the rents realized or expected, rents are logically primary, the source from which the capital sum is derived. [Sidenote: The rate of capitalization of rents is not fixed merely in commerce] 3. _The capitalization of comparatively safe permanent incomes from real estate contains within itself all the factors for the independent determination of the interest rate, and is not to be explained merely by reference to "the prevailing rate of interest" in other investments._ The value of land usually is explained simply as the capitalizing of its rents at "the prevailing rate of interest." The rate is assumed to be fixed by conditions in manufacturing and commerce, and if five per cent, can be gotten there the capitalist would never buy land unless investment in it were made equally attractive. The cause of the rate thus is supposed to rest outside the transaction itself, the exchange of land for other capital seeking investment. The economic student is safe in assuming always that explanations of this sort are fallacious. The cause of value in any one exchange or any one industry is not thus to be juggled and shifted into another industry. It is true that the values of goods are so wonderfully interrelated by substitution that as the price of fresh beef will affect that of salt mackerel, so the capitalization rate of machinery affects that of land; but the influence is not from one side only, it is mutual. When anything has value, it must have in itself an independent cause of value.