§4. Naïve Productivity Explanations

One of the most common superficialities in this field of thought is the naïve idea that interest expresses the physical productivity of land, or of nature, or of man. When the rate of interest is 5 per cent, nothing at first thought seems more plausible than that this rate obtains because capital goods will yield 5 per cent in kind. It is alleged that because fruit trees bear apples or peaches, and because a bushel of wheat sown has the power to multiply into 50 bushels, and because a herd of cattle Edition: current; Page: [54] if unmolested may double in numbers every two years interest is therefore inherent in nature. As a matter of fact, this productivity, as we shall see, is a real element in the explanation of interest; but it is not the only one nor is it as simple as it seems.

In some degree, the theory elaborated in this book is a productivity theory. I am, therefore, not attempting to refute all productivity theories indiscriminately but merely to show the inadequacy of what Böhm-Bawerk called the "naïve" productivity theory. This theory, or fallacy, is not espoused by any careful student of the interest problem, but it exists in the minds of many before they begin to analyse the problem. It confuses physical productivity26 with value return.

Following the principles of Chapter I, we may take, as an illustration, an orchard of ten acres yielding 1000 barrels of apples a year. The physical productivity, 100 barrels per acre per year, does not of itself give any clue to what rate of return on its value the orchard yields. To obtain the value return on the orchard, we must reduce both physical income and capital goods (the farm) to a common standard of value. If the net annual crop of apples is worth $5000 and the orchard is worth $100,000, the ratio of the former to the latter, or 5 per cent, is a rate of value return; and if this rate is maintained without depreciation of the value of the orchard, this rate of value return is also the rate of interest. But how can we thus pass from heterogeneous quantities to homogeneous values? How can we translate the ten acres of orchard and the 1000 barrels of apples into a common standard—dollars? May not this apparently simple step beg the whole question? The important fact, and the one lost Edition: current; Page: [55] sight of in the naïve productivity fallacy, is that the value of the orchard is not independent of the value of its crops; and, in this dependence, lurks implicitly the rate of interest itself.

The statement that "capital produces income" is true only in the physical sense; it is not true in the value sense. That is to say, capital value does not produce income value. On the contrary, income value produces capital value. It is not because the orchard is worth $100,000 that the annual crop will be worth $5000, but it is because the annual crop is worth $5000 net that the orchard will be worth $100,000, if the rate of interest is 5 per cent. The $100,000 is the discounted value of the expected income of $5000 net per annum; and in the process of discounting, a rate of interest of 5 per cent is already implied. In general, it is not because a man has $100,000 worth of property that he will get $5000 a year, but it is because he will get that $5000 a year that his property is worth $100,000—if the pre-existing rate of interest remains unchanged.

In short, we are forced back to the confession that when we are dealing with the values of capital and income, their causal connection is the reverse of that which holds true when we are dealing with their quantities. The orchard is the source of the apples; but the value of the apples is the source of the value of the orchard. In the same way, a dwelling is the source of the shelter it yields; but the value of that shelter is the source of the value of the dwelling. In the same way a machine, a factory, or any other species of capital instrument is the source of the services it renders but the value of these services is the source of the value of the instrument which renders them.

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This principle is complicated, but not impaired, by the fact that the cost of production of further dwellings, machines, tools, and other capital plays a part. The principle which rests on future incomes, including, of course, items of negative future income (costs) applies to any existing capital at any stage of its existence. The value of anything (as indicated in Chapter I, and more fully in The Nature of Capital and Income) is typified by the case of a bond whose value, as every broker knows, is calculated solely from the future services, or sums, expected and the rate of interest and the risk. The cost of producing other competing houses or other instruments so valued, in so far as that cost lies in the future, has an important influence. Past costs may also affect the value of the house by influencing through competition the value of the future services or disservices of that house, or the rate of interest, or the risk. Thus, cost plays an important rôle but not the simple one usually assumed.

Although business men are constantly employing this discounting process in the valuation of every specific item of property bought or sold, they often cherish the illusion that somehow, somewhere, there is capital which does not get its value by discounting future services but has already made value which produces interest. They persist in thinking of interest as moving forward in time instead of as discount moving backward.

The necessity of presupposing a rate of interest is re-inforced by observing the effect of a change of the rate of productivity. If an orchard could in some sudden and wholly unexpected way be made to yield double its original crop per acre, only its yield in the sense of physical productivity would be doubled; its yield in the sense of the rate of interest would not necessarily be affected at Edition: current; Page: [57] all, certainly not doubled,27 because the value of the orchard would automatically advance with an increase in its value productivity.

The rate of physical productivity is evidently not the rate of interest. The rate of physical productivity is not ordinarily even the same kind of magnitude as the rate of interest. Bushels of wheat produced per acre is an entirely different sort of ratio from the rate per cent of the net value of the yield of land relative to the value of the land. Interest is a rate per cent, an abstract number. Physical productivity is a rate of one concrete thing relatively to another concrete thing incommensurable with the first.