To understand this, the reader need only reflect on those three principal and familiar parts into which the annual income of every civilised nation is divided, not only in actual practice, but theoretically by Mill himself—namely Rent, Interest, and Wages.[26] For these—what are they? The answer is very simple. They are portions of the income which correspond, at all events in theory, to the amounts produced respectively by Land, Capital, and Human Exertion; and which are on that account distributed amongst three sets of men—those who own the Land, those who own the Capital, and those who have contributed the Exertion. There are many causes which in practice may prevent the correspondence being complete; but that the general way in which the income is actually distributed is based on the amount produced by these three things respectively,—Land, Capital, and Human Exertion,—is a fact which no one can doubt who has once taken the trouble to consider it. It is thus perfectly clear that, contrary to what Mill says, though two or more agencies may be equally indispensable to the production of any wealth at all, it is not only not “unmeaning to say that so much is produced by one and so much by the other,” but it is possible to make the calculation with practical certainty and precision; and I will now proceed to explain the principles on which it is made. CHAPTER II _How the Product of Land is to be distinguished from the Product of Human Exertion._ The question before us will be most easily understood if we begin with once again waiving any consideration of Capital, and if we deal only with what Mill, in the passage just quoted, calls “Nature and Labour”—or, in other words, with Land and Human Exertion. We will also, for simplicity’s sake, confine ourselves to one use of land—its primary and most important use, namely its use in agriculture or food-production. [Sidenote ◆1 Rent is the proportion of the produce produced not by Human Exertion, but by the Land itself;]