Now, as to what these conditions and forces are, there is a familiar answer ready for us—◆¹ Land, Labour, and Capital; and, with a certain reservation, we may take this to be true. But as Capital is itself the result of Land and Labour, we need not, for the moment, treat Capital separately; but we may say that the heap is produced by Land and Labour simply. I use this formula, however, only for the purpose of amending it. It will be better, for reasons with which I shall deal presently, instead of the term Labour to use the term Human Exertion. And further, we must remember this—the heap of commodities we have in view is no mere abstraction, but represents the income of this country at some definite date; so that when we are talking of the forces and conditions that have produced it, we mean not only Human Exertion and Land, but Human Exertion of a certain definite amount applied to Land of a definite extent and quality. [Sidenote ◆1 The first point we notice is that the exertion of the same number of men applied to the same land does not always produce the same amount of wealth.] [Sidenote ◆2 This must be due to some varying element in the Human Exertion in question.] [Sidenote ◆3 Let us compare production in this country 100 years ago with production now.] ◆¹ Now, as I pointed out in the last Book, one of the most remarkable things about our national production of commodities, is that the yearly exertion of the same number of men, applied to land of the same extent and quality, has been far from producing always a heap of the same size. On the contrary, the heap which it produces to-day is twice as large as that which it produced in the days of our fathers; and nearly three times as large as that which it produced in the days of our grandfathers. Here then is the reason why the inquiry that is before us is twofold. For we have at first to take some one of such heaps singly—on several accounts it will be convenient to take the smallest, namely that produced about a hundred years ago—and to analyse the parts which Land and Human Exertion played respectively in the production of _it_. Then, having seen how Land and Human Exertion produced in the days of our grandfathers a heap of this special size, we must proceed to inquire why three generations later the same land and the exertions of a similar number of men produce a heap which is nearly three times as large. For the difference of result cannot be due to nothing. ◆² It must be due to some difference in one of the two causes—to the presence in this cause of some varying element: and it is precisely here—here in this varying element—that the main interest of our inquiry centres. For if it is owing to a variation in this element that our productive powers have nearly trebled themselves in the course of three generations, nearly two-thirds of the income which the nation