In general no-rent land is commonly utilized in an extensive way and very good land in an intensive way; and in stating the old formula for rent we need to be careful to make it mean that the rent of the good piece is its total product less the product that can be had by taking from the good piece the labor and capital it now absorbs and setting them at work on a piece of the poorest land which is enough larger than the good one to enable us to secure a crop which will be worth just the amount of wages and interest we must pay. The larger size of the poor piece of land is an essential condition. _Real Significance of Rent Formula._--It will be seen that this formula amounts to saying that the rent of land is what the land itself adds to the marginal product of labor and capital. Put a certain amount of labor and capital on a piece of land of good quality, and you get a certain amount of product. Withdraw the land from the combination, and you force the labor and capital to become marginal increments of these agents. They must go elsewhere and get what they can. One alternative that is open to them is that of seeking out land of a grade so poor that it has not been previously utilized and doing what they can to get a product out of it. Whatever they can make such land yield is, in an economic sense, wholly their own product. There is an indefinite quantity of this kind of land to be had, and wherever labor and capital utilize any part of it, they can have all that they produce. Now if we subtract what they there create from what was created when they were working on the good land, we have the rent of that land.