The rent tells us that access is valuable; it does not yet tell us why access is scarce. A field beside the market cannot be moved to make room for a second identical field. A workshop can sometimes be copied, but its rivals may be forbidden to open. The two situations can leave a similar surplus in the owner's account while presenting different questions to everyone outside the gate. One asks how a limited resource should be allocated and how its proceeds should be shared. The other asks why an alternative that could be supplied has been withheld. This distinction lies beneath the volume's movement from Ricardo's land to the protected position. It is also the distinction the language of scarcity can conceal. To call something scarce is to describe a relation between what people want and what they can obtain. The next question concerns the process that fixes what they can obtain: nature, time, cost, a rule, a strategy, or some combination of them. The rent acquires its character from that history of the limit.
Natural scarcity can yield a rent even when the owners compete and use their resources fully. Marshall makes the point with an imagined stock of exceptionally hard stones, capable of valuable work and impossible to increase. Suppose every stone is worked as far as it is worth working, with additional uses pursued until their product just covers the additional expense. The stones can still earn a surplus because their services are wanted and their total supply is limited. No agreement to hold them idle is needed. The advantage may be measured against a less productive use of the same stones, or against the services available from an inferior substitute. Scarcity rent and differential rent are therefore connected ways of reading the return. The rent need not wait for an inferior field to appear on the map; an intensive margin can perform the same analytical work. What matters is the relation between the stock, its possible uses, and demand. Removing a particular owner changes who receives the surplus, but leaves a further question about how access to the limited services will be decided.1
The fixed total must also be distinguished from the quantity available to a particular use. A parcel can be physically present regardless of its rent while still being withheld from farming because another activity can pay more for it. A machine already made can move between products; a worker with a rare capacity can choose among occupations. The opportunity sacrificed by bringing the resource into this use belongs in the comparison, even when no payment can make another identical resource exist. This is why the supply response depends on the question's boundary. The whole stock may be fixed while supply to a trade is responsive. A rent payment can help ration access among competing users without calling a new unit into being. The ownership of the resulting surplus and the usefulness of that rationing are separate matters. Neither the observation that the stock is fixed nor the observation that the payment allocates it settles how the income should be distributed. The preceding plate on The Excess supplies the necessary discipline: name the alternative before deciding which part of the payment exceeds what was needed to retain the resource here.2
Deliberate restriction changes the comparison because additional valuable service could have been supplied. Take a simple market in which demand is price = 120 − quantity, production costs 20 for each unit, and there are no fixed costs or other effects on society. Competitive supply at a price of 20 serves one hundred units. A single-price seller controlling the whole supply instead maximizes its profit by selling fifty units at 70. It earns 2,500, while fifty units that buyers value above their cost are left unmade. The lost gains from those trades total 1,250 in this illustration. The owner's income and the loss are different quantities: some of the change transfers purchasing power from buyers to the seller, while some destroys gains neither side receives. The contrast with Marshall's fully used stones is exact under the stated assumptions. The resource limit in the first case constrains what can be supplied; the seller in this case chooses to supply less than the available technology would make worthwhile for buyers and producers together.3
The source of the seller's control is therefore part of the welfare inquiry, not a decorative label added after it. An exclusive permission can keep otherwise capable rivals out; a coordinated refusal to expand can preserve a shortage. But production itself can also make a single supplier cheaper than several separate systems, as when a network requires a large common installation. Marshall's monopoly chapter expressly warns that the cost schedule under divided production may differ from the monopolist's schedule. Comparing the two arrangements while pretending their costs are identical can miss the economy of operating at scale. The saving does not settle what price the supplier should charge or who should receive its benefit. It identifies a real service that must be included when choosing among institutions. The same discipline applies to created capacity: a temporary return may be part of the inducement to invest, as the plate on quasi-rent showed. A defended position can combine that return with an additional advantage from excluding alternatives. The inquiry must follow both parts rather than assume that the existence of a barrier alone proves the whole payment necessary or the whole payment wasteful.4
A fishery makes the distinction unusually sharp because unrestricted access can itself waste the scarce resource's value. In H. Scott Gordon's 1954 model, entry and fishing effort can dissipate the rent as each fisher pursues a private return without controlling the stock. Coordinated effort can preserve a surplus by reducing the cost of obtaining the catch. In the single-ground case he analyzes without product-price effects, this gain comes from better use of the resource, rather than from raising the market price through a manufactured shortage. The design still matters: a total-catch limit can leave a costly race to catch the permitted fish before others do. The presence of a limit therefore tells us too little. We must ask what behavior it changes and whether it protects the resource or merely protects its holders. Even when a rule improves the use of the fishery, the allocation of the resulting claims remains a further distributive choice.5
The distinction between found and manufactured scarcity survives these complications by becoming a question one can actually investigate. What could be supplied if the disputed restriction were removed? Which costs would change, which investments would still be made, and which effects on others would cease to be ignored? Who would gain access, and who would lose the income attached to the existing rule? The answers identify the surplus before the argument over its rightful destination begins. A naturally scarce position can carry a claim created by law; an imposed limit can protect something real; an efficient arrangement can still distribute its benefits narrowly. The volume's suspicion is strongest when an exclusion sacrifices valuable alternatives chiefly to preserve the holder's return, and strongest because the alternatives can be named. The next plate follows such positions into the network, the patent, the brand, and the gate. It asks how much income comes from making what people need, and how much from controlling the place through which they must pass to obtain it.