The first two plates found rent in the cornfield — the differential of better land over worse, the no-rent margin that fixes the price. But the deepest lesson of the marginal land was that rent has, at bottom, nothing to do with soil. This plate states the general law toward which the first two were building all along: that rent is the surplus accruing to anything whose supply is fixed and cannot be made more of — land first, and most purely, but after land, every other thing that shares land's one defining trait, which is fixity. The plate sets the law out in its full generality, traces the spectrum of fixity from what is fixed forever to what is fixed only for the moment, and shows how the law turns the whole volume outward, from the single field toward every scarce position the later plates will visit. And it restates, in its most general form, the question on which the volume turns: that the surplus to a fixed thing is, by its very nature, a payment for nothing — and whether that makes it unearned is the matter of the rent.
The general law begins from a single question: what is it that sets rent apart from every other payment made in an economy? The answer is fixity. An ordinary price does work. The price of wheat calls forth wheat; the wage calls forth labour; the price of any made thing summons more of it into being. The price is the signal that elicits the supply, and earns its keep by doing so. But where the supply is fixed — where no rise in the price can call forth a single unit more — the price elicits nothing whatever; it merely hands a surplus to whoever owns the fixed thing. And this is the defining mark of rent: it is the part of a payment that is not necessary to bring the factor into being or to keep it in use, because the factor's supply does not depend upon the payment at all. The land lies there to be used at any rent, or at none; the whole of what it earns is therefore a surplus, paid over and above the nothing that would have sufficed to keep it in existence. Rent is the price that does no work — the payment that summons no supply.
Put into the language the modern science later gave it, the law turns on the elasticity of supply — on how readily the quantity of a thing answers to its price. At the one extreme stands a supply perfectly inelastic, fixed in quantity whatever the price, as the acreage of a county is fixed: there the entire return is rent, for the quantity stands unchanged at any price down to nothing, so that every penny paid is a surplus over that nothing, and the price is settled wholly by demand pressing against a quantity that will not yield. At the other extreme stands a supply perfectly elastic — a thing reproducible at constant cost — and there is no rent at all: any surplus above the cost would call forth more of the thing, and the new supply would compete the surplus away, until the price came to rest exactly at cost. And in the broad country between the two, where supply slopes upward, a part of the return is rent: the inframarginal units, supplied more cheaply than the last, each earn a surplus — the producer's surplus that is only rent under its general name. The more inelastic the supply, the larger the share of the return that is rent; and land, the most inelastic factor there is, is therefore the factor whose return is most nearly rent entire.
Rent is the price that summons no supply — what a thing commands for being fixed, and not for being made.
But fixity is a matter of degree, and of time — and this is the law's most fertile complication. Some things are fixed forever: the land, the unique site, the dead master's canvas. But far more things are fixed only for now — incapable of being multiplied quickly, though capable of it in time. A scarce skill is fixed until more people train to it; a building, until more are built; a machine, until more are made. And here is the crux: nearly everything is fixed in the short run and free to vary in the long. So in the short run, almost every return carries a rent — a surplus conferred by the fixity of the moment — while in the long run, as the supply catches up, that surplus erodes, and only the things fixed forever go on earning a rent that lasts. The rent on what is fixed only for a time has even earned its own name — the quasi-rent of the plate that follows — but it is the very same thing as rent, set apart only in that time dissolves it. Rent and quasi-rent are not two phenomena but one, strung out along the single axis of how long the fixity holds.
A refinement the law demands, lest it be mistaken. It is not scarcity as such that breeds rent, but scarcity that cannot be remedied by making more. A thing may be scarce and yet bear no rent, if its scarcity can be relieved: were diamonds scarce but freely got at constant cost, their price would settle at that cost, and no rent would cling to them. What generates rent is not that a thing is rare but that its supply cannot answer to its price — that the want of it cannot be made good by producing more. Where supply can respond, competition does its patient levelling, grinding every surplus down to nothing; where supply cannot respond, the surplus has nowhere to drain, and settles, permanently, as rent. This is why the law is a law of fixity and not merely of scarcity: the rent is the measure not of how scarce a thing is, but of how deaf its supply is to the price that its scarcity commands.
And now the law throws the whole volume open. For if rent is the return to fixity, then rent is to be found wherever anything is fixed — and the rest of these plates is little more than a tour of the kinds of fixity the world contains. There is the fixity of nature: the land, and the ores and oils the earth holds in a store it will not refill, whose rent a later plate must weigh. There is the fixity of place: the site near the centre, which none can shift or multiply, whose rent the plate on location will map across the city. There is the fixity of talent: the rare gift whose return the volume before already half-confessed to be a rent. And there is the fixity made not by nature but by law and by the architecture of markets: the patent, the licence, the parcel of spectrum, the monopoly, the platform's gate — scarcities conjured by decree or built up out of network, whose rents the volume's later plates will hunt to their several lairs. Land was only the first case, and the clearest.
Land was only the first case, and the clearest; the general law is that rent collects wherever supply is dammed — and the world is full of dams.
Two things must be said, though, before the law is let stand, lest it prove too sharp a blade. The first is that fixity is seldom absolute, and rarely innocent of its owner. Even land may be added to at the margin, by reclamation and by building upward, and worn away by neglect; and much of what passes for "fixed" is fixed only because someone laboured and spent to make it so — the skill that cost years to acquire, the patent that repaid a discovery, the network that took capital to build. The surplus to a fixed thing is not always the surplus to a gift of nature; sometimes it is the return upon the effort that produced the fixed thing, and to call that unearned is to mistake the rent for its cause. The second is that rent, even the purest rent upon the most fixed of factors, is not simply waste. A price that calls forth no new supply still does a necessary work: it rations the fixed thing to the use that values it most, so that the high rent of the prime site is exactly what ensures the site goes to its best use and not its second-best. Rent allocates even where it cannot elicit. The surplus to fixity wears two faces, then: it may be unearned, the bare toll of ownership; and it may be functional, the signal that steers a scarce fixed thing to its highest use — and most often, confoundingly, it is the two at once.
Return, then, with the general law in hand, to the question of the volume. Rent is the surplus that accrues to whatever is fixed and cannot be made more of — the price a thing commands not for being made but for being scarce beyond remedy. The law is perfectly general, and it is the key to all that follows: from land it reaches out to resource and site and talent and licence and gate, to every dam that holds supply back from the price that demand stands ready to pay. But the law, like the margin before it, frames the volume's question without ever closing it. That rent is a surplus over the supply price — a payment unneeded to call the fixed thing forth — is the strongest case there is for naming it unearned, the toll of mere possession; and it is the deep reason that rent can be taxed, as a later plate will show, without the fixed supply shrinking by a single acre. Yet the fixity may be the owner's own making, and the rent his return upon it; and even where it is not, the rent still does the work of steering the scarce thing to its best use. Whether the surplus to fixity is earned or extracted is, therefore, the same open question the whole volume turns upon — stated now in its most general form, and ready to be put, in the plates to come, to every fixed and unreproducible thing under the sun. As the table says of every price gathered within it, the argument remains open.