The Lighthouse

The pasture is a shared thing overused. Turn it inside out and you find its twin: a shared thing never made. The lighthouse on the dangerous coast would save ships and cargoes beyond counting; every captain who passed would gladly have its light. And yet, left to the market, the lighthouse may never be built at all — not because it is not worth its cost, but because no one can be made to pay for it.

The lighthouse is the textbook instance of a public good, and its defining properties are the mirror of the commons'. Its light is non-rival: that one ship steers by it takes nothing from the next, who steers by the same beam undimmed, so that serving an additional user costs nothing at all. And it is non-excludable: the light, once lit, shines on every hull in view, and no keeper can withhold it from the ship that has not paid. Paul Samuelson gave such goods their formal theory and drew the hard conclusion. Because the light cannot be withheld, no captain need buy it; he will be lit whether he pays or not. And because each captain reasons so, each waits for the others to fund the light, none pays, and the light — though its worth to all the ships together far exceeds its cost — is never built. The market, which supplies private goods so well, cannot supply this one, for it has no way to charge.¹

The disease has a name — the free-rider problem — and a depth worth plumbing. It is not merely that some dodge payment; it is that the rational course for each is to dodge, since the good comes free regardless, and so the very mechanism by which a market discovers what people want — their willingness to pay — fails here utterly. Ask the captains what the light is worth to them, meaning to charge each accordingly, and each, knowing his answer sets his bill but not his benefit, will understate: why confess a high value, and pay more, when the light will shine on me whatever I say? The market cannot learn the true demand for a public good, because the good's non-excludability makes honesty about its value a fool's move. The same structure as the commons returns, in mirror: there, each took more because the cost was shared; here, each gives less because the benefit is shared — and in both, the sharing severs private incentive from collective good.²

As with the pasture, so with the lighthouse: once the structure is seen, public goods are found to be the substance of much that markets cannot do and states are left to. National defense is a public good — it shields every citizen at once, and none can be left undefended for failing to pay, so it cannot be sold and must be taxed for. The clean air of a city, the control of a contagion, the basic research whose findings anyone may use, the law and order that protect all within a realm, the flood wall that guards a whole valley, the very knowledge of how the world works — each is non-rival, or non-excludable, or both, and each is therefore underprovided by a market that cannot charge for it. The list is long and weighty, and it explains a great deal: it is much of why states exist, and tax, and build what no merchant would. Where the commons is the tragedy of what markets overuse, the public good is the tragedy of what markets underbuild — and between them they mark out the broad territory the price cannot govern.³

Few goods are purely public, and the impure cases admit partial remedies worth marking, for they show the market straining against its limits. Some goods are non-rival but excludable — the bridge that costs nothing more for one more crossing, yet can be gated and tolled; the film any number may watch, yet only ticket-holders see; the patented idea, free to copy but fenced by law. These the volume calls club goods, and a market can supply them, though at a price above the zero that efficiency wants, since to charge anything for a thing that costs nothing to share is itself a kind of waste. And some public goods are funded by ingenuity: the lighthouse, famously, was sometimes paid for by levies on the ships in the nearby harbor, the one place the otherwise unchargeable beam could be tied to a gate. But these are workarounds at the margin; the central fact stands. Where a good cannot be withheld, the market cannot reliably price it, and what cannot be priced the market will not, of itself, provide.⁴

If the market cannot build the lighthouse, who shall? The same two answers offered for the commons present themselves here, in mirror. The state may build it and tax for it — compelling the payment that no captain would volunteer, and providing from public revenue what private revenue cannot raise; this is much of what public finance is. Or the beneficiaries might somehow bind themselves to provide it together — the harbor's merchants agreeing to a common levy, the villagers to a shared labor — supplying by collective agreement what neither market nor state imposed. The first is the Leviathan again; the second points, once more, toward the flagship's third way, the covenant of those who share a need. For the public good and the commons, being one problem in mirror, have the same three possible answers — the market that fails, the state that commands, and the community that binds itself — and the volume's argument is the slow turn from the first, through the second, to the third.⁵

The lighthouse is the commons inverted: not a shared thing taken to ruin, but a shared thing never raised, starved by the same severance of private incentive from common good that overgrazed the pasture — there a cost shared and so ignored, here a benefit shared and so unfunded. With the tragedy and its mirror both before us — overuse and underprovision, the commons depleted and the public good unbuilt — the volume can turn to the logic that underlies them both, and that reaches far beyond fisheries and lighthouses into every effort of a group to serve its common interest. The next plate takes up collective action itself, and the hard law that governs it: that the more who share a goal, the less, often, any one of them will do to reach it.