The first modern stock market opened in Amsterdam in 1602, when the Dutch East India Company issued shares a holder could sell on to someone else. For the first time you could own a piece of an enterprise in the morning and be rid of it by the afternoon. That convenience carried a dependency inside it that has never gone away, and that every market since has had to manage: to sell, you need someone willing to buy. Liquidity is not a property of the thing you hold. It is a property of whoever is standing across from you when you decide to leave.

For four centuries the party standing across from you was a person. The Amsterdam bourse had its jobbers, the London exchange its stockjobbers, and the New York Stock Exchange its specialists – a dealer assigned to each listed stock and obligated, in the exchange's own words, to maintain a "fair and orderly market." The specialist quoted a price to buy and a price to sell from his own account and stepped in to absorb the difference when buyers briefly outnumbered sellers or the reverse. He was the market's standing counterparty: the party who was always supposed to be there, so that an ordinary holder never had to go hunting for a bid.

The flaw in a counterparty made of people is that people have discretion, and discretion sprints for the door at exactly the moment everyone else does. The specialist could widen his spread until selling cost more than it returned. In a real panic he could step back from his post altogether, and more than once, on the days he was needed most, he did. A market maker's promise is only ever as good as his nerve and his balance sheet, and both are thinnest in a crash. A market that depends on someone's willingness to buy is a market that can be switched off by that someone's fear – and fear is contagious precisely when liquidity is scarce.

The personal tokens of the last decade rediscovered this the hard way, without even a specialist to lose. A creator issued a coin; the only exit was to sell into whoever happened to be bidding; and when confidence wavered, the bidders were the first thing to vanish. The instrument handed its holders a sell button with nothing reliably attached to the other side of it. What those holders lacked was never another token. It was a counterparty who would still be at his post in the bad hour.

The answer, when it finally arrived, was to stop asking a person to be the counterparty and to make the counterparty a rule. Bancor's smart tokens, in 2017, priced a token against a reserve the contract held itself, so the token could always be converted back into that reserve at a price a formula fixed in advance – a market maker with no trader behind it to lose heart. A year later Thibauld Favre described the continuous organization: an enterprise whose token lived permanently on such a curve, raising funds continuously and guaranteeing an exit, instead of selling one fixed batch and leaving its holders to conjure a market afterward. The party across from you was no longer a firm that could lose its nerve. It was arithmetic.

A caper is built on that arithmetic. When a caper opens, its market opens with it – not as a promise to list somewhere later, but as a working counterparty present from the first second. The price is set by how much of the supply has sold, rather than by pairing a buyer to a seller, so there is always a price to buy at and a price to sell at, and neither waits on anyone else showing up. Money paid in fills a reserve; the tokens come out of the curve's own inventory; selling hands them back and draws the reserve down again. There is no order book to thin out, no specialist to widen the spread, no operator holding a key that could close the window or empty the pool. The counterparty is the contract, and the contract has no nerve to lose.

Two things fall out of building the counterparty this way, and both are the reason to bother. The reserve is not a headline figure – it is real collateral, held by the curve, and any holder can reclaim their share of it by selling back or by walking out the exit. And because the price starts at nothing when nothing has sold and can only rise as the supply distributes, there is no cheap floor for an insider to accumulate on before the public arrives; the earliest backer takes the most risk and is paid for it, the latest takes the least. The order in which people show up is priced by one rule that treats all of them alike.

This is what "always tradeable" has to mean if it is to mean anything at all. Markets have promised liquidity since the Amsterdam bourse; what none of them could promise was that the liquidity would be there in the single moment you actually needed it, because it rested on somebody else's willingness to trade with you. The curve takes the willingness out of the equation. It is a market maker that cannot widen its spread out of fear, cannot go insolvent, cannot be talked into closing the window, and cannot be drained by the person who runs it – because no person runs it.

For four hundred years, a standing counterparty was a privilege you had to qualify for. You got one by listing on an exchange that would assign you a specialist, which meant being large enough, and vetted enough, to be worth the assignment. A caper gives the same thing to anyone who can sign a single transaction: a market that comes into being together with the thing it prices, keeps a real reserve behind every unit, and cannot be turned off. The old question was whether someone would take the other side when you wanted out. It stops being a question. Someone always will, because the other side is no longer a someone.