Marx starts with a simple assumption: gold is the money-commodity. Gold does not make goods comparable. Every commodity already holds human labour, so one special commodity can measure them all, and gold is the one that does it. Set 1 ton of iron against 2 ounces of gold and the iron has a price. That price is only an idea. The owner of iron, linen or corn has to lend his goods his tongue, or hang a ticket on them, before anyone hears it. Because the act is ideal, a trader can price millions of pounds' worth of goods without touching a single coin. Yet the price still depends on a real metal. If gold and silver both act as measures, every commodity has two prices, and they sit quietly side by side only while silver stays at 15 to 1 against gold. When the ratio moves, the double standard breaks. Marx then splits the job in two. As measure of value, money turns labour into prices. As standard of price, it is a fixed weight of metal. That is why money-names come loose from weights. The pound began as a real pound of silver. Foreign coins arrived in early Rome, the dearer metal pushed out the cheaper, and kings and princes debased their coins for centuries until only the names were left. A name tells you as little about money as the name Jacob tells you about a man. Price can also stray from value. A quarter of wheat priced at £2 is still priced if the figure rises to £3 or falls to £1, and things that are no commodities at all, such as conscience and honour, can be given a price. Uncultivated land has a price and no value, since no labour is in it. Above all, a price is only a promise. The owner of iron who points to his price as proof that it is already money gets the answer St Peter gave Dante: the weight and the alloy of the coin are fine, but have you got it in your purse? Under the ideal measure of values, Marx says, lurks the hard cash.
So he follows a seller to market. The weaver of linen takes 20 yards, priced at £2, sells them, and spends the £2 on a family Bible. Commodity, money, commodity. For the weaver it is only a swap of his product for someone else's. But the first step, the sale, is a leap Marx calls the salto mortale of the commodity. If the leap fails, the linen is unharmed and its owner is not. The linen must meet a real want, and rival weavers may already have filled it. Behind the weaver's back the old way of weaving may change, so that the labour that was socially necessary yesterday is not so today, and the owner of the money is only too eager to prove it from the prices of his competitors. Even if every piece holds only the necessary labour, the community may have put too much of its total labour into weaving, and then all the linen counts as one article: caught together, hung together. Commodities are in love with money, Marx says, but the course of true love never did run smooth. Meanwhile the deal has two sides. The weaver's sale is also a purchase by the man who holds the two gold pieces, and those pieces are themselves the changed form of a quarter of wheat. The seller of the Bible turns the £2 into brandy. So there are always four extremes and three players, and the farmer's sale of wheat lets the weaver sell linen, which lets the Bible seller sell his book, which lets the distiller sell his eau-de-vie. This is why circulation is not barter. B's commodity replaces A's, but A and B never swap anything with each other, and the money does not vanish when the goods change hands: circulation sweats money from every pore. Marx calls it childish to say that because every sale is a purchase, sales and purchases must balance. Nobody is bound to buy just because he has sold. Let the gap between the two acts grow too wide and their hidden unity asserts itself as a crisis. That is only the possibility of crisis, Marx adds, and turning it into fact needs relations that simple circulation does not yet contain.
Next he watches the money instead of the goods. The weaver's coins do not come back to him. They pass from his pocket to the Bible seller's, so money moves steadily away from its starting point, and that makes it look as if money moves the goods when it is the goods changing form. Each coin is displaced twice, once when the linen is sold and once when the Bible is bought. How much money does all this need? Take a quarter of wheat, 20 yards of linen, a Bible and 4 gallons of brandy at £2 each. Sold at the same moment in four places, they need £8. Sold in a chain, the same £2 makes four moves and comes to rest in the distiller's pocket. So the money required is the sum of the prices divided by the number of moves a coin makes. A coin that moves faster means fewer coins, which is why a banker can draw sovereigns out of circulation by throwing in one-pound notes. When circulation slows, the public sees money appear less often and blames a shortage of it, when really sales and purchases have come apart. Some economists of the 17th and 18th centuries watched new gold and silver arrive and decided that prices had risen because there was more of it. Marx says they had it backwards: the sum of prices sets the quantity of money, and the value of the metal moves the prices. Coin then wears out. No sooner has it left the mint than it is on the high road to the melting pot, and its name and its real weight begin to part. That makes room for a token to take its place. Silver and copper tokens do the small purchases, where coins pass fastest, and paper notes printed by the State do the same. The paper has no value of its own and works only while it does not exceed the gold that would circulate. If the State issues double, £1 becomes the name of one eighth of an ounce of gold instead of one quarter, and prices double.
