To understand why, we need to go back to the 14th century.
That was when Italian merchants and bankers began using the double-entry bookkeeping method. This method, made possible by the adoption of Arabic numerals, gave merchants a more reliable record-keeping tool, and it let bankers assume a powerful new role as middlemen in the international payments system. Yet it wasn’t just the tool itself that made way for modern finance. It was how it was inserted into the culture of the day.
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In 1494 Luca Pacioli, a Franciscan friar and mathematician, codified their practices by publishing a manual on math and accounting that presented double-entry bookkeeping not only as a way to track accounts but as a moral obligation. The way Pacioli described it, for everything of value that merchants or bankers took in, they had to give something back. Hence the use of offsetting entries to record separate, balancing values—a debit matched with a credit, an asset with a liability.
Pacioli’s morally upright accounting bestowed a form of religious benediction on these previously disparaged professions. Over the next several centuries, clean books came to be regarded as a sign of honesty and piety, clearing bankers to become payment intermediaries and speeding up the circulation of money. That funded the Renaissance and paved the way for the capitalist explosion that would change the world.
Yet the system was not impervious to fraud. Bankers and other financial actors often breached their moral duty to keep honest books, and they still do—just ask Bernie Madoff’s clients or Enron’s shareholders. Moreover, even when they are honest, their honesty comes at a price. We’ve allowed centralized trust managers such as banks, stock exchanges, and other financial middlemen to become indispensable, and this has turned them from intermediaries into gatekeepers. They charge fees and restrict access, creating friction, curtailing innovation, and strengthening their market dominance.
The real promise of blockchain technology, then, is not that it could make you a billionaire overnight or give you a way to shield your financial activities from nosy governments. It’s that it could drastically reduce the cost of trust by means of a radical, decentralized approach to accounting—and, by extension, create a new way to structure economic organizations.
A new form of bookkeeping might seem like a dull accomplishment. Yet for thousands of years, going back to Hammurabi’s Babylon, ledgers have been the bedrock of civilization. That’s because the exchanges of value on which society is founded require us to trust each other’s claims about what we own, what we’re owed, and what we owe. To achieve that trust, we need a common system for keeping track of our transactions, a system that gives definition and order to society itself. How else would we know that Jeff Bezos is the world’s richest human being, that the GDP of Argentina is $620 billion, that 71 percent of the world’s population lives on less than $10 a day, or that Apple’s shares are trading at a particular multiple of the company’s earnings per share?
A blockchain (though the term is bandied about loosely, and often misapplied to things that are not really blockchains) is an electronic ledger—a list of transactions. Those transactions can in principle represent almost anything. They could be actual exchanges of money, as they are on the blockchains that underlie cryptocurrencies like Bitcoin. They could mark exchanges of other assets, such as digital stock certificates. They could represent instructions, such as orders to buy or sell a stock. They could include so-called smart contracts, which are computerized instructions to do something (e.g., buy a stock) if something else is true (the price of the stock has dropped below $10).
What makes a blockchain a special kind of ledger is that instead of being managed by a single centralized institution, such as a bank or government agency, it is stored in multiple copies on multiple independent computers within a decentralized network. No single entity controls the ledger. Any of the computers on the network can make a change to the ledger, but only by following rules dictated by a “consensus protocol,” a mathematical algorithm that requires a majority of the other computers on the network to agree with the change.
Once a consensus generated by that algorithm has been achieved, all the computers on the network update their copies of the ledger simultaneously. If any of them tries to add an entry to the ledger without this consensus, or to change an entry retroactively, the rest of the network automatically rejects the entry as invalid.
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