In this lesson you will learn to:
- Define a ledger in plain words.
- Give three historical examples of record keeping.
- Explain what problem a shared ledger solves.
A ledger is a list of changes
A ledger is a record of who owns what and of every change to it. The word comes from the large account books that once lay permanently on a merchant's desk. The idea is far older than the word.
Clay tablets
Some of the earliest known writing, from Mesopotamia more than five thousand years ago, is accounting: clay tablets recording quantities of grain, livestock and labour owed to temples and palaces. Writing seems to have developed, at least partly, because people needed a reliable memory of obligations that was better than anyone's recollection.
Notice what made those tablets trustworthy. They were hard to alter once dried, and they were kept by an institution that people relied on. Durability and a trusted keeper — the same two ingredients you met in lesson 1.1.
Double-entry bookkeeping
In 1494 the Italian mathematician Luca Pacioli published a description of a method already used by Venetian merchants: double-entry bookkeeping. Every transaction is recorded twice, once as a debit and once as a credit, so the books must always balance. If they do not, there is an error somewhere. This was an early form of built-in error detection, and it is still the basis of accounting today.
The stones of Yap
On the Pacific island of Yap, large carved limestone discs called rai were used in important exchanges. Some were too heavy to move. When ownership changed, the stone stayed where it was; what changed was the community's shared memory of who owned it. Economists often cite Yap as an example of a ledger that lives in agreement among many people rather than in a single book.
From books to databases
Today most ledgers are databases run by banks, companies and governments. They are fast and cheap, and they rely on the institution that runs them. Copies may exist for backup, but there is one authoritative version and one organisation decides what goes into it.
What a blockchain changes
A blockchain is still a ledger: a list of changes in order. What changes is who keeps it. Instead of one keeper, many independent participants hold full copies and follow shared rules to decide which changes are valid and in what order they happened. In that sense it is closer to Yap's shared memory than to a bank's database — but with cryptography doing the work of the community's memory.
Key takeaways
- A ledger records who owns what and every change to it.
- Record keeping is thousands of years old and has always relied on durable records and trusted keepers.
- Double-entry bookkeeping introduced built-in error detection.
- A blockchain is a ledger kept by many participants instead of one.
Check yourself
What two qualities made clay-tablet records trustworthy?
They were hard to alter once dried, and they were kept by a trusted institution.
Why must double-entry books always balance?
Each transaction is recorded as both a debit and a credit, so any imbalance reveals an error.
What is different about who keeps a blockchain ledger?
Many independent participants keep full copies and follow shared rules, rather than one organisation keeping the authoritative version.
Sources
- Luca Pacioli (1494), Summa de arithmetica, geometria, proportioni et proportionalita — section on bookkeeping
- Milton Friedman (1991), "The Island of Stone Money", Hoover Institution Working Papers in Economics
This lesson is for general education about how the technology works. It is not a recommendation to acquire, sell or hold any crypto-asset and is not financial advice.