Immutability

Immutability refers to the challenge of altering records once they’ve been inputted on a blockchain and is a key pillar of censorship resistance. Because, once created, immutable objects retain their state and cannot be changed.

Therefore, both the sender and recipient of a transaction can be confident it will take place at the agreed upon amount. Importantly, from the receivers perspective. They can be confident it will not take place if the sender cannot demonstrate they have the agreed upon funds on hand to send.

Immutability also makes a blockchain’s history auditable. Since every record is stored and users can be confident these records haven’t changed. Any historical transaction can be readily verified.

While a well secured blockchain in practice is immutable and minimally vulnerable to outside interference from malicious actors. No blockchain can be considered completely immutable because of the risk of a successful 51% attack.

In practice it is assumed blockchains are immutable though. Which is why you will often hear them described as immutable ledgers.

Further Reading Immutability

Blockchain Immutability – Why Does it Matter?