Public / private blockchain

Public and permissionless

Bitcoin and Ethereum are open to anyone. You need no account and no approval to read the ledger, send a transaction or run a validating node.

This is what makes them censorship resistant: there is no gatekeeper to petition, and no administrator who can reverse a transaction or freeze an address.

The costs are real. Throughput is limited, fees rise with demand, and every transaction is public forever.

Private and permissioned

A permissioned ledger restricts participation to approved parties. A group of banks, hospitals or logistics firms runs the nodes and decides who joins.

The gains are throughput, confidentiality, and a governance structure that regulated industries can actually sign off on. The loss is the property that made blockchains novel: if a known group controls the validators, that group can rewrite the record.

Consortium chains

The middle ground: several organisations share control, no single one dominates. Common in trade finance, supply chains and interbank settlement.

This is often a sensible fit for the problem, and worth judging on its own terms rather than against a decentralisation ideal it never aimed for.

The question worth asking

For any private chain: what does the blockchain add that a shared database with good access controls would not?

Sometimes the answer is solid, usually where participants genuinely do not trust each other and want a tamper-evident shared history. Often the honest answer is that a database would do, and the blockchain is there for the prospectus.

Asking the question directly is the fastest way to tell the two apart.