Start with the problem it solves. An ordinary database has an owner, and the owner's copy is correct by definition. A public blockchain has no owner and no referee, yet every participant must end up with the same ledger. Consensus is the procedure that gets them there: it makes proposing valid blocks profitable, makes proposing invalid ones worthless, and gives every <a href="/glossary/node/">node</a> a deterministic rule for picking between competing versions of history.
Two families dominate. <a href="/glossary/proof-of-work/">Proof of work</a> ties the right to produce a block to real-world expenditure, mostly electricity and specialised hardware, so rewriting the past means redoing that expenditure. <a href="/glossary/proof-of-stake/">Proof of stake</a> ties it to coins locked up as collateral, so a misbehaving <a href="/glossary/validator/">validator</a> can have part of its own stake destroyed. Both approaches share one idea: attacking the chain should cost more than it could ever pay.
The common misunderstanding is thinking consensus produces truth. It produces agreement on ordering, nothing more. The network can confirm that a transaction was signed correctly and included at a particular point; it cannot confirm that a price feed was accurate, that a smart contract does what its marketing says, or that the person who signed meant to. Garbage that follows the rules is still recorded faithfully.
There are also real trade-offs worth naming. Faster confirmation and cheaper fees usually come from having fewer, better-resourced participants, which quietly trims <a href="/glossary/decentralization/">decentralisation</a>. Different mechanisms also treat finality differently: some settle a block permanently after a defined process, others only make reversal progressively more expensive over time.
Key takeaways
- Consensus decides the order of transactions and who may add the next block; it never judges whether the underlying information is true or wise.
- Every mechanism works by making dishonesty more expensive than honesty, which means security is economic rather than absolute.
- Cheaper and faster consensus designs usually reduce the number of independent participants, so speed and decentralisation pull against each other.
Consensus Mechanism — frequently asked questions
Is consensus the same thing as mining?
No. Mining is one specific way of reaching consensus, used by proof-of-work networks, where computers compete to solve a hashing puzzle. Consensus is the broader concept: the rules for agreeing on a shared ledger. Proof-of-stake chains reach consensus with staked collateral and validators instead, and other designs use committees, reputation or permissioned voting.
What happens if nodes disagree about the correct chain?
Temporary disagreement is normal, because blocks take time to travel the network. The consensus rules include a tie-breaker, such as following the chain with the most accumulated work or the most attested weight, so nodes converge again within a block or two. If the disagreement is about the rules themselves rather than the data, you get a fork instead.
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