Blockchain Basics Module
Consensus & Finality
How decentralized networks agree on one history — and when that history becomes safe to rely on
Core path (recommended): Consensus problem → Safety/liveness → Fork choice → PoW/PoS overview → Confirmations/finality → Practical limits
This is the required path to complete the module. All other articles are optional.
Start core pathWhat this module covers
Consensus is the problem of agreement without a central authority under faults and delays.
This module covers correctness goals (safety and liveness), fork choice and chain selection, high-level consensus mechanism families (PoW vs PoS), and the difference between confirmations and finality.
Hard stop: before incentive engineering, MEV, and protocol-specific details.
This module is for
- Anyone who needs a correct mental model of agreement without a central authority
- Developers who want to reason about reorg risk and finality guarantees
- Users who want to understand “when is it final?”
This module is not
- Incentive engineering, MEV, and validator economics
- Protocol-specific details (Bitcoin/Ethereum/Solana specifics)
- Attack playbooks and adversarial “how-to”
Stage 0
Orientation: The Consensus Problem
What problem is consensus actually solving?
Understand the problem statement: agreement without a central authority under faults and delays.
Core
What Is Consensus?
Supporting (intuition)
Optional intuition and mental models.
Why “Just Voting” Doesn’t Work
Why Delays and Faults Are Assumed
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Famous Consensus Failures (Conceptual)
You can move on when:
- You can describe consensus as agreement over shared history/state transitions.
- You can explain why faults and delays are assumed by default.
- You can separate the goal (agreement) from the mechanism (how).
Stage 1
Block Production & Selection
Who gets to propose the next block, and why this does not break decentralization?
Understand block proposal rights and competition as the entry point to consensus thinking.
Core
What Is Mining in Crypto and How It Works?
You can move on when:
- You can explain who proposes blocks in PoW at a high level and why not anyone can do it.
- You can connect block competition to security intuitively.
- You can separate what users observe (forks/reorg risk) from protocol details.
Stage 2–3
Alternative block proposal & security model
What changes when block proposal is stake-based instead of work-based?
Introduce Proof of Stake as an alternative to mining, at a high level.
Core
What Is Proof of Stake?
You can move on when:
- You can explain PoS as stake-weighted block proposal/validation (high-level).
- You can state the core security intuition: attacking history requires controlling stake (not compute).
Stage 2
Safety, Liveness & Assumptions
What does it mean for consensus to “work”?
Lock in correctness criteria before mechanisms.
Core
Safety vs Liveness
Faults and Adversaries
Supporting (intuition)
Optional intuition and mental models.
Honest vs Faulty vs Adversarial Nodes (Intuition)
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Typical Fault Assumptions (Conceptual)
You can move on when:
- You can define safety and liveness in plain language.
- You can describe the types of faults consensus assumes.
- You can explain why adversarial behavior changes the design.
Stage 3
Fork Choice & Chain Selection
When multiple valid blocks exist, how do nodes choose?
Understand that consensus ≠ fork choice, but fork choice is crucial for convergence.
Core
Fork Choice Rule
Longest Chain vs Heaviest Chain
Supporting (intuition)
Optional intuition and mental models.
Why Reorgs Happen
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
How Explorers Show Reorgs (Conceptual)
You can move on when:
- You can define a fork choice rule.
- You can explain why “longest” is usually a proxy for accumulated weight.
- You can explain why short reorgs happen before convergence.
Stage 4
Consensus Mechanisms (High-Level)
How do different systems produce blocks but aim for the same outcome?
Understand mechanism families without protocol-specific detail.
Boundary
This stage is high-level mechanism only — not incentive engineering, MEV, or protocol-specific details.
Core
Proof of Work
Supporting (intuition)
Optional intuition and mental models.
BFT-Style Finality (Preview)
What Is Staking in Crypto?
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Energy vs Capital Trade-offs (Conceptual)
You can move on when:
- You can describe PoW and PoS at a system level.
- You can describe what “weight” means in each family (work vs stake).
- You understand this is mechanism, not incentive engineering.
Stage 5
Confirmations & Finality
When does history become safe to rely on?
Separate probabilistic confidence from stronger guarantees.
Core
Confirmations & Finality
Probabilistic Finality
Supporting (intuition)
Optional intuition and mental models.
Economic Finality
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Confirmation Depth in Practice (Conceptual)
You can move on when:
- You can explain confirmations as increasing confidence.
- You can explain finality as stronger guarantees under assumptions.
- You can explain why some systems have probabilistic finality.
Stage 6
Practical Guarantees & Limits
What can applications safely assume — and what can still break?
Remove the illusion of absolute finality.
Core
What “Irreversible” Means in Practice
Supporting (intuition)
Optional intuition and mental models.
Common Finality Failure Modes
Choosing Confirmation Thresholds
Reference (how to observe the system)
Optional verification via explorers, clients, wallets, and documentation.
Real-World Rollback Scenarios (Conceptual)
You can move on when:
- You can explain why “irreversible” is conditional on assumptions.
- You can name common failure modes that break finality assumptions.
- You can explain why applications choose thresholds.
Stage 7
Boundaries & Next Modules
What consensus enables — and what it does not solve?
Close the module before incentives/MEV and bridge into the next topics.
Hard stop (covered later)
- Incentive engineering and fee markets
- MEV and ordering games
- Protocol-specific details
Leads naturally to
- Fees & Incentives
- Scaling & Layer 2
- Security & MEV (advanced domain)
Supporting (intuition)
Optional intuition and mental models.
Network Propagation and Latency
Block Construction and Ordering
Incentives and Rewards
Completion checklist
If you can answer these, you have the module’s mental model.
- What problem does consensus solve in a decentralized network?
- What do safety and liveness mean, and what assumptions does consensus make?
- What is a fork choice rule and why do reorgs happen?
- How do PoW and PoS differ at a high level?
- What is the difference between confirmations and finality?
- What does “irreversible” mean in practice and what can still break?
FAQ
Key concepts
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Fees & Incentives
Why fees, rewards, and incentives shape blockchain behavior.