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LibraryConsensus1985Design paperCorpus record

Impossibility of Distributed Consensus with One Faulty Process

FLP. Michael J. Fischer, Nancy A. Lynch and Michael S. Paterson.

No deterministic protocol does all three. Any protocol that is always safe has an execution that never decides.

A reading of the public document. Not a copy of it, and not a claim about a later network that reused the name.

If a designer promises deterministic termination with no timing and one crash, they have claimed to overturn this paper.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
6

Code

Source, repository, and what is actually hosted

  • Journal of the ACMhttps://groups.csail.mit.edu/tds/papers/Lynch/jacm85.pdf
  • The source URL is not a GitHub repository. No code remote is invented.
  • Full text is not mirrored. Public availability is not a licence to copy the file onto this site.
  • Add to a reading list

01 Claim ledger

What the paper is allowed to say

Each row is a sentence already in the study. The status is the same on every row: a model claim, not a live measurement.

  1. Claim 01 · Paper model

    The defect

    People wanted a finite protocol that always terminates, tolerates one crash, and never forks, in a network with no clocks.

  2. Claim 02 · Paper model

    The rule

    No deterministic protocol does all three. Any protocol that is always safe has an execution that never decides.

  3. Claim 03 · Paper model

    How it is put together

    The result is about deterministic asynchronous consensus. Randomness, clocks, or failure detectors are how later systems step around it. It is not a claim that blockchains cannot exist.

  4. Claim 04 · Paper model

    Where the claim stops

    Quoting FLP against a partially synchronous protocol is a category error.

02 Three cuts

Observation, model, falsifier

A desk does not stop at the summary. Each claim is cut three ways, using only this study's own assumptions and checks. Nothing here is a new figure.

  1. 01 The defect

    Observation

    What the study says

    People wanted a finite protocol that always terminates, tolerates one crash, and never forks, in a network with no clocks.

    Model

    What has to hold

    Quoting FLP against a partially synchronous protocol is a category error.

    Falsifier

    What would retire it

    Is the protocol deterministic?

  2. 02 The rule

    Observation

    What the study says

    No deterministic protocol does all three. Any protocol that is always safe has an execution that never decides.

    Model

    What has to hold

    Quoting FLP against a partially synchronous protocol is a category error.

    Falsifier

    What would retire it

    What does it do in the execution the proof says never decides?

  3. 03 How it is put together

    Observation

    What the study says

    The result is about deterministic asynchronous consensus. Randomness, clocks, or failure detectors are how later systems step around it. It is not a claim that blockchains cannot exist.

    Model

    What has to hold

    It does not say liveness is unimportant.

    Falsifier

    What would retire it

    Is the protocol deterministic?

  4. 04 Where the claim stops

    Observation

    What the study says

    Quoting FLP against a partially synchronous protocol is a category error.

    Model

    What has to hold

    Quoting FLP against a partially synchronous protocol is a category error.

    Falsifier

    What would retire it

    Is the protocol deterministic?

03 Sequence

One action, as an operating tape

  1. 01The proof builds a bivalent state, one that could still decide either way.
  2. 02A single message can be delayed to keep the state bivalent.
  3. 03A crash of one process is enough to force that delay.
  4. 04Is the protocol deterministic?

04 Load-bearing

The argument, and where a pitch drops it

  1. Why it is still on the desk

    The cut

    If a designer promises deterministic termination with no timing and one crash, they have claimed to overturn this paper.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    The paper does not rank coins.

  2. After the text

    The cut

    Paxos, Raft and PBFT all give up guaranteed termination in the fully asynchronous case. Nakamoto gives up deterministic finality.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    A later client, parameter or reward formula is a different object from this paragraph.

05 Register

What has to be true

  • Network · Not re-measured

    Quoting FLP against a partially synchronous protocol is a category error.

  • Model · Not re-measured

    The paper does not rank coins.

  • Model · Not re-measured

    It does not say liveness is unimportant.

06 Divergence

What happened after the paper

Paxos, Raft and PBFT all give up guaranteed termination in the fully asynchronous case. Nakamoto gives up deterministic finality.

A later client, parameter set, or reward formula is a different object. Cite this paper for the mechanism. Cite a primary release for the network. This desk has not re-run the proof.

07 Pre-mortem

What to check before you use the idea

  4. 0 of 3 marked on this browser. A mark is a reading note, not a pass, a rating, or a recommendation.

08 Anatomy

The paper, in the order a builder needs

The problem it names

People wanted a finite protocol that always terminates, tolerates one crash, and never forks, in a network with no clocks.

What the design proposes

  • The result is about deterministic asynchronous consensus.
  • Randomness, clocks, or failure detectors are how later systems step around it.
  • It is not a claim that blockchains cannot exist.

How the mechanism is specified

  • The proof builds a bivalent state, one that could still decide either way.
  • A single message can be delayed to keep the state bivalent.
  • A crash of one process is enough to force that delay.

What this page does not treat as proven

  • Quoting FLP against a partially synchronous protocol is a category error.
  • The paper does not rank coins.
  • It does not say liveness is unimportant.

Why the desk still reads it

If a designer promises deterministic termination with no timing and one crash, they have claimed to overturn this paper.

09 Lexicon

Terms, opened into the record

Bivalent
A state from which both decisions are still possible.
Asynchronous
Messages may be delayed arbitrarily.

10 Repository

Every linked record on this page

Underlined words open a page that already exists: a concept, a protocol profile, a failure record, or another paper. If a word is not underlined, this desk does not have a record for it.

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.