# The liar paradox

- kind: problem
- status: partial
- year: -350
- authors: attributed to Eubulides

**Statement.** Is the sentence 'This sentence is false' true or false?

Tarski showed in 1933 that a sufficiently strong language cannot define its own truth predicate, which blocks the paradox by moving truth to a metalanguage. Kripke's 1975 theory of truth allows gaps instead. Gödel used a relative of the paradox to prove incompleteness. Formal fixes exist; whether any captures ordinary truth is debated.

Posed c. 4th century BCE, attributed to Eubulides.

## Related problems

- The original curation links this problem to [Hilbert's second problem: consistency of arithmetic](/wiki/Problem:hilbert-second.md); the argument for the link has not been written yet.

## Sources

- [Wikipedia: Liar paradox](https://en.wikipedia.org/wiki/Liar_paradox)

[Value and reason](/wiki/Space:value.md) · [Philosophy](/wiki/Continent:philosophy.md)

## Relations

- related to [hilbert-second](/wiki/Problem:hilbert-second.md) — The original curation links this problem to Hilbert's second problem: consistency of arithmetic; the argument for the link has not been written yet.

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