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### Single Idea 15342

#### [catalogued under 3. Truth / A. Truth Problems / 2. Defining Truth]

Full Idea

Tarski's Theorem on the undefinability of truth says in a language sufficiently rich to talk about itself (which Gödel proved possible, via coding) the liar paradox can be carried out.

Gist of Idea

Tarski proved that any reasonably expressive language suffers from the liar paradox

Source

report of Alfred Tarski (The Concept of Truth for Formalized Languages [1933]) by Leon Horsten - The Tarskian Turn 02.2

Book Reference

Horsten,Leon: 'The Tarskian Turn' [MIT 2011], p.18

A Reaction

The point is that truth is formally indefinable if it leads inescapably to contradiction, which the liar paradox does. This theorem is the motivation for all modern attempts to give a rigorous account of truth.

Related Idea

Idea 6006
If you say truly that you are lying, you are lying **[Eubulides, by Dancy,R]**