Definition
Tarski's undefinability theorem, stated and proved by Alfred Tarski in 1933, is an important limitative result in mathematical logic, the foundations of mathematics, and in formal semantics. Informally, the theorem states that "arithmetical truth cannot be defined in arithmetic".
Related concepts
Abstract logicAckermann set theoryAleph numberAlfred TarskiAlgebraic logicAlphabet (formal languages)ArgumentArithmetical hierarchyArityAtomic formulaAtomic model (mathematical logic)Atomic sentenceAtopy (philosophy)Austrian Academy of SciencesAutomata theoryAutomated theorem provingAxiomAxiom of choiceAxiom schemaAxiomatic systemAxiomatization of Boolean algebrasBanach–Tarski paradoxBijectionBinary operationBoolean algebraBoolean algebras canonically definedBoolean functionCantor's diagonal argumentCantor's paradoxCantor's theoremCardinalityCartesian productCategorical theoryCategory (mathematics)Category of setsCategory theoryChaitin's incompleteness theoremChurch encodingChurch–Turing thesisClass (set theory)Classical logicCodomainCognitive closure (philosophy)Coherence theory of truthCompactness theoremComplement (set theory)Complete theoryCompleteness (logic)Computability theoryComputable functionComputable setComputably enumerable setConcrete categoryConsensus theory of truthConservative extensionConsistencyConstructible universeConstruction of the real numbersConstructive set theoryConstructivist epistemologyContinuum hypothesisCorrespondence theory of truthCountable setDecidability (logic)Decision problemDeductive systemDeflationary theory of truthDiagonal lemmaDiagram (mathematical logic)Domain of a functionEffective methodElement (mathematics)Elementary diagramElementary equivalenceElementary function arithmeticEmpty setEntscheidungsproblemEnumerationEpistemic theories of truthEquiconsistencyEquivalence relationEuclid's ElementsEuclidean geometryExistential quantificationExpression (mathematics)Extension by definitionsExtension by new constant and function namesExtensionalityFactorialFibonacci numberFinitary relationFinite-valued logicFinite model theoryFinite setFirst-order arithmeticFirst-order logicFixed-point logicForcing (mathematics)Formal grammarFormal languageFormal proofFormal semantics (logic)Formal systemFormation ruleFoundations of geometryFoundations of mathematicsFree logicFree variables and bound variablesFunction (mathematics)Function symbolFunctional predicateFuzzy setGeneral set theoryGeorge BoolosGrothendieck universeGround expressionGround formulaGödel's completeness theoremGödel's incompleteness theoremGödel's incompleteness theoremsGödel numberGödel numberingHalting problemHereditary setHigher-order logicHilbert's axiomsHilbert systemHistory of logicHistory of mathematical logicIgnoramus et ignorabimusImage (mathematics)Inaccessible cardinalIndependence (mathematical logic)IneffabilityInferenceInfinite-valued logicInfinite setInformation theoryInhabited setInjective functionInterpretation (logic)Interpretation (model theory)Interpretation functionIntersection (set theory)IsomorphismJoel David HamkinsJohn Lucas (philosopher)John P. 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