Editing Tarski's undefinability theorem (section)

{{short description|Theorem that arithmetical truth cannot be defined in arithmetic}}
{{more footnotes|date=August 2023}}
'''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".<ref>Cezary Cieśliński, "How Tarski Defined the Undefinable," ''European Review'' 23.1 (2015): 139–149.</ref>

The theorem applies more generally to any sufficiently strong [[formal system]], showing that truth in the standard model of the system cannot be defined within the system.