 Note that the contradiction \(T\langle \lambda \rangle \leftrightarrow \neg T\langle \lambda \rangle\) above expresses: The liar sentence is true if and only if it is not. Compare this to the informal liar presented in the beginning of the article. Tarski’s theorem shows that, in the setting of first-order arithmetic, it is not possible to give what Tarski considers to be an “adequate theory of truth”. The central question then becomes: How may the formal setting or the requirements for an adequate theory of truth be modified to regain consistency—that is, to prevent the liar paradox from trivialising the system? There are many different answers to this question, as there are many different ways to regain consistency. In Section 3 we will review the most influential approaches.