The T-schema ("truth schema", not to be confused with "Convention T") is used to check if an inductive definition of truth is valid, which lies at the heart of any realisation of Alfred Tarski's semantic theory of truth. Some authors refer to it as the "Equivalence Schema", a synonym introduced by Michael Dummett.[1]
The T-schema is often expressed in natural language, but it can be formalized in many-sorted predicate logic or modal logic; such a formalisation is called a "T-theory."[citation needed] T-theories form the basis of much fundamental work in philosophical logic, where they are applied in several important controversies in analytic philosophy.
As expressed in semi-natural language (where 'S' is the name of the sentence abbreviated to S): 'S' is true if and only if S.
Example: 'snow is white' is true if and only if snow is white.