what makes a language decidable
Decidability. Definition: A language is called decidable if there exists a method-any method at all-to determine whether a given word belongs to that language or not. Working hypothesis I: Decidability is well defined above.roof: Surely, a decidable language is recognizable. Moreover, if a language is decidable, then so is its complement, and hence that complement is recognizable. Now suppose a language L and its complement are recognizable. Let A be a recognizer for L, and B for its complement.