 Functions whose values are truth values are called propositional functions. Frege also referred to them as concepts (Begriffe). A typical kind of such functions (besides the ones denoted by predicates) are the functions denoted by propositional connectives. Negation, for example, can be interpreted as a unary function converting the True into the False and vice versa, and conjunction is a binary function that returns the True as a value when both its argument positions are filled in by the True, etc. Propositional functions mapping \(n\)-tuples of truth values into truth values are also called truth-value functions.