 According to Frege, the semantic value of a sentence is just its truth-value, and the semantic value of a proper name is its referent (that is, the object to which it refers). Once we have fixed the semantic values assigned to sentences and proper names, it is easy to determine what kinds of semantic value to assign to expressions of other syntactic categories. For instance, the semantic value of a monadic predicate will have to be a function from objects to truth-values. Frege calls such functions concepts.