How does Frege explain the difference of cognitive value between informative and trivial identity sentences?

Abstract

This paper aims to make a brief reconstruction of the Frege’s attempts for to solve the problem of to explain the difference of cognitive value that there is between sentences of the forms “a = a” and “a = b”, which don’t seem to differ in content, because they seem to speech on the same object, saying that it is identical himself. In Begriffsschrift, Frege considers the identity sentences as belonging to the metalanguage and his singular terms as referring to himself. Thus, the sentences of the quoted forms would differ in cognitive value because, in the former case, is wrapped only one singular term, while, in the latter case, are wrapped two singular terms. In Über Sinn und Bedeutung, Frege rejects that solution, by revising his first system and making his famous distinction between the Sinn ─ sense ─ and the Bedeutung of expressions. With such revision, Frege starts to understand that the difference in cognitive value is because of the fact that the two sorts of sentence express different senses, although having same Bedeutung.