Frege proposed that the meaning of a sentence is its truth value in "Über Sinn und Bedeutung" (close to "On Sense and Meaning"). This is not correct because some (many) English sentences do not have any truth value.
For example, an interrogative sentence cannot have a truth value because it seems to be both true and false at the same time. A declarative sentence which contains an if (whether) clause cannot be assigned a truth value too because it can be true and false as well. Lastly, sentences contain logic contradictions such as the Liar paradox or Richard's paradox do not have truth values.
Is this view of Frege accepted only for propositions that are only part of sentences?