How did Gottlob Frege distinguish the sense of an expression from its referent?

Gottlob Frege distinguished between the referent (Bedeutung) and the sense (Sinn) of an expression to explain how language functions beyond simple naming.12

• Referent (Bedeutung): This is the actual object or entity in the world to which an expression refers.13
• Sense (Sinn): This is the "mode of presentation" of the referent—the specific way in which the expression picks out or identifies that object.13

Frege argued that while different expressions can share the same referent, they may possess different senses, which explains why certain identity statements are informative rather than trivial. For example, "Everest" and "Chomolungma" refer to the same mountain, but they present it through different senses, making the statement "Everest is Chomolungma" a meaningful discovery rather than a tautology like "Everest is Everest".1

Furthermore, this distinction accounts for why substituting coreferring terms can change the truth value of belief sentences. Because the sense determines how an individual is "picked out," a person might believe one expression is true while doubting another, even if both refer to the same person.3