Nineteenth Century Philosophy
Philosophy of Mathematics and Logic
What was Gottlob Frege’s landmark insight about meaning?
Frege’s theory of language was set forth in three essays: “Function and Concept,” “On Concept and Object,” and “Sense and Reference.” He noted that some identity statements are true and informative. For example, the sentence “Venus is Venus,” does not tell me anything, but the sentence, “The Morning Star is the Evening Star,” is informative, although it means the same as “Venus is Venus,” because Venus is in fact both the Morning Star and the Evening Star.
How can this be? Frege’s explanation was that there is a difference between “sense” and “reference.” Reference is the actual planet Venus, in this case. But sense is how the planet is referred to by the term “Morning Star” (i.e., a bright object in the eastern sky before sunrise). Thus, “The Morning Star” does not stand for Venus itself, but for the sense of how Venus is presented. This is why the two sentences that appear to be equivalent really are different. It explains why it is not informative to say that Venus is Venus or that The Morning Star is the Morning Star, but it is informative to say that Venus is the Morning Star.