There was a time when people thought that the Morning Star and the Evening Star were different objects. Then it was discovered that they are, in fact, the same object, namely, Venus, observed at different times. Frege used this discovery in his analysis of identity. The Morning Star = The Evening Star, a = b.
What he was rightly worried about was how to express the content of the discovery. What does "a = b" convey that is not just "a = a"? If words mean whatever they refer to, and "Morning Star" and "Evening Star" refer to the same thing (Venus), then the sentence "The Morning Star is the Evening Star" and "The Morning Star is the Morning Star" finally mean the same thing. And this can't be right, because the first of those sentence summarizes an important scientific discovery while the second is simply a tautology.
Frege solved the problem by distinguishing between the "sense" (Sinn) and the "reference" (Bedeutung) of a proposition. I won't get into that here. My own solution rejects the identification of the Morning Star with the Evening Star. When we refer to the Morning Star we are referring to a point of light in the Morning sky, visible before the sun comes up, when we refer to the Evening Star we are referring to a point of light visible in the Evening. When we refer to Venus we are referring to a planet. (Leave aside the completely different meaning of Venus as a goddess.)
I sometimes think this makes me a "postmodernist". I am willing to multiply the practical problems of reference in order to avoid creating theoretical problems of meaning. I am willing to play with the signifier in order to avoid some hard work with the concept. Obviously, both solutions, Frege's and mine, have their advantages and disadvantages. Frege was concerned with the identity of Venus—actually, he was worried about identity as such. I am worried about "the difference between Venus"—difference as such.
At least on some days.
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This is my last post on postmodernism (a pun I forgot to exploit!) for a while. Next week, I'm going to begin an obsessive love affair with the paragraph. It's probably going to occupy this blog up until Easter. I want show that academic writing amounts to constructing and arranging prose paragraphs. In time and space.