The core puzzle of meaning is that words seem to stand for things in the world (reference), yet the meaning of a word is not simply its referent—the word 'morning star' and 'evening star' refer to the same object but have different meanings. We must distinguish between what a word refers to and what the word means.
Philosophy of language begins with an observation that seems obvious but turns out to be puzzling: words stand for things. "Paris" stands for a city, "red" applies to red things, "runs" is true of things that run. This relationship between language and world is called reference. But if you examine it carefully, reference alone cannot be all there is to meaning — and the morning star/evening star example makes this vivid.
"Morning star" and "evening star" both refer to the planet Venus. If meaning just *were* reference, these two phrases would mean exactly the same thing, and the statement "the morning star is the evening star" would be as trivially true as "Venus is Venus." But that's not how it seems. Ancient astronomers who discovered that the bright object visible in the pre-dawn sky and the bright object visible after sunset were the same planet were learning something — it was a real discovery, not a verbal tautology. Two expressions, one referent, different meanings. Frege's conclusion: meaning and reference are distinct.
The distinction Frege drew — between *sense* (how an expression presents its referent, its mode of presentation) and *reference* (the object picked out) — will become central when you study his Sinn und Bedeutung. For now, the key intuition is that the sense of "morning star" is something like *the celestial body visible in the morning sky*, while the sense of "evening star" is *the celestial body visible in the evening sky*. They present the same object under different descriptions. Knowing both senses and knowing that they refer to the same thing is knowing something extra.
This distinction has cascading consequences. If meaning were just reference, substituting one co-referring term for another should never change truth value. But consider: "Lois believes Superman can fly" can be true while "Lois believes Clark Kent can fly" is false, even though Superman and Clark Kent are the same person. Substituting co-referring names inside belief reports can change whether the report is true. This *substitution failure* is one of the most powerful arguments that meaning involves more than reference — some further descriptive or cognitive content that tracks how the referent is presented to the believer.
Reference works differently for different kinds of expressions, and distinguishing them is part of the foundational toolkit for philosophy of language. Singular terms (proper names, definite descriptions like "the tallest building") pick out individual objects. General terms ("human," "red") apply to or are true of many things. Predicates express properties. These all "refer" in different senses of that word, and getting clear on the distinctions is the groundwork for everything that follows — Frege's full theory, Russell's puzzles about "the present King of France," and eventually Kripke's challenge to the whole descriptivist tradition.
Topics in reflective domains aren't scored by quiz answers. Read, reflect, and mark when you've thought it through.