Frege argued that linguistic expressions have both a sense (Sinn) and a reference (Bedeutung). The sense is the mode of presentation—the conceptual content that determines which object is referred to—while the reference is the object itself. Two expressions can have the same reference but different senses, explaining how 'morning star' and 'evening star' differ in meaning despite referring to the same planet.
Work through the morning star / evening star example and other identity puzzles to see why simple reference theories fail. Then study how Frege's distinction solves them.
Sense is just what the speaker means—sense is the objective, language-determined mode of presentation, not individual psychology. Reference requires a complete description—Frege allowed incomplete descriptions to have sense.
From your study of meaning and reference basics, you understand that words and phrases point to things in the world — a name like "Mount Everest" picks out the mountain, and a predicate like "is tall" picks out a property. A simple reference theory of meaning says that the meaning of a name just is its referent — the object it picks out. This theory is attractive in its economy, but Frege identified a problem that forces a more complex picture: identity statements can be informative, and a pure reference theory cannot explain why.
Consider: "Hesperus is Hesperus" versus "Hesperus is Phosphorus." Both statements are true, and both names — Hesperus (the evening star) and Phosphorus (the morning star) — turn out to refer to the same object: the planet Venus. On a pure reference theory, both sentences express the same thing — the identity of Venus with itself — and therefore should have the same cognitive value. But they do not. "Hesperus is Hesperus" is trivially true, knowable by logic alone. "Hesperus is Phosphorus" was a genuine astronomical discovery. Learning it tells you something about the world. How can two sentences with the same reference have different cognitive significance?
Frege's solution is to distinguish sense (Sinn) from reference (Bedeutung). The reference of a term is the object it picks out. The sense is the mode of presentation — the conceptual route by which the reference is determined. "Hesperus" and "Phosphorus" have the same reference (Venus) but different senses: one presents Venus as the bright object visible in the evening sky, the other as the bright object visible in the morning sky. The identity statement "Hesperus is Phosphorus" is informative precisely because it tells you that two different modes of presentation lead to the same object. This is a fact about the world that could not be known from the senses alone.
Frege extended the distinction beyond names to whole sentences. The reference of a sentence is its truth value (True or False). The sense of a sentence is the thought or proposition it expresses — the condition the world must satisfy for the sentence to be true. Two sentences can express the same thought with different wording, or two sentences can share a truth value without expressing the same thought. This architecture — sense determines reference, reference is what sense presents — becomes the backbone of formal semantic theory.
An important clarification: sense is not the same as what a particular speaker happens to have in mind when they use a word. Frege insisted that sense is objective and public — it belongs to the language, not to individual psychology. This is why the theory is not simply about speakers' intentions but about the semantic structure of language itself. The distinction between sense and reference sets up the central questions that Russell, Kripke, and later philosophers of language will contest: Are senses descriptive? Can names have sense without description? Could reference be fixed by causal chains rather than by sense? You will engage these questions directly as you build toward Kripke's causal theory of naming.
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