Sense

The way an expression presents what it refers to - what is left over when two names for the same thing still differ.

Theme: Logic, language and interpretation
Tradition: Analytic
Term: Sinn
Term fixed: 1892

In plain terms

Two expressions can pick out the same thing and still not be interchangeable. Something distinguishes them, and it is not what they refer to, because that is identical.

Frege called that something the sense: the way the thing is presented. The morning star and the evening star present one planet in two ways, and which way matters - to what you can learn from a sentence, to whether you believe it, and to whether substituting one for the other preserves the truth of what you said.

The test is simple. If two names really were interchangeable, swapping them in any sentence would change nothing. Swap them inside a sentence about what someone believes and the result can go from true to false, which shows something besides the referent is at work.

As a philosopher would put it

Frege's argument is that if a name contributed only its referent, then a = b and a = a would say the same thing, and one is informative while the other is not. Sense is what distinguishes them: the mode of presentation, grasped by anyone competent with the expression, public rather than psychological.

Sense determines reference and is not determined by it, which gives the theory its shape. It also explains failure of substitutivity in belief contexts - the standard case of what Frege calls indirect reference, where an expression refers to its own customary sense.

Russell rejected the distinction, analysing descriptions away instead; the field followed him for sixty years and then followed Kripke, whose modal arguments cut against descriptive senses for names. What survives is contested. Two-dimensional semantics reconstructs something sense-like while accepting Kripke's points; direct-reference theorists deny that names have sense at all and owe an account of Frege's puzzle; and Fregeans reply that the puzzle is still there and still unanswered.

Where you meet it

The rules of zoological nomenclature exist because the same animal is regularly described twice.

A specimen is collected, described and named. Elsewhere, sometimes decades later, another specimen of the same species is described and named again by someone unaware of the first. Two names, one taxon. The International Code of Zoological Nomenclature settles it by priority: the earliest available name is valid and the later becomes a junior synonym.

What the Code cannot do is make the names equivalent. The junior name carries its own type specimen, its own original description, its own literature and its own body of records, and a paper from 1953 using it means something a modern paper using the senior name does not - which is why synonymy lists are printed rather than the old names being erased. The referent is one animal. The two names present it through different histories, and taxonomists handle that distinction daily without a theory of it.

What is actually disputed

Whether names have sense.

Direct-reference theorists hold that a name contributes only its bearer, and account for Frege's puzzle pragmatically - the difference between the two identity statements is a difference in what is conveyed rather than in what is said. Critics reply that this leaves belief reports unexplained, since substituting co-referring names can plainly turn a true report into a false one.

Neo-Fregeans keep sense while accepting Kripke's argument that senses are not descriptions, which requires saying what a non-descriptive mode of presentation is - and no account of that has commanded agreement.

Underneath is a question about how public senses can be. Frege insisted they are objective and shareable, unlike private ideas. If two competent speakers associate different modes of presentation with the same name, either sense is not fully public or they are not both fully competent, and neither answer is comfortable.

Commonly confused with

Meaning 1892 Sense is a technical component of meaning, not a synonym. On Frege's account meaning divides into sense and reference, and later theories divide it differently.
the senses Sight, hearing and the rest are unrelated, and the collision is an accident of English. German keeps Sinn and Sinne apart no better.

Defined against

Reference The pair is Frege's distinction and the founding move of the modern subject

Philosophers

Bertrand Russell Rejects the distinction and analyses descriptions away instead
Ludwig Wittgenstein The name-object model that leaves no room for sense
Rudolf Carnap Intension and extension, the successor apparatus
Willard Van Orman Quine Suspicion of meanings as entities at all
John Stuart Mill Connotation and denotation, the nineteenth-century predecessor

Works

The Foundations of Arithmetic Frege's setting, where the distinction is developed
Principia Mathematica The rival treatment
Tractatus Logico-Philosophicus Where names have bearers and nothing else
Naming and Necessity The arguments that undo descriptive sense
The Logical Syntax of Language The intension-extension reconstruction

Schools

Logical Atomism Where the distinction is refused
Cambridge Analysis Where the formal apparatus develops
Vienna Circle Where intension replaces sense
Ordinary Language Philosophy Where the whole framing is questioned
Pittsburgh School (Sellarsian Realism) Where inferential role does the work sense did

Related concepts

Reference 1905 · Meaning 1892 · Proposition 1903 · Concept 1781 · Definition c. 330 BC

Frege introduces Sinn in 1892 precisely to explain how an identity statement can be informative; the term is his and the problem is the one that made modern philosophy of language a subject.