Sense and Reference

In philosophy and linguistics, the sense of a linguistic expression, sometimes understood in contrast to its referent. For example, the expressions “the morning star” and “the evening star” have different meanings, though their referent (Venus) is the same. Some expressions have meanings but no referents (“the present king of France”) or referents but no meanings (“that”). The literal or conventional meaning of an expression may differ from what a speaker of that expression means by uttering it on a particular occasion; this is the case with similes, statements uttered ironically, and statements that convey various “conversational implicatures,” as in the following examples: “She entered the house and shot him” implicates that she shot him in the house after she entered it, though this is not part of the sentence's literal meaning; “John has three sons” implicates that John has no more than three sons, though again the sentence does not literally say this. Other non-literal aspects of meaning include the potential for carrying out various “speech acts” (see speech act theory); e.g., uttered in the appropriate circumstances, the sentence “I christen thee the Joseph Stalin,” constitutes the act of naming a ship, and the sentence “I am cold” constitutes a request to close the window.
[Encyclopedia Brittanica]

Frege's distinction [between Sense and reference] rejects a view put forward by John Stuart Mill, according to which a proper name has no meaning above and beyond the object to which it refers (its referent or reference). That is, the word "Aristotle" just means Aristotle, that person, and no more. It does not mean "The writer of De Caelo." Hence, the sentence Aristotle was Greek says only that that person was Greek. It does not say that the writer of De Caelo was Greek. That is, it permits that Aristotle might not have written De Caelo. More generally, for any given proposition about Aristotle, one can use the name without believing that proposition to be true of Aristotle.

Frege's central objection to the view that a name's meaning is no more than its referent is that, if a and b are names of the same object, then the identity statement a = b must mean the same as a = a. Yet clearly the first can convey information in a way that the second cannot; that Samuel Clemens is Samuel Clemens is just trivial, but Samuel Clemens is Mark Twain is interesting. Why? Or, why is Cicero is Tully more significant than Cicero is Cicero? And, by the same token, Samuel Clemens wrote novels and Mark Twain wrote novels would have to mean the same thing but, again, the two sentences seem to convey different information.

A related problem concerns attributions of belief. It might well seem that, since Deep Throat and Mark Felt mean the same thing, the two sentences Everyone knows that Deep Throat is Deep Throat and Everyone knows that Deep Throat is Mark Felt must also mean the same thing. (Whether that is so is a matter of some controversy, however.) But that is intuitively wrong.

Frege's distinction is meant to make sense of these phenomena. He postulates that, in addition to a reference (Bedeutung), a proper name possesses what he calls a sense (Sinn), some aspect of the way its reference is thought of that can differ, even between two names that refer to the same object. The important difference between Mark Twain and Samuel Clemens, for example, is a "difference in the mode of presentation of that which is designated". The sense of an expression is "that wherein the mode of presentation is contained". Thus, one can know both the names Mark Twain and Samuel Clemens without realizing that they are about the same object, because they present that object in different ways, that is, they have different senses.

Summarizing:

* The reference is the object that the expression refers to. For instance, the name Mark Twain refers to Mark Twain, i.e. Samuel Clemens, the man who lived in the U.S. and wrote satires. The name Samuel Clemens also refers to that man. Hence the two have the same reference.
* The sense is the "cognitive significance" or "mode of presentation" of the referent.
* Names with the same reference may have different senses.

Frege uses the following example to illustrate this view. Let a, b, and c be three lines each of which joins one vertex of a triangle to the median of the opposite side. Then it is a theorem that

[t]he point of intersection of a and b is then the same as the point of intersection of b and c. So we have different designations for the same point, and these names ('point of intersection of a and b', 'point of intersection of b and c') likewise indicate the mode of presentation; and hence the statement contains actual knowledge. Gottlob Frege, Über Sinn und Bedeutung

At one time, it was common to identify the sense of a name with an identifying description, which would put Frege's view close to Russell's description theory of names. For example, the name "Mark Twain" might just mean: The man who wrote Tom Sawyer, and Samuel Clemens might mean: The eldest son of John and Jane Clemens. Thus the reference would be determined as whatever fit the description. This interpretation is now almost unanimously rejected by scholars. Unfortunately, however, a detailed replacement has not been forthcoming. But what is clear is that Frege certainly did not mean that the sense of a name is merely a collection of ideas a particular user of a name happens to associate with it: Because they figure into the meanings of terms in a public language and can be communicated, senses must be objective.
[From Wikipedia]