Tutorial #8. Frege On Sense and Reference. The Basics

Compositionality Thesis
The meaning of a whole sentence is determined by the meaning of its parts.
Substitutivity Principle
Replacing parts of a sentence with other expressions that mean the same thing should leave the of the whole sentence unchanged.

Frege’s Identity Puzzle
Informative identity statements like
(1) The Morning Star = The Evening Star.
Are different in “cognitive value” from trivial ones like
(2) The Morning Star = The Morning Star.

(2) appears to be true in virtue of language alone -everything is identical with itself-but (1) says something about the world.

"The Morning Star" and "The Evening Star" both mean (refer to) the same heavenly body.

So, by substitutivity, (1) and (2) should mean the same thing.
But they don’t so either we reject substitutivity or we show that “The Morning Star” and “The Evening Star” don’t mean the same thing.


Frege’s Propositional Attitude Puzzle

Propositional attitudes: ways in which people are related to propositions, e.g. believing, hoping, desiring, etc.

(3) Matteo believes that that Mark Twain wrote Huckleberry Finn.
(4) Matteo believes that Samuel Clemens wrote Huckleberry Finn.

(3) may be true even if (4) is false, even though.

(3) and (4) seem to ascribe the same belief to Matteo and hence to say the same thing, so how can one be true but the other false???

!Substitutivity seems to be violated

Toward a solution: the sense/reference distinction

“meaning” is ambiguous

Sense: dictionary meaning, the “thought” (NOT the idea that an individual has) behind an expression or sentence.

Reference: “aboutness,” what an expression picks out.

The sense of a name is an individual concept.
The sense of a predicate is a property or relation.
The sense of a sentence is a proposition.

The reference of a name is an individual.
The reference of a predicate is a set (of individuals or n-tuples of individuals).
The reference of a sentence is a truth value: either The True or The False.

The meaning of a whole sentence is determined by the meaning of its parts, but “meaning” is ambiguous.

Substitutivity Principles

- replacing parts of a sentence with other expressions that have the same sense leaves the sense of the whole sentence unchanged.

- replacing parts of a sentence with other expressions that have the same reference leaves the reference of the whole sentence unchanged.