PHIL 309: Twentieth Century Analytic Philosophy
LARKIN: Fall 2003
SIUE
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I. Frege’s Puzzle
P1: Identity claims of the form ‘a = a’ can differ in cognitive significance from identity claims of the form ‘a = b’, even though they are both true, because while ‘a = a’ is trivial ‘a = b’ might be informative and only discoverable a posteriori.
1a: “Hesperus is Hesperus” is totally uninformative and trivial.
1b: “Hesperus is Phosphorous” in fact required empirical investigation to discover.
P2: If identity claims are about the referents of the terms involved, then ‘a = a’ and ‘a = b’ would have the same cognitive value, both claiming that some object (i.e., the referent of ‘a’) is identical to itself.
2a: If “Hesperus is Hesperus” is about the referent of the term, then it says that Venus is identical to Venus.
2b: If “Hesperus is Phosphorous” is about the referents of terms, then it also says that Venus is identical to Venus.
P3: If identity claims are about the names ‘a’ and ‘b’ having different referents, then ‘a = b’ is not really about the world and could not be such that it is only discoverable a posteriori.
3a: If “Hesperus is Phosphorous” is about the names involved, then it says that the name ‘Hesperus’ has the same referent as the name ‘Phosphorous’.
3b: But then the claim is purely linguistic—saying only that we use two names to refer to the same object, which is a claim about the conventions of our language and not about objects in the world.
C1: So identity claims are neither about the referents of the terms being identical nor about the names involved being co-referential.
C2: So there must be some layer of meaning between the terms and the referents—terms must have a sense as well as a referent.
A. For senses to solve the puzzle, they must be such that:
1. A single referent can be presented by different senses.
2. A sense must not be a purely linguistic/conventional entity but rather something ‘out there’ in the world, such that it is possible that it requires empirical investigation to discover that two different senses have the same referent.
B. Some other things Frege says about senses:
1. They determine a unique referent—if two terms have different referents, then they have different senses.
2. The sense of a term is grasped by every competent user of that term.
3. The sense of a term cannot be identified with some subjective psychological entity like an idea or a description that might be associated with a term in a particular individual’s mind. Senses occupy a ‘third realm’—they are neither objective physical things nor subjective psychological things.
4. The sense of a compound expression is determined by the senses of its constituent parts.
5. The sense of a sentence is a proposition, which then determines as a referent a truth-value (either the True or the False).