Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Intension And Extension
A fundamental step in the discussion of meaning was Gottlob Frege's distinction between "sense" and "reference", which led to the distinction between "intension" and "extension". The "referent" of a word is the object it refers to, the "sense" of that word is the way the referent is given. For example, "the star of the morning" and "the star of the evening" have two different senses but the same referent (they both refer to the planet Venus). A more important example: propositions of classical Logic can only have one of two referents, true or false.
The "extension" of a concept is all the things that belong to that concept. For example, the extension of "true" is the set of all the propositions that are true. The "intension" of that concept is the concept itself. For example, the extension of "red" is all the objects that are red, whereas the intension of "red" is the fact of being red. There is an intuitive relationship between sense and intension, and between reference and extension.
But the relationship between sense and reference is not intuitive at all, as proved by the difficulty in handling indexicals (words such as “i”) and demonstratives (such as “this”). The proposition “I am Piero Scaruffi” is true or false depending on who utters it. The proposition “I am right and you are wrong” has two completely opposite meanings depending on who utters it.
A number of alternatives to Frege’s analysis have been proposed over the decades: Saul Kripke's and Hilary Putnam's “causal theory of reference” (which assumes a causal link between a word and what it stands for); Kripke's distinction of “rigid designators” and “non-rigid designators” in the context of possible worlds; and Richard Montague's intensional-logic approach (in which the sense of an expression is supposed to determine its reference). These are all different views on how sense and reference relate.
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